Co-reporter:Maxwell Reinhardt;Simon Dalgleish;Yoshiaki Shuku;Louisa Reissig;Michio M. Matsushita;Jason Crain;Kunio Awaga
Physical Chemistry Chemical Physics 2017 vol. 19(Issue 9) pp:6768-6776
Publication Date(Web):2017/03/01
DOI:10.1039/C6CP08685C
The structure and electronic properties of a novel cobalt half sandwich complex of cyclopentadiene (Cp) and diaminonaphthalene (DAnap) [CpCo(DAnap)] are described and compared to the previously reported diaminobenzene derivative [CpCo(DAbnz)] in view of their potential for (opto)electronic device application. Both complexes show stable redox processes, tunable through the diaminoacene ligand, and show strong absorption in the visible region, with additional transitions stretching into the near infrared (NIR). CpCo(DAnap) crystallises with a particularly large unit cell (9301 Å3), comprising 32 molecules, with a gradual rotation over 8 molecules along the long c-axis. In the solid state the balance of the optical transitions in both complexes is reversed, with a suppression of the visible band and an enhancement of the NIR band, attributed to extensive intermolecular electronic interaction. In the case of CpCo(DAnap), highly crystalline thin films could be formed under physical vapor deposition, which show a photocurrent response stretching into the NIR, and p-type semiconductor behavior in field effect transistors with mobility values of the order 1 × 10−4 cm2 V−1 s−1. The device performance is understood through investigation of the morphology of the grown films.
Co-reporter:Michal R. Maciejczyk;J. A. Gareth Williams;Marek Pietraszkiewicz
RSC Advances (2011-Present) 2017 vol. 7(Issue 78) pp:49532-49535
Publication Date(Web):2017/10/20
DOI:10.1039/C7RA07671A
A truxene molecule incorporating a sulfur atom at one of the three bridgehead positions has been prepared through an efficient route, together with its oxidized analogue (featuring an SO2 unit) and brominated derivatives. The photophysical, electrochemical and thermal properties of the compounds are presented: the materials show high thermal stability and the ability to form amorphous glasses. This central monothiatruxene core offers multiple routes to further modifications, thereby opening a way to the synthesis of a variety of novel functional materials beyond the parent truxene.
Co-reporter:Tianyue Li;Yue Hu;Carole A. Morrison;Wenjun Wu;Hongwei Han
Sustainable Energy & Fuels (2017-Present) 2017 vol. 1(Issue 2) pp:308-316
Publication Date(Web):2017/03/29
DOI:10.1039/C6SE00061D
Two organic–inorganic iodobismuthates, C5H6NBiI4 ([py][BiI4]) and C6H8NBiI4 ([mepy][BiI4]), have been prepared with their structures revealed by single-crystal X-ray diffraction. One-dimensional BiI4− anionic chains built by edge-sharing BiI6 octahedra were found in both materials; short I⋯I, I⋯C contacts and hydrogen bonding give rise to three-dimensional intermolecular interactions. Both compounds are semiconductors, with band gaps of around 2.0 eV, and the contribution from the organic moieties to the conduction band minimum has been derived by density functional theory. Solid-state optical and electrochemical studies performed on powders and thin films were carried out, and their stabilities under an ambient environment have been demonstrated. Their use as the absorber layer in printable mesoscopic solar cells without any hole transport material has led to efficiencies up to 0.9%, showing a promising new approach towards the development of lead-free third-generation photovoltaic materials.
Co-reporter:Michal Maciejczyk, Aruna Ivaturi and Neil Robertson
Journal of Materials Chemistry A 2016 vol. 4(Issue 13) pp:4855-4863
Publication Date(Web):02 Mar 2016
DOI:10.1039/C6TA00110F
Four spiro[fluorene-9,9′-xanthene] (SFX) derivatives, SFX-TAD, SFX-TCz, SFX-TPTZ and SFX-MeOTAD have been synthesized for use as hole-transport materials and fully characterized by 1H/13C NMR spectroscopy, mass spectrometry, XRD and DSC. Their thermal, optical and electrochemical properties were investigated. The use of different substituents affects the highest occupied molecular orbital (HOMO) energy level proving the versatility of the central core towards the facile and low-cost preparation of spiro-hole-transport materials. Among the synthesized SFX derivatives, SFX-MeOTAD was employed as hole-transporting material (HTM) and the performance tested in perovskite solar cells with device architecture glass/FTO/compact TiO2/mesoporous Al2O3/CH3NH3PbI3−xClx/HTM/Au. SFX-MeOTAD gave a comparable efficiency to spiro-MeOTAD, demonstrating great potential for use of the SFX family as cost effective and versatile hole conductors facilitating commercialization of perovskite solar cells (PSCs).
Co-reporter:Yue Hu, Aruna Ivaturi, Miquel Planells, Chiara L. Boldrini, Alessio Orbelli Biroli and Neil Robertson
Journal of Materials Chemistry A 2016 vol. 4(Issue 7) pp:2509-2516
Publication Date(Web):16 Dec 2015
DOI:10.1039/C5TA09133K
The common trend in designing dyes for use in DSSCs with iodide-based electrolyte is based on a donor–π spacer–acceptor (D–π–A) architecture. Here, we report two ‘donor-free’ cyanoacrylic end-functionalized oligo(3-hexylthiophene) dyes (5T and 6T). Despite having no donor group, both dyes show reversible first oxidation process. Both 5T and 6T have n-hexyl alkyl chains to retard aggregation at different positions as well as different numbers of thiophene moieties. However, the dyes showed similar absorption properties and redox potentials. The DSSCs based on these dyes give power conversion efficiencies of more than 7%, although a significant difference in the VOC and FF has been observed. Using electrochemical impedance spectroscopy, this is attributed to the presence of more trap states when 6T attaches to TiO2 and modifies the surface, mainly affecting the fill factor. Overall, these dyes introduce a new and effective design concept for liquid-electrolyte DSSC sensitisers.
Co-reporter:Emily Allwright, Georg Silber, Jason Crain, Michio M. Matsushita, Kunio Awaga and Neil Robertson
Dalton Transactions 2016 vol. 45(Issue 22) pp:9363-9368
Publication Date(Web):12 May 2016
DOI:10.1039/C6DT01166G
Electrochemical deposition has been used to prepare a thin film of neutral 4′,4-(3-alkyl)-thiophene-5′,5-hydogen-nickel and copper dithiolenes (Ni–C2, Cu–C2). The application of molecular electrodeposition provides a means to solution process molecular semiconductors of poor solubility, which results from the strong intermolecular interaction required for charge transport. Both Ni–C2 and Cu–C2 form continuous thin films that show intense NIR absorptions, extending to 1800 nm and 2000 nm respectively giving evidence for the strong intermolecular interactions in the solid state. Both films are highly conducting and temperature dependence of resistance gave an activation energy of 0.42 eV and 0.072 eV respectively, with the near-metallic behaviour of Cu–C2 attributed to the additional presence of an unpaired electron.
Co-reporter:Yue Hu
Frontiers of Optoelectronics 2016 Volume 9( Issue 1) pp:38-43
Publication Date(Web):2016 March
DOI:10.1007/s12200-016-0568-5
Since their invention, dye-sensitized solar cells (DSSCs) have received enormous research attention from scientists with different background due to the possibility of low-cost production and fabrication on flexible substrates. One of the most important components in DSSCs is the sensitizing dye, including metal-complexes and metal-free organic dyes. The donor-π bridge-acceptor (D-π-A) structure is the mainstream in the design of organic sensitizers because it facilitates efficient charge-transfer toward the TiO2 upon excitation. However, some sensitizers that do not follow this structure, or have some modification upon this structure, also present good efficiency when applied in DSSC devices. This review summarizes these atypical dyes in order to inspire more diverse designs toward highly efficient DSSCs.
Co-reporter:Yue Hu
The Journal of Physical Chemistry C 2016 Volume 120(Issue 28) pp:15027-15034
Publication Date(Web):June 27, 2016
DOI:10.1021/acs.jpcc.6b03610
Co-reporter:Che-Wei Hsu, Yongbiao Zhao, Hsiu-Hsuan Yeh, Chin-Wei Lu, Cong Fan, Yue Hu, Neil Robertson, Gene-Hsiang Lee, Xiao Wei Sun and Yun Chi
Journal of Materials Chemistry A 2015 vol. 3(Issue 41) pp:10837-10847
Publication Date(Web):16 Sep 2015
DOI:10.1039/C5TC02261D
Potential dianionic chelates, 5,5′-bis(trifluoromethyl)-2H,2′H-3,3′-bipyrazole (bipzH2) and 5,5′-(1-methylethylidene)-bis(3-trifluoromethyl-1H-pyrazole) (mepzH2), were synthesized from Claisen condensation employing ethyl trifluoroacetate with 2,3-butanedione and with 3,3-dimethyl-2,4-pentanedione, followed by hydrazine cyclization. These chelates were then utilized in the preparation of four emissive Pt(II) metal complexes [Pt(tbbpy)(bipz)] (1), [Pt(msbpy)(bipz)] (2), [Pt(tbbpy)(mepz)] (3) and [Pt(msbpy)(mepz)] (4), where tbbpy and msbpy represent 4,4′-di-t-butyl-2,2′-bipyridine and 4,4′-dimesityl-2,2′-bipyridine, respectively. Single crystal X-ray structural analyses of 2 and 3 were executed to unveil the basic coordination geometry around the Pt(II) center as well as the π–π stacking interaction in the solid state. These complexes are essentially non-emissive in solution (Q. Y. = 0.2–0.4%), but are highly luminescent in the solid state with QY of 52% and 83% and τobs of 368 ns and 8.37 μs for 1 and 3, respectively. Their photophysical properties were measured and discussed on the basis of computational approaches. For applications, non-doped organic light emitting diodes (OLEDs) were fabricated using 1 and 3 as emitters, exhibiting red-orange emission with a maximum luminance of 43000 cd m−2, an EQE of 19.0%, a CE of 21.0 cd A−1 and a PE of 15.5 lm W−1, and yellow emission with a maximum luminance of 5100 cd m−2, an EQE of 7.1%, a CE of 21.0 cd A−1 and a PE of 11.3 lm W−1, respectively. The particularly higher OLED efficiencies of 1versus3 highlight the design principle of Pt(II) based phosphors, particularly for the fabrication of a non-doped OLED architecture.
Co-reporter:Xing Li, Yue Hu, Irene Sanchez-Molina, Ying Zhou, Fengtao Yu, Saif A. Haque, Wenjun Wu, Jianli Hua, He Tian and Neil Robertson
Journal of Materials Chemistry A 2015 vol. 3(Issue 43) pp:21733-21743
Publication Date(Web):21 Sep 2015
DOI:10.1039/C5TA07254A
Three new quinoxaline-based organic dyes (AQ201, AQ202, and AQ203), containing thiophene, 3,4-ethylenedioxythiophene (EDOT), and cyclopentadithiophene (CPDT) in the π-system, respectively, have been designed and synthesized for dye-sensitized solar cells. Different from the traditional donor–π-bridge–acceptor (D–π–A) type dyes, the dissymmetric π-bridge on both sides of quinoxaline enables great flexibility in fine-tuning the absorption spectra and energy levels of the resultant molecules. By changing the π-bridge between the bulky triphenylamine donor and quinoxaline group, a negative shift was observed regarding the highest occupied molecular orbital (HOMO) levels of AQ201, AQ202, and AQ203 dyes (0.88, 0.79, and 0.72 V vs. NHE, respectively), while the lowest unoccupied molecular orbital (LUMO) levels of these dyes remained the same (−1.19, −1.20, and −1.20 V vs. NHE, respectively), which, in turn, resulted in a gradual shift of the absorption spectra of AQ dyes. The absorption spectra properties of the dyes are also analysed by density functional theory. The calculated results in combination with the experiments indicate that the absorption bands are mainly dominated by charge transfer transitions from the HOMO and HOMO−1 orbital to the LUMO. In all cases, the [Co(bpy)3]2+/3+ redox-shuttle afforded superior solar cell performance compared to I−/I3−. More importantly, dye AQ202 shows the highest power conversion efficiency (PCE) of 8.37% with the [Co(bpy)3]2+/3+ based electrolyte by maintaining a balance between the spectral absorption range and driving force for dye regeneration. Transient photocurrent decay experiments as well as electrochemical impedance spectroscopy indicate that the lower HOMO levels lead to higher electron lifetime and dye regeneration efficiency.
Co-reporter:John Mallows, Miquel Planells, Vishal Thakare, Reshma Bhosale, Satishchandra Ogale, and Neil Robertson
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 50) pp:27597
Publication Date(Web):December 10, 2015
DOI:10.1021/acsami.5b09291
A novel hybrid visible-light photodetector was created using a planar p-type inorganic NiO layer in a junction with an organic electron acceptor layer. The effect of different oxygen pressures on formation of the NiO layer by pulsed laser deposition shows that higher pressure increases the charge carrier density of the film and lowers the dark current in the device. The addition of a monolayer of small molecules containing conjugated π systems and carboxyl groups at the device interface was also investigated and with correct alignment of the energy levels improves the device performance with respect to the quantum efficiency, responsivity, and photogeneration. The thickness of the organic layer was also optimized for the device, giving a responsivity of 1.54 × 10–2 A W–1 in 460 nm light.Keywords: nickel oxide; organic; oxygen vacancies; photodetector; pulsed laser deposition; surface modifier
Co-reporter:Kuan-Yu Liao, Che-Wei Hsu, Yun Chi, Ming-Kuan Hsu, Szu-Wei Wu, Chih-Hao Chang, Shih-Hung Liu, Gene-Hsiang Lee, Pi-Tai Chou, Yue Hu, and Neil Robertson
Inorganic Chemistry 2015 Volume 54(Issue 8) pp:4029-4038
Publication Date(Web):April 7, 2015
DOI:10.1021/acs.inorgchem.5b00281
Tetradentate bis(pyridyl azolate) chelates are assembled by connecting two bidentate 3-trifluoromethyl-5-(2-pyridyl)azoles at the six position of pyridyl fragment with the tailored spiro-arranged fluorene and/or acridine functionalities. These new chelates were then utilized in synthesizing a series of Pt(II) metal complexes [Pt(Ln)], n = 1–5, from respective chelates L1–L5 and [PtCl2(DMSO)2] in 1,2-dimethoxyethane. The single-crystal X-ray structural analyses were executed on 1, 3, and 5 to reveal the generalized structures and packing arrangement in crystal lattices. Their photophysical properties were measured in both solution and solid state and are discussed in the context of computational analysis. These L1–L5 coordinated Pt(II) species exhibit intense emission, among which complex 5 shows remarkable solvatochromic phosphorescence due to the dominant intraligand charge transfer transition induced by the new bis(pyridyl azolate) chelates. Moreover, because of the higher-lying highest occupied molecular orbital of acridine, complex 5 can be considered as a novel bipolar phosphor. Successful fabrication of blue and white organic light-emitting diodes (OLEDs) using Pt(II) complexes 3 and 5 as the phosphorescent dopants are reported. In particular, blue OLEDs with 5 demonstrated peak efficiencies of 15.3% (36.3 cd/A, 38.0 lm/W), and CIE values of (0.190, 0.342) in a double-emitting layer structure. Furthermore, a red-emitting Os(II) complex and 5 were used to fabricate warm-white OLEDs to achieve peak external quantum efficiency, luminance efficiency, and power efficiency values as high as 12.7%, 22.5 cd/A, and 22.1 lm/W, respectively.
Co-reporter:Antonio Abate, Miquel Planells, Derek J. Hollman, Vishal Barthi, Suresh Chand, Henry J. Snaith and Neil Robertson
Physical Chemistry Chemical Physics 2015 vol. 17(Issue 4) pp:2335-2338
Publication Date(Web):04 Dec 2014
DOI:10.1039/C4CP04685D
Two diacetylide-triphenylamine hole-transport materials (HTM) with varying redox potential have been applied in planar junction TiO2–[CH3NH3]PbI3−xClx solar cells leading to high power-conversion efficiencies up to 8.8%. More positive oxidation potential of the HTM gives higher VOC and lower JSC illustrating the role of matching energy levels, however both HTMs gave efficient cells despite a difference of 0.44 V in their redox potentials.
Co-reporter:Ioanna Iliopoulou, Delphine Thaeron, Ashley Baker, Anita Jones, and Neil Robertson
Journal of Agricultural and Food Chemistry 2015 Volume 63(Issue 31) pp:7066-7073
Publication Date(Web):July 10, 2015
DOI:10.1021/acs.jafc.5b02543
The black carrot dye is a mixture of cyanidin molecules, the nuclear magnetic resonance (NMR) spectrum of which shows a highly overlapped aromatic region. In this study, the 1H NMR (800 MHz) aromatic chemical shifts of the mixture were fully assigned by overlaying them with the characterized 1H NMR chemical shifts of the separated compounds. The latter were isolated using reverse-phase high-performance liquid chromatography (RP-HPLC), and their chemical shifts were identified using 1H and two-dimensional (2D) correlation spectroscopy (COSY) NMR spectroscopy. The stability of the black carrot mixture to heat exposure was investigated at pH 3.6, 6.8, and 8.0 by heat-treating aqueous solutions at 100 °C and the powdered material at 180 °C. From integration of high-resolution 1H NMR spectra, it was possible to follow the relative degradation of each compound, offering advantages over the commonly used ultraviolet/visible (UV/vis) and HPLC approaches. UV/vis spectroscopy and CIE color measurements were used to determine thermally induced color changes, under normal cooking conditions.
Co-reporter:Yue Hu;Irene Sanchez-Molina;Saif A. Haque
European Journal of Inorganic Chemistry 2015 Volume 2015( Issue 36) pp:5864-5873
Publication Date(Web):
DOI:10.1002/ejic.201501071
Abstract
A series of new RuII complexes has been synthesised, with different azo ligands as additional chromophore. The dyes are all intensely colored due to MLCT and ILCT transitions in the visible region. The photophysical study of the dyes, carried out by UV/Vis absorption and emission spectroscopy, showed unusual features such as intense solvatochromism and solvent-dependent extinction coefficients. The energies of these excited states have been tuned by changing the electron density across the series of azo ligands, and this results in different contributions from each charge transfer process for the different complexes and consequently, different emission behavior. The detailed behaviour of these dyes was further studied and interpreted through electrochemical, structural and computational techniques. The dyes do not work well as sensitisers for DSSCs and this is investigated by emission spectroscopy on TiO2 and ZrO2 films, suggesting poor charge injection to TiO2.
Co-reporter:Nina Chadwick;D. Kishore Kumar;Aruna Ivaturi;Benjamin A. Grew;Hari M. Upadhyaya;Lesley J. Yellowlees
European Journal of Inorganic Chemistry 2015 Volume 2015( Issue 29) pp:4878-4884
Publication Date(Web):
DOI:10.1002/ejic.201500633
Abstract
We have synthesised Ru(H2-dcbpy)(N,N′-Y2-bpy)(NCS)2 dyes (where N = 4, 5; Y = F, Cl, Br; N is the position on the bipyridyl ring where the halogen substituent is located) for dye-sensitised solar cells. We show that careful consideration of the position of the substituent, in conjunction with the nature of the substituents, on a bpy ring is important to optimize the solar cells performance. Changing the position (from 4,4′ to 5,5′) along with the nature of the halogen (F, Cl, or Br) substituents were observed to cause changes in the electronic and spectroscopic properties of the dyes as well as influence the recombination rates at the TiO2–dyes–I–/I3– interface affecting the performance of the dyes in DSSCs.
Co-reporter:Gylen Odling ;Dr. Neil Robertson
ChemSusChem 2015 Volume 8( Issue 11) pp:1838-1840
Publication Date(Web):
DOI:10.1002/cssc.201500298
Co-reporter:Luca Pilia, Maddalena Pizzotti, Francesca Tessore, Neil Robertson
Inorganica Chimica Acta 2015 430() pp: 114-119
Publication Date(Web):
DOI:10.1016/j.ica.2015.03.002
Co-reporter:Gylen Odling, Nina Chadwick, Ewan Frost-Pennington, D. Kishore Kumar, Aruna Ivaturi, Hari M. Upadhyaya, Neil Robertson
Polyhedron 2015 Volume 89() pp:45-48
Publication Date(Web):29 March 2015
DOI:10.1016/j.poly.2014.12.021
An in situ nucleophilic aromatic substitution reaction has been observed and applied as a simple route to introduce functionality to the 4,4′ positions of bipyridyl units coordinated to a Ru(II) centre. This has been used in the synthesis of a new Ru(II) sensitiser complex [RuII(4,4′-dicarboxy-2,2′-bipyridyl)(4,4′-dithiocyanate-2,2′-bipyridyl)dithiocyanate] 1 for use in dye-sensitised solar cells. 1 exhibits improved light harvesting in the 350–450 nm region in comparison with N719 and produced cells with power conversion efficiencies of 3.18%.In situ nucleophilic aromatic substitution provides a simple route to functionalization at the 4,4′ positions of bipyridyl units co-ordinated to a Ru(II) centre. The resulting new Ru(II) sensitiser [RuII(4,4′-dicarboxy-2,2′-bipyridyl)(4,4′-dithiocyanate-2,2′-bipyridyl)dithiocyanate] is studied in dye-sensitised solar cells.
Co-reporter:Antonio Abate;Miquel Planells;Derek J. Hollman;Samuel D. Stranks;Annamaria Petrozza;Ajay Ram Srimath Kada;Yana Vaynzof;Seep K. Pathak;Henry J. Snaith
Advanced Energy Materials 2014 Volume 4( Issue 13) pp:
Publication Date(Web):
DOI:10.1002/aenm.201400166
Co-reporter:Luca Pilia;Michele Serri;Michio M. Matsushita;Kunio Awaga;Srine Heutz
Advanced Functional Materials 2014 Volume 24( Issue 16) pp:2383-2388
Publication Date(Web):
DOI:10.1002/adfm.201303218
The magnetic, thin-film structural, conductivity, and magnetoresistance properties of [Ni(quinoline-8-thiolate)2] ([Ni(qt)2]) are studied. The conducting and magnetoresistance properties are studied in single crystals and in evaporated thin films through deposition on an interdigitated electrode array. Non-linear conductivity interpreted through a space-charge limited conduction mechanism with charges injected from the electrodes is observed. Under applied magnetic field, the material displays giant negative magnetoresistance above 50% at 2 K in both single crystals and in evaporated thin films. The effect can still be observed at 200 K and is interpreted in terms of a double exchange mechanism with the shape of the curve determined by the magnetic anisotropy. The unique observation of giant magnetoresistance (GMR) as an intrinsic effect in an evaporated thin film of paramagnetic molecules opens up new possibilities in organic spintronics.
Co-reporter:Emily Allwright, Dominik M. Berg, Rabie Djemour, Marc Steichen, Phillip J. Dale and Neil Robertson
Journal of Materials Chemistry A 2014 vol. 2(Issue 35) pp:7232-7238
Publication Date(Web):30 Jul 2014
DOI:10.1039/C4TC01134A
Electrochemical deposition is shown to be a novel technique to deposit films of N,N′-dibutylperylene-3,4:9,10-bis(dicarboximide) (BuPTCDI) dye that avoids the need for high vacuum or solubilising side chains on the molecule. The technique exploits the higher solubility of the reduced ionic form of the dye over the neutral form. BuPTCDI was chemically reduced to solubilise and then electrochemically oxidised to form a film on various substrates. The properties of the films were investigated by UV/Vis spectroscopy, Photoluminescence, Raman spectroscopy, X-ray diffraction, SEM and photoconductivity showing the successful deposition of the BuPTCDI molecules. The technique was also used to deposit films on interdigitated-electrode substrates enabling measurement of field-effect mobility.
Co-reporter:Kuan-Lin Wu, Yue Hu, Chun-Tien Chao, Ya-Wen Yang, Ting-Yun Hsiao, Neil Robertson and Yun Chi
Journal of Materials Chemistry A 2014 vol. 2(Issue 45) pp:19556-19565
Publication Date(Web):07 Oct 2014
DOI:10.1039/C4TA04208E
Three isomeric Ru(II) metal complexes with distinctively oriented tpiq ancillary chelates, TFRS-80a, 80b and 80c, were prepared from the condensation of Ru(4,4′-diethoxycarbonyl-2,2′-bipyridine) (p-cymene)Cl with tpiqH, i.e. 6-(5-(2,6-bis(hexyloxy)phenyl)thiophen-2-yl)-1-(3-(trifluoromethyl)-1H-pyrazol-5-yl)isoquinoline. Photophysical and electrochemical investigations, together with DFT and TD-DFT calculations, allowed a comprehensive understanding of their basic properties in both solution state and on TiO2 surface. DSC cells with both an ultra-thin layer of transparent TiO2 (3.6 μm) and I−/I3− electrolyte were fabricated, for which the symmetric sensitizers TFRS-80a and 80c showed better performances (η = 8.37 and 8.26%) over that of the asymmetric counterpart TFRS-80b (η = 5.55%), the latter suffered from poor dye loading and consequently lowered JSC and VOC. In sharp contrast, all DSC cells with [Co(phen)3]2+/3+ electrolyte gave superior efficiencies (η = 8.36–9.06%), for which the thiocyanate-free architecture, the improved light harvesting capability, and the possession of conjugated and bulky 5-(2,6-bis(hexyloxy)phenyl)thiophen-2-yl functional moieties are three primary factors governing the observed results.
Co-reporter:Miquel Planells, Antonio Abate, Henry J. Snaith, and Neil Robertson
ACS Applied Materials & Interfaces 2014 Volume 6(Issue 19) pp:17226
Publication Date(Web):September 18, 2014
DOI:10.1021/am5050532
A series of conjugated 3-hexylthiophene derivatives with a cyanoacrylic acid group has been prepared with conjugation length from one up to five thiophene units (1T–5T). The UV–vis spectra, photoluminescence spectra, electrochemical data and DFT calculations show lowering of LUMO energies and red-shift of absorption into the visible as the thiophene chain length increases. TiO2/P3HT solar cells were prepared with prior functionalization of the TiO2 surface by 1T–5T and studies include cells using undoped P3HT and using P3HT doped with H-TFSI. Without H-TFSI doping, photocurrent generation occurs from both the oligothiophene and P3HT. Doping the P3HT with H-TFSI quenches photocurrent generation from excitation of P3HT, but enables very effective charge extraction upon excitation of the oligothiophene. In this case, photocurrent generation increases with the light harvesting ability of 1T–5T leading to a highest efficiency of 2.32% using 5T. Overall, we have shown that P3HT can act in either charge generation or in charge collection, but does not effectively perform both functions simultaneously, and this illustrates a central challenge in the further development of TiO2/P3HT solar cells.Keywords: Dye-sensitized solar cells; oligothiophenes; organic semiconductors; P3HT; Solar cells; TiO2
Co-reporter:Charlotte L. Linfoot, Markus J. Leitl, Patricia Richardson, Andreas F. Rausch, Oleg Chepelin, Fraser J. White, Hartmut Yersin, and Neil Robertson
Inorganic Chemistry 2014 Volume 53(Issue 20) pp:10854-10861
Publication Date(Web):July 23, 2014
DOI:10.1021/ic500889s
The complexes [Cu(I)(POP)(dmbpy)][BF4] (1) and [Cu(I)(POP)(tmbpy)][BF4] (2) (dmbpy = 4,4′-dimethyl-2,2′-bipyridyl; tmbpy = 4,4′,6,6′-tetramethyl-2,2′-bipyridyl; POP = bis[2-(diphenylphosphino)-phenyl]ether) have been studied in a wide temperature range by steady-state and time-resolved emission spectroscopy in fluid solution, frozen solution, and as solid powders. Emission quantum yields of up to 74% were observed for 2 in a rigid matrix (powder), substantially higher than for 1 of around 9% under the same conditions. Importantly, it was found that the emission of 2 at ambient temperature represents a thermally activated delayed fluorescence (TADF) which renders the compound to be a good candidate for singlet harvesting in OLEDs. The role of steric constraints within the complexes, in particular their influences on the emission quantum yields, were investigated by hybrid-DFT calculations for the excited triplet state of 1 and 2 while manipulating the torsion angle between the bipyridyl and POP ligands. Both complexes showed similar flexibility within a ±10° range of the torsion angle; however, 2 appeared limited to this range, whereas 1 could be further twisted with little energy demand. It is concluded that a restricted flexibility leads to a reduction of nonradiative deactivation and thus an increase of emission quantum yield.
Co-reporter:Luca Pilia, Maddalena Pizzotti, Francesca Tessore, and Neil Robertson
Inorganic Chemistry 2014 Volume 53(Issue 9) pp:4517-4526
Publication Date(Web):April 24, 2014
DOI:10.1021/ic5002094
We report the synthesis, characterization, nonlinear-optical (NLO) properties, and density functional theory (DFT) calculations for three nickel diiminedithiolate complexes [Ni(4,4′-R2carboxy-bpy)(L)] [R = methyl, L = 1,2-benzenedithiolate (bdt), 1; R = ethyl, L = 5,6-dihydro-1,4-dithine-2,3-dithiolate (dddt), 2; R = ethyl, L = 1-(N-methylindol-5-yl)ethene-1,2-dithiolate (mi-5edt), 3]. The crystal structure of 1 shows a square-planar coordination for the nickel ion and bond distances consistent with a diiminedithiolate description for the complex. For all complexes, the cyclic voltammetry measurements show two reversible reduction processes (−1.353/–1.380 V and −0798/–0.830 V, respectively) and an anodic wave (+0.372/+0.601 V). The UV–vis spectra present a band around 600–700 nm (ε = 4880–6000 dm3 mol–1 cm–1) mainly attributed to a charge-transfer highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) transition, which shows a large negative solvatochromic shift, characteristic of push–pull complexes, and is responsible for the NLO properties of these molecules. The charge-transfer character of this electronic transition is confirmed by DFT calculations, with the HOMO mainly centered on the dithiolate moiety and the LUMO on the bpy ligand, with important contribution given by the carboxyl groups (≈13%). Small contributions from the nickel(II) ion are present in both of the frontier orbitals. The carboxyl groups enhance the optical properties of this class of complexes, confirmed by comparison with the corresponding unsubstituted compounds. The second-order NLO properties have been measured by an electric-field-induced second-harmonic-generation technique using a 10–3 M solution in N,N-dimethylformamide and working with a 1.907 μm incident wavelength, giving for μβ1.907 (μβ0) values of −1095 (−581), −2760 (−954), and −1650 (−618) × 10–48 esu for 1–3, respectively. These values are among the highest in the class of square-planar push–pull complexes, similar to those found for dithionedithiolate compounds. Moreover, spectroelectrochemical experiments demonstrate the possibility of using these complexes as redox-switchable NLO chromophores.
Co-reporter:Tracy E. Hewat, Lesley J. Yellowlees and Neil Robertson
Dalton Transactions 2014 vol. 43(Issue 10) pp:4127-4136
Publication Date(Web):24 Jan 2014
DOI:10.1039/C3DT53334D
Heteroleptic neutral copper(I) dipyrrin complexes have been synthesised with the general formula [Cu(4,4′-(R)-6,6′-(CH3)-bipyridine)(dipyrrin)], R = CH3 or CO2Et, and H-dipyrrin is either 1,3,7,9-tetramethyldipyrromethene (HL1), 1,13-diphenyl-6,8-diisoindolemethene (HL2), or 1,13-diphenyl-3,11-di(trifluoromethyl)-6,8-diisoindolemethene (HL3). Improved stability was observed across the series L1–L3, likely due to better steric constraints between the ligands. Visible light absorption has also been enhanced with a red-shift in absorption from 450 nm to 600 nm. Complex 3 shows photoluminescence lifetime in the order of nanoseconds suggesting singlet fluorescence which is supported by theoretical calculations. Study of the complexes as sensitisers in dye-sensitised solar cells was achieved by assembling the dye in situ on the surface of TiO2 in a series of steps (anchoring ligand followed by ancillary ligand and [Cu(CH3CN)4][BF4]. The highest efficiency achieved was 0.41% for the dye with HL3, attributed to better dye regeneration due to a more favourable oxidation potential.
Co-reporter:Miquel Planells, Maddalena Pizzotti, Gary S. Nichol, Francesca Tessore and Neil Robertson
Physical Chemistry Chemical Physics 2014 vol. 16(Issue 42) pp:23404-23411
Publication Date(Web):24 Sep 2014
DOI:10.1039/C4CP03509G
Tricyanofuran (TCF) derivatives attached to both anthracene and pyrene moieties were synthesised and characterised by optical, electrochemical and computational techniques. Both compounds exhibited similar absorption profile as well as electrochemical behaviour, however the pyrene derivative showed 20-fold higher non-linear optical activity measured by the EFISH technique. This huge difference has been assigned to (i) a lower molar absorption and (ii) a higher torsion angle for the anthracene derivative, confirmed by both experimental X-ray diffraction and DFT calculations. Furthermore, we note that the μβ1.907 value of −1700 × 10−48 esu recorded for the pyrene derivative in CHCl3/pyridine is remarkable for a NLO chromophore lacking a classical push–pull structure.
Co-reporter:Tracy Hewat, Shane McDonald, Jonathan Lee, Mahfujur Rahman, Petra Cameron, Fa-Chun Hu, Yun Chi, Lesley J. Yellowlees and Neil Robertson
RSC Advances 2014 vol. 4(Issue 20) pp:10165-10175
Publication Date(Web):07 Feb 2014
DOI:10.1039/C3RA47795A
Four simple ruthenium(II) dyes have been synthesised with the general formula [Ru(4,4′-(R,R1)-bipyridine)(4,4′-(R2,R3)-bipyridine)(NCS)2] where R, R1, R2 and R3 represent CH3 or CO2H, hence varying the number and position of the carboxylic acid groups that bind the dye to TiO2. The effect of varying the acid groups on cell fabrication, electrical performance and stability has been studied. The photophysical and electrochemical properties have been recorded and are relatively similar across the dye series, all showing parameters consistent with successful cell function, suggesting these dyes can be used as a good model to investigate the effect of changing the acid binding groups. Device measurements showed that the dyes containing a 4,4′-dicarboxy-bipyridine ligand, with two CO2H groups on the same bipy, gave higher short-circuit current than the dyes that had ligands with no more than one carboxylate group on a given bipy. Measurement of dye uptake on TiO2 using optical waveguide spectroscopy suggested that the dye with three acid groups provided better dye coverage, faster dye uptake rate, and a greater amount of dye remaining in the cell after rinsing. All four dyes gave cells that were broadly thermally stable at 85 °C over 500 hours, however the dye with only one acid group showed poorer thermal stability than the others.
Co-reporter:Miquel Planells;Efthymios Klampaftis;Martina Congiu;Ravichran Shivanna;K. Venkata Rao;Oleg Chepelin;Anita C. Jones;Bryce S. Richards;Subi J George;K. S. Narayan
European Journal of Inorganic Chemistry 2014 Volume 2014( Issue 19) pp:3095-3100
Publication Date(Web):
DOI:10.1002/ejic.201402228
Abstract
We describe the preparation and optical characterisation of a coronene tetracarboxylate salt (CS) in polyvinyl alcohol (PVA) thin film solutions processed from water, neat or mixed with varying ratios of a europium tris(hexafluoroacetylacetoanto) diaquo complex [Eu(hfac)3(H2O)2]. Neat CS-PVA showed not only well-defined fluorescence peaks but also a long-lived phosphorescence emission, persisting for more than 1 second. Interaction between the CS and EuIII molecules, mediated by means of carboxylate coordination to the EuIII, was attained by simple incorporation into the PVA polymer matrix and resulted in energy transfer from the coronone antenna to the europium centre. Under various blend ratios of CS and the EuIII complex, total photoluminescence quantum yields of typically around 30 % were achieved. The straightforward processing of this type of self-assembled chromophore-lanthanide system into a luminescent polymer film offers potential for application to other chromophores, lanthanides and polymers.
Co-reporter:Fa-Chun Hu;Sheng-Wei Wang; Yun Chi;Dr. Neil Robertson;Dr. Tracy Hewat;Yue Hu;Dr. Shih-Hung Liu; Pi-Tai Chou;Po-Fan Yang; Hao-Wu Lin
ChemPhysChem 2014 Volume 15( Issue 6) pp:1207-1215
Publication Date(Web):
DOI:10.1002/cphc.201300974
Abstract
To supplement our study on thiocyanate-free ruthenium sensitizers (TFRS) for dye-sensitized solar cells (DSSCs), which belong to a class of RuII-based complexes coordinated by a single 4,4′-dicarboxylic acid-2,2′-bipyridine and two symmetrically arranged functionalized trans-azolate chelates, we carefully isolated and characterized the second and less-abundant stereoisomer, in which the two pyridyl azolate ancillaries are asymetrically cis-arranged to each other. Two distinctive ancillaries, namely: 5-[4-(5-hexyl-2-thienyl)-2-pyridinyl]-3-trifluoromethyl pyrazole and 5-(6-tert-butyl-1-isoquinolinyl)-3-trifluoromethyl pyrazole, were employed in this study, giving a total of four sensitizers, that is, thienyl substituted TFRS-2 a and 2 b, and isoquinolinyl substituted TFRS-52 a and 52 b, in which the suffix b indicates the cis-stereoisomers. To gain insight into their fundamental properties their photophysical, electrochemical, and spectroelectrochemical behavior was investigated by density functional theory. Upon comparison of the correspondingly fabricated DSSCs, the sensitizers TFRS-2 a and 52 a yielded significantly higher conversion efficiencies than their asymmetrical cis-counterparts, TFRS-2 b and 52 b. To rationalize the cell performances charge extraction/photovoltage decay and impedance spectroscopic measurements were carried out to compare the rates of interfacial electron recombination from the TiO2 conduction band to the electrolyte.
Co-reporter:Miquel Planells, Antonio Abate, Derek J. Hollman, Samuel D. Stranks, Vishal Bharti, Jitender Gaur, Dibyajyoti Mohanty, Suresh Chand, Henry J. Snaith and Neil Robertson
Journal of Materials Chemistry A 2013 vol. 1(Issue 23) pp:6949-6960
Publication Date(Web):01 May 2013
DOI:10.1039/C3TA11417A
We have synthesized and characterized a series of triphenylamine-based hole-transport materials (HTMs), and studied their function in solid-state dye sensitized solar cells (ss-DSSCs). By increasing the electron-donating strength of functional groups (–H < –Me < –SMe < –OMe) we have systematically shifted the oxidation potential and ensuing photocurrent generation and open-circuit voltage of the solar cells. Correlating the electronic properties of the HTM to the device operation highlights a significant energy offset required between the Dye – HTM highest occupied molecular orbital (HOMO) energy levels. From this study, it is apparent that precise control and tuning of the oxidation potential is a necessity, and usually not achieved with most HTMs developed to date for ss-DSSCs. To significantly increase the efficiency of solid-state DSSCs understanding these properties, and implementing dye-HTM combinations to minimize the required HOMO offset is of central importance.
Co-reporter:Martina Congiu, Mohamed Alamiry, Omar Moudam, Serena Ciorba, Patricia R. Richardson, Laurent Maron, Anita C. Jones, Bryce S. Richards and Neil Robertson
Dalton Transactions 2013 vol. 42(Issue 37) pp:13537-13545
Publication Date(Web):30 Jul 2013
DOI:10.1039/C3DT51380G
Synthesis and photophysical characterisation of [Ln(hfac)3DPEPO] complexes (with Ln = Eu, Tb, Yb, Nd, Gd) has been carried out to investigate the factors responsible for the variation in total photoluminescence quantum yield within this family of emissive lanthanide complexes. Electronic absorption and emission spectroscopy, in conjunction with DFT calculations of the excited state of the Eu complex, elucidate the role of each ligand in the sensitisation of the lanthanide through the antenna effect. The X-ray crystal structure of [Gd(hfac)3DPEPO] has been determined and shows an 8-coordinate environment around the Gd and a ten-membered chelate ring involving the DPEPO ligand. Total photoluminescence quantum yields were measured to be 6%, 1% and 2% for Ln = Tb, Nd and Yb, respectively, in comparison with around 80% for Ln = Eu. The lower quantum yield for Nd and Yb, compared with Eu, can be attributed to more efficient quenching of the excited Ln state by high-energy oscillations within the ligands, whereas the lower quantum yield for Tb is assigned to a combination of poor energy transfer from the ligand excited state to the Tb and longer radiative lifetime.
Co-reporter:Sushobhan Ghosh, Georg T. Silber, Andrew J. P. White, Neil Robertson and Ramon Vilar
Dalton Transactions 2013 vol. 42(Issue 38) pp:13813-13816
Publication Date(Web):12 Aug 2013
DOI:10.1039/C3DT51845K
The synthesis of a terpyridine–guanosine ligand and its reaction with copper(II) to yield a new [2 + 2] metallo-rectangle is reported. The metallo-rectangle was characterized by single crystal X-ray diffraction and the structure showed significant intramolecular π–π stacking interactions between the two terpyridine moieties of the molecule. This prompted us to investigate the magnetic properties of the new di-copper(II) assembly which displayed ferromagnetic interactions in the solid state.
Co-reporter:Miquel Planells, Luke X. Reynolds, Umesh Bansode, Shraddha Chhatre, Satishchandra Ogale, Neil Robertson and Saif A. Haque
Physical Chemistry Chemical Physics 2013 vol. 15(Issue 20) pp:7679-7684
Publication Date(Web):17 Apr 2013
DOI:10.1039/C3CP50980J
We report the synthesis and optical characterisation of different triphenylamine-based hole capture materials able to anchor to CdSe quantum dots (QDs). Cyclic voltammetry studies indicate that these materials exhibit reversible electrochemical behaviour. Photoluminescence and transient absorption spectroscopy techniques are used to study interfacial charge transfer properties of the triphenylamine functionalized CdSe QDs. Specifically, we show that the functionalized QDs based on the most easily oxidised triphenylamine display efficient hole-extraction and long-lived charge separation. The present findings should help identify new strategies to control charge transfer QD-based optoelectronic devices.
Co-reporter:Fa-Chun Hu;Sheng-Wei Wang;Dr. Miquel Planells;Dr. Neil Robertson;Dr. Harihara Padhy;Bo-Sian Du;Dr. Yun Chi;Po-Fan Yang;Dr. Hao-Wu Lin;Dr. Gene-Hsiang Lee;Dr. Pi-Tai Chou
ChemSusChem 2013 Volume 6( Issue 8) pp:1366-1375
Publication Date(Web):
DOI:10.1002/cssc.201300417
Abstract
A series of OsII sensitizers (TFOS-x, in which x=1, 2, or 3) with a single 4,4′-dicarboxy-2,2′-dipyridine (H2dcbpy) anchor and two chelating 2-pyridyl (or 2-pyrimidyl) triazolate ancillaries was successfully prepared. Single-crystal X-ray structural analysis showed that the core geometry of the OsII-based sensitizers consisted of one H2dcbpy unit and two eclipsed cis-triazolate fragments; this was notably different from the RuII-based counterparts, in which the azolate (both pyrazolate and triazolate) fragments are located at the mutual trans-positions. The basic properties were extensively probed by using spectroscopic and electrochemical methods as well as time-dependent density functional theory (TD-DFT) calculations. Fabrication of dye-sensitized solar cells (DSCs) was then attempted by using the I−/I3−-based electrolyte solution. One such DSC device, which utilized TFOS-2 as the sensitizer, showed promising performance characteristics with a short-circuit current density (JSC) of 15.7 mA cm−2, an open-circuit voltage of 610 mV, a fill factor of 0.63, and a power conversion efficiency of 6.08 % under AM 1.5G simulated one-sun irradiation. Importantly, adequate incident photon-to-current conversion efficiency performances were observed for all TFOS derivatives over the wide spectral region of 450 to 950 nm, showing a panchromatic light harvesting capability that extended into the near-infrared regime. Our results underlined a feasible strategy for maximizing JSC and increasing the efficiency of DSCs.
Co-reporter:Alexander M. Whyte, Yoshiaki Shuku, Gary S. Nichol, Michio M. Matsushita, Kunio Awaga and Neil Robertson
Journal of Materials Chemistry A 2012 vol. 22(Issue 34) pp:17967-17975
Publication Date(Web):30 Jul 2012
DOI:10.1039/C2JM33079B
A series of planar Ni(II), Cu(II) and Co(II) tetraaza[14]annulenes has been prepared and studied optically, electrochemically and magnetically. Thin films of each of these complexes have been prepared by vacuum deposition to evaluate the field-effect transistor (FET) performance as well as the morphology and crystallinity of the film formed. The electrochemistry and UV/Vis absorption studies indicate the materials are redox active and highly coloured, with molar extinction coefficients as large as 80000 M−1 cm−1 in the visible region. The paramagnetic complexes display weak antiferromagnetic interactions, fit to the Bonner–Fisher chain model. Each of the materials formed polycrystalline films when vacuum deposited and showed field-effect transistor behaviour, with charge carrier mobilities in the range of 10−5 to 10−9 cm2 V−1 s−1. SEM imaging of the substrates indicates that the central metal ion, and its sublimation temperature, has a crucial role in defining the morphology of the resulting film.
Co-reporter:Miquel Planells
European Journal of Organic Chemistry 2012 Volume 2012( Issue 26) pp:4947-4953
Publication Date(Web):
DOI:10.1002/ejoc.201200715
Abstract
A series of unsymmetrical dyes containing a naphthyl unit connected to an electron acceptor moiety was designed and synthesised. By modifying the electron acceptor unit, a shift of the LUMO energy level as well as its distribution through the molecule were achieved. These dyes were fully characterised by optical, computational and electrochemical techniques. In addition, crystal structures reveal different packing depending upon the nature of the acceptor. Their potential use as electron acceptor materials for organic photovoltaics (OPVs) was also investigated by photoluminescence studies of blends with the common OPV polymers P3HT and PCDTBT.
Co-reporter:Robert A. Valentine, Alexander Whyte, Kunio Awaga, Neil Robertson
Tetrahedron Letters 2012 Volume 53(Issue 6) pp:657-660
Publication Date(Web):8 February 2012
DOI:10.1016/j.tetlet.2011.11.124
We have prepared two new C3-symmetric, substituted-triazatruxene molecules using a facile one-pot trimerisation of 5-carboxyindole and 6-bromoindole in acetic acid using Br2, giving 2a and 3a, respectively. These were subsequently modified by the addition of six alkyl chains to the N- and carboxyl-positions of 2a giving 2b and three alkyl chains to the N-positions of 3a giving 3b. The new molecules were characterised using cyclic voltammetry, UV/vis and emission spectroscopy, DFT calculations and in the case of 3b, field-effect transistor measurements showing gate-modulated source-drain current. These represent a straightforward route to large polyaromatic molecules with easily-modified side groups and are suitable as building blocks for synthesis of functional molecules for materials.
Co-reporter:Simon Dalgleish, Hirofumi Yoshikawa, Michio M. Matsushita, Kunio Awaga and Neil Robertson
Chemical Science 2011 vol. 2(Issue 2) pp:316-320
Publication Date(Web):29 Oct 2010
DOI:10.1039/C0SC00446D
Electrooxidation to form neutral films of a homoleptic nickel dithiolene [Ni(b-3ted)2] (1) from an air-stable TBA salt is described [b-3ted = bis(3-thienyl)-1,2-ethylenedithiolene; TBA = tetrabutylammonium]. Films grown by potentiostatic electrodeposition directly onto interdigitated electrode arrays show improved conductivity compared to those formed by solution methods. The grown films are free from residual electrolyte doping, and this technique is shown to yield robust films of reproducible electronic performance. The conductivity of films formed by electrodeposition show gate dependence when grown directly onto field effect transistor substrates. Thin-film X-ray diffraction confirms the electrodeposited films to be of the same polymorph as films and single crystals formed by solution methods. Scanning electron microscopy shows the electrodeposited films to have larger, more connected polycrystalline regions, as well as improved contact with the electrodes.
Co-reporter:Simon Dalgleish, John G. Labram, Zhe Li, Jianpu Wang, Christopher R. McNeill, Thomas D. Anthopoulos, Neil C. Greenham and Neil Robertson
Journal of Materials Chemistry A 2011 vol. 21(Issue 39) pp:15422-15430
Publication Date(Web):05 Sep 2011
DOI:10.1039/C1JM12466H
The synthesis and full characterisation of a novel indole-substituted nickel dithiolene [Ni(mi-5edt)2] (3) is reported, and compared to its alkyl-substituted analogue [Ni(mi-5hdt)2] (4) that has been previously communicated [Dalgleish et al., Chem. Commun., 2009, 5826] [mi-5edt = 1-(N-methylindol-5-yl)-ethene-1,2-dithiolate; mi-5hdt = 1-(N-methylindol-5-yl)-hex-1-ene-1,2-dithiolate)]. Both complexes are shown to undergo oxidative electropolymerisation, yielding polymer films that retain the redox and optical properties of the monomer. The more soluble analogue 4 is shown to form high quality thin films by spin coating, which have been utilised to fabricate field-effect transistors (FETs) and bulk heterojunction photovoltaic devices (BHJ-PVs). From FET studies, the material shows ambipolar charge transport behaviour, with a maximum carrier mobility of ∼10−6 cm2 V−1s−1 for electrons. By using 4 simultaneously as the electron acceptor as well as a NIR sensitiser in BHJ-PVs, the complex is shown to contribute to the photocurrent, extending light harvesting into the NIR region.
Co-reporter:Simon Dalgleish, Kunio Awaga and Neil Robertson
Chemical Communications 2011 vol. 47(Issue 25) pp:7089-7091
Publication Date(Web):27 May 2011
DOI:10.1039/C1CC12344K
Thin films of neutral copper dithiolenes have been prepared by potentiostatic electrodeposition. This method allows the isolation of near infrared (NIR) active species, in a useable form, that are otherwise unobtainable by conventional chemical methods.
Co-reporter:Alexander M. Whyte, Benjamin Roach, David K. Henderson, Peter A. Tasker, Michio M. Matsushita, Kunio Awaga, Fraser J. White, Patricia Richardson, and Neil Robertson
Inorganic Chemistry 2011 Volume 50(Issue 24) pp:12867-12876
Publication Date(Web):November 18, 2011
DOI:10.1021/ic2020644
Square planar complexes of the type Ni(L1)2, Ni(L2)2, Cu(L1)2, and Cu(L2)2, where L1H = 2-hydroxy-5-t-octylacetophenone oxime and L2H = 2-hydroxy-5-n-propylacetophenone oxime, have been prepared and characterized by single-crystal X-ray diffraction, cyclic voltammetry, UV/vis spectroscopy, field-effect-transistor measurements, density functional theory (DFT) and time-dependent DFT (TDDFT) calculations, and, in the case of the paramagnetic species, electron paramagnetic resonance (EPR) and magnetic susceptibility. Variation of alkyl groups on the ligand from t-octyl to n-propyl enabled electronic isolation of the complexes in the crystal structures of M(L1)2 contrasting with π-stacking interactions for M(L2)2 (M = Ni, Cu). This was evidenced by a one-dimensional antiferromagnetic chain for Cu(L2)2 but ideal paramagnetic behavior for Cu(L1)2 down to 1.8 K. Despite isostructural single crystal structures for M(L2)2, thin-film X-ray diffraction and scanning electron microscopy (SEM) revealed different morphologies depending on the metal and the deposition method (vapor or solution). The Cu complexes displayed limited electronic interaction between the central metal and the delocalized ligands, with more mixing in the case of Ni(II), as shown by electrochemistry and UV/vis spectroscopy. The complexes M(L2)2 showed poor charge transport in a field-effect transistor (FET) device despite the ability to form π-stacking structures, and this provides design insights for metal complexes to be used in conductive thin-film devices.
Co-reporter:Duncan Wass and Neil Robertson
Dalton Transactions 2011 vol. 40(Issue 15) pp:3775-3776
Publication Date(Web):22 Mar 2011
DOI:10.1039/C1DT90027G
A graphical abstract is available for this content
Co-reporter:Charlotte L. Linfoot, Patricia Richardson, Keri L. McCall, James R. Durrant, Ana Morandeira, Neil Robertson
Solar Energy 2011 Volume 85(Issue 6) pp:1195-1203
Publication Date(Web):June 2011
DOI:10.1016/j.solener.2011.02.023
We report the first example of a Ni(II) complex that demonstrates sensitiser function in a Dye-Sensitised Solar Cell (DSSC). Complexes [Ni(dcbpy)(qdt)] (1), [Ni(decbpy)(qdt)] (2) and [Ni(decbpy)Cl2] (3) (where dcbpy = 4,4′-dicarboxy-2,2′-bipyridine; decbpy = 4,4′-di(CO2Et)-2,2′-bipyridine; and qdt = quinoxaline-2,3-dithiolate) have been prepared. Characterisation was carried out using electrochemical, spectroscopic and computational techniques. Intensive visible transitions of 1 and 2 have been assigned predominantly to Ligand-to-Ligand Charge Transfer (LLCT) from the qdt to the diimine ligand, suggesting appropriate charge separation for application in a photoelectrochemical device. TiO2 sensitised with 2, following charge injection, processes a recombination time significantly long for photovoltaic function. In a DSSC, using I-/I3- redox electrolyte, photocurrents and photovoltages of 0.293 mA and 521 mV were observed, with optimum values requiring TiCl4 post-treatment of TiO2 and co-adsorption of Chenodeoxycholic acid (Cheno). Although photovoltaic function was observed, the low photocurrent is attributed to a short-lived excited state lifetime resulting in poor charge injection from the Ni(II) sensitiser.
Co-reporter:Keri L. McCall;James R. Jennings;Hongxia Wang;Ana Moreira;Laurence M. Peter;James R. Durrant;Lesley J. Yellowlees
European Journal of Inorganic Chemistry 2011 Volume 2011( Issue 4) pp:589-596
Publication Date(Web):
DOI:10.1002/ejic.201001039
Abstract
We prepared the complexes [Ru{4,4′-(CO2R-bpy)2}{Cu(exoO2-cyclam)}][NO3]2 [R = Et (1), H (2)], which possess a CuII centre covalently linked to a (bipyridyl)RuII fragment. The complexes were characterised by cyclic voltammetry, UV/Vis spectroscopy, hybrid DFT and TD-DFT (time-dependent density-functional theory) calculations, EPR (electron paramagnetic resonance), emission spectroscopy and UV/Vis spectroelectrochemistry, with the latter showing reversible conversion to the mono- and di-oxidised and mono- and di-reduced species. The data suggest the first oxidation to be largely based on the Ru centre but with little energetic difference between the highest occupied orbitals based on Ru and based on Cu. There was also evidence of solvent coordination in both the electrochemistry and spectroelectrochemistry experiments. The redox potentials and the strongvisible absorptions of 2 (λmax = 562 nm, ϵmax = 22200 M–1 cm–1)make it appropriate for study as a sensitiser in a dye-sensitised solar cell. Charge-separated lifetime of photoexcited 2 on TiO2 and incident photon-to-current conversion efficiency (IPCE) as a function of wavelength were studied and are discussed alongside the formation of dye-sensitised solar cells with the best efficiency achieved of η = 2.55 %, Voc = 608 mV, Isc = 5.84 mA cm–2 and ff = 0.72. Limitations to the maximum efficiency obtained were attributed to a mismatch between the bipyridyl-based unoccupied orbital of the dye and the TiO2 conduction band edge.
Co-reporter:Simon Dalgleish, Neil Robertson
Coordination Chemistry Reviews 2010 Volume 254(13–14) pp:1549-1558
Publication Date(Web):July 2010
DOI:10.1016/j.ccr.2009.10.022
The emerging field of polymerisable metal dithiolenes, where one or more of the ligands is capable of covalently linking to another, is discussed and the physical and electronic properties of the molecular and polymeric materials compared. Materials that display both the interesting redox and optical properties of metal dithiolenes, whilst possessing the enhanced stability and electronic communication of an organic polymer framework, would find widespread application in many areas of materials science. The rational design of such materials is therefore of key importance in the production of new dithiolene containing functional materials for the development of novel multi-functional devices. Although the field is currently small, many interesting observations have already been made that allowed us to relate aspects of structure to function. In particular, the redox and optical properties appear to be strongly dependent on the linking positions within the polymer, imposed by the ligand design, and able to be tuned through strategies such as copolymerisation.
Co-reporter:Dimitrios Maganas, Alexios Grigoropoulos, Sarah S. Staniland, Spyros D. Chatziefthimiou, Andrew Harrison, Neil Robertson, Panayotis Kyritsis and Frank Neese
Inorganic Chemistry 2010 Volume 49(Issue 11) pp:5079-5093
Publication Date(Web):May 12, 2010
DOI:10.1021/ic100163g
Sulfur-containing mono- or bidentate types of ligands, usually form square planar Ni(II)S4 complexes. However, it has already been established that the bidentate L− dithioimidodiphosphinato ligands, [R2P(S)NP(S)R′2]−, R, and R′ = aryl or alkyl, can afford both tetrahedral and square planar, NiS4-containing, homoleptic NiR,R′L2 complexes, owing to an apparent structural flexibility, which has not, so far, been probed. In this work, the literature tetrahedral Ni[R2P(S)NP(S)R2]2 complexes, R = Ph (NiPh,PhL2, 1Td) and R = iPr (NiiPr,iPrL2, 2) as well as the newly synthesized Ni[iPr2P(S)NP(S)Ph2]2 complex (NiiPr,PhL2, 3), have been studied by UV−vis, IR, and 31P NMR spectroscopy. Complex 3 was shown by X-ray crystallography to be square planar, and magnetic studies confirmed that it is diamagnetic in the solid state. However, it becomes paramagnetic in solution, as it shows a similar UV−vis spectrum to one of the tetrahedral 1Td and 2 complexes. The crystal structure of the potassium salt of the asymmetric ligand, [iPr2P(S)NP(S)Ph2]K, has also been determined and compared to those of the protonated iPr2P(S)NHP(S)Ph2 ligand and complex 3. All three, 1Td, 2, and 3, NiR,R′L2 complexes show strong paramagnetic effects in their solution 31P NMR spectra. The magnetic properties of paramagnetic complexes 1 and 2 in the solid state were investigated on oriented crystals, and their analysis afforded remarkably small values of the spin−orbit coupling constant (λ) and orbital reduction factor (k) parameters, implying significant delocalization of unpaired electronic density toward the ligands. The above experimental findings are combined with data from standard density functional theory and correlated multiconfiguration ab initio theoretical methods, in an effort to investigate the interplay between the square planar and tetrahedral geometries of the NiS4 core, the mechanistic pathway for the spin-state interconversion, the degree of covalency of the Ni−S bonds, and the distribution of the spin density in this type of system. The analysis provides justification for the structural flexibility of such ligands, affording NiR,R′L2 complexes with variable metallacycle conformation and NiS4 core geometries. Of particular importance are the large zero-field splitting values estimated by both experimental and theoretical means, which have not, as yet, been verified by direct methods, such as electron paramagnetic resonance spectroscopy. The findings of our work confirm earlier observations on the feasibility of synthesizing either tetrahedral or square planar NiS4 complexes containing the same type of ligands. They can also form the basis of investigating structure−properties relationships in other NiS4-containing systems.
Co-reporter:Charlotte L. Linfoot, Patricia Richardson, Tracy E. Hewat, Omar Moudam, Michael M. Forde, Anna Collins, Fraser White and Neil Robertson
Dalton Transactions 2010 vol. 39(Issue 38) pp:8945-8956
Publication Date(Web):21 Sep 2010
DOI:10.1039/C0DT00190B
The synthesis and subsequent spectroscopic, electrochemical, photophysical and computational characterisation of a series of heteroleptic Cu(I) complexes of general formula: [CuPOP{4,4′(R)-bipyridyl}][BF4] and [CuPOP{4,4′,6,6′(R)-bipyridyl}][BF4] is described (POP = bis{2-(diphenylphosphanyl)phenyl} ether; R = Me, CO2H, CO2Et. The steric constraint imposed by the POP ligand can impede distortion towards square planar geometry upon MLCT excitation or oxidation and this is explored in the context of varying substituents on the bipyridyl ligand. The insight gained opens new avenues for design of functional Cu(I) systems suitable for photophysical and photoelectrochemical applications such as sensitisers for dye-sensitised solar cells (DSSCs).
Co-reporter:Keri L. McCall, Ana Morandeira, James Durrant, Lesley J. Yellowlees and Neil Robertson
Dalton Transactions 2010 vol. 39(Issue 17) pp:4138-4145
Publication Date(Web):18 Mar 2010
DOI:10.1039/B924660F
The control of the loss mechanism in a dye sensitised solar cell (DSSC) via recombination of the injected electron with the oxidised dye was investigated by incorporating a redox-active ligand, 6,7-bis(methylthio)tetrathiafulvalene dithiolate (TTF(SMe)2), into a ruthenium bipyridyl dye. A series of dyes with general formula [Ru(4,4′-R-bpy)2(TTF(SMe)2], where R = H, CO2Et and CO2H, were synthesised and characterised using electrochemistry, absorption and emission spectroscopy, spectroelectrochemistry and hybrid-DFT calculations. In addition, the performance of the acid derivative in a DSSC was investigated using IV measurements, as well as transient absorption spectroscopy. These complexes showed significant TTF-ligand character to the HOMO orbital, as deduced by spectroelectrochemical, emission and computational studies. Upon adsorption of the acid derivative to TiO2 a long-lived charge-separated state of 20 ms was observed via transient absorption spectroscopy. Despite this long-lived charge-separated state, the dye yielded extremely low DSSC efficiencies, attributed to the poor regeneration of the neutral dye by iodide. As a result, the complex forms a novel long-lived charge separated state that persists even under working solar cell electrolyte conditions.
Co-reporter:Simon Dalgleish, Carole A. Morrison, Derek S. Middlemiss, Andrew R. Mount, Anna Collins, Luca Pilia, Angela Serpe, M. Laura Mercuri, Susan J. Roberts-Bleming, Adam Charlton, Paola Deplano, Patrick J. Murphy and Neil Robertson
Journal of Materials Chemistry A 2009 vol. 19(Issue 34) pp:6194-6200
Publication Date(Web):08 Jul 2009
DOI:10.1039/B907028A
The synthesis, structure and spectroscopic properties of a new class of asymmetric nickel dithiolene complex containing pendent thiophene units [Ni(R2pipdt)(b-3ted)] are described {R = Bz (3), iPr (4); pipdt = piperazine-3,2-dithione; b-3ted = bis(3-thienyl)-1,2-ethylenedithiolene}. X-ray crystallography of both neutral species shows planar nickel dithiolene units and the thiophene groups twisted out of the molecular plane, with the R group having a large effect on the packing structure. DFT geometry calculations show good agreement with experimental data for 3 and 4 and confirm that the low energy absorption, assigned to a HOMO → LUMO transition, is inter-ligand charge-transfer in character. Solid state calculations show greater band dispersion in 4, which corresponds to a closer packing in the crystal lattice. Cyclic voltammetry of both complexes displays three reversible processes, corresponding to an interconversion between cationic, neutral, anionic and dianionic species, with tuning of the redox potentials by variation of the R group. Electrochemical polymerisation of 3 shows incorporation of intact dithiolene units into a polymer film with redox functionality similar to that of the monomer, whereas co-polymerisation of 3 with thiophene yields a highly conductive film with redox functionality similar to polythiophene and enhanced absorption across the near IR.
Co-reporter:Simon Dalgleish and Neil Robertson
Chemical Communications 2009 (Issue 39) pp:5826-5828
Publication Date(Web):09 Sep 2009
DOI:10.1039/B913174D
A novel nickel dithiolene-containing polymer, generated by the electropolymerisation of pendent indole units, has been prepared and shows good stability and fast reversible switching of the near infrared absorption by varying the applied potential of the film.
Co-reporter:Omar Moudam, Brenda C. Rowan, Mohammed Alamiry, Patricia Richardson, Bryce S. Richards, Anita C. Jones and Neil Robertson
Chemical Communications 2009 (Issue 43) pp:6649-6651
Publication Date(Web):25 Sep 2009
DOI:10.1039/B914978C
We have prepared complexes of formula [Eu(β-diketonate)3(DPEPO)] and shown quantitative excited-state energy transfer from the ligands combined with efficient Ln luminescence leading to exceptionally-high total photoluminescence quantum yield of up to 80% in solution and in PMMA.
Co-reporter:Keri L. McCall, James R. Jennings, Hongxia Wang, Ana Morandeira, Laurence M. Peter, James R. Durrant, Lesley J. Yellowlees, J. Derek Woollins, Neil Robertson
Journal of Photochemistry and Photobiology A: Chemistry 2009 Volume 202(2–3) pp:196-204
Publication Date(Web):25 February 2009
DOI:10.1016/j.jphotochem.2008.11.022
Two series of novel ruthenium bipyridyl dyes incorporating sulfur-donor bidentate ligands with general formula [Ru(R-bpy)2C2N2S2] and [Ru(R-bpy)2(S2COEt)][NO3] (where R = H, CO2Et, CO2H; C2N2S2 = cyanodithioimidocarbonate and S2COEt = ethyl xanthogenate) have been synthesized and characterized spectroscopically, electrochemically and computationally. The acid derivatives in both series (C2N2S23 and S2COEt 6) were used as a photosensitizer in a dye-sensitized solar cell (DSSC) and the incident photo-to-current conversion efficiency (IPCE), overall efficiency (η) and kinetics of the dye/TiO2 system were investigated. It was found that 6 gave a higher efficiency cell than 3 despite the latter dye's more favorable electronic properties, such as greater absorption range, higher molar extinction coefficient and large degree of delocalization of the HOMO. The transient absorption spectroscopy studies revealed that the recombination kinetics of 3 were unexpectedly fast, which was attributed to the terminal CN on the ligand binding to the TiO2, as evidenced by an absorption study of R = H and CO2Et dyes sensitized on TiO2, and hence leading to a lower efficiency DSSC.
Co-reporter:Lucy P. Moorcraft, Lorna A. Jack, James R. Jennings, Laurence M. Peter, Lesley J. Yellowlees, Neil Robertson
Polyhedron 2009 28(18) pp: 4084-4090
Publication Date(Web):
DOI:10.1016/j.poly.2009.09.017
Co-reporter:Tania Anjos, Susan J. Roberts-Bleming, Adam Charlton, Neil Robertson, Andrew R. Mount, Simon J. Coles, Michael B. Hursthouse, Maher Kalaji and Patrick J. Murphy
Journal of Materials Chemistry A 2008 vol. 18(Issue 4) pp:475-483
Publication Date(Web):07 Dec 2007
DOI:10.1039/B714372A
The synthesis, electrochemical and spectroscopic properties of the new thiophene-substituted metal dithiolene complexes [Ni(b-3ted)2] (3) and [NBu4][Ni(b-3ted)2] ([NBu4][3]) are described [b-3ted = bis(3-thienyl)-1,2-ethylenedithiolene] and compared with new studies of the known compounds [Ni(b-2ted)2] (2) and [NBu4][Ni(b-2ted)2] ([NBu4][2]). X-Ray structures were determined for the neutral complexes 2 and 3 and both showed planar nickel dithiolene units with thiophene groups twisted out of the molecular plane, precluding close molecular π-stacking. Electrochemical investigations revealed two redox processes corresponding to interconversion between neutral, monoanionic and dianionic species for 3, analogous to 2. Oxidation of 0.1 mM [3]− in CH3CN was shown to give a green molecular film of 3 which, in contrast to as-prepared crystals of 3, showed significant conductivity. Electrochemical polymerisation of 3 carried out at different concentrations resulted in films; electrochemical, SNIFTIRS and UV-Vis results were consistent with incorporation of the intact metal dithiolene complex in these films. In contrast, electrochemical polymerisation of 2 gave a film charateristic of a polymerised thiophene but with no evidence of incorporation of the intact metal dithiolene complex. Copolymerisation of 3 with thiophene gave a gold-coloured electropolymerised film of significant conductivity that, upon dissolution in CH2Cl2, showed the characteristic low energy absorption of the Ni-dithiolene complex, confirming its incorporation. This copolymerisation approach offers a versatile route to the synthesis of metal dithiolene–polythiophene hybrid films.
Co-reporter:Elaine A. M. Geary, Keri L. McCall, Andrew Turner, Paul R. Murray, Eric J. L. McInnes, Lorna A. Jack, Lesley J. Yellowlees and Neil Robertson
Dalton Transactions 2008 (Issue 28) pp:3701-3708
Publication Date(Web):29 May 2008
DOI:10.1039/B719789F
A series of [Pt(II)(diimine)(dithiolate)] complexes of general formula [Pt{X,X′-(CO2R)2-bpy}(mnt)] (where X = 3, 4 or 5; R = H or Et, bpy = 2,2′-bipyridyl and mnt = maleonitriledithiolate), have been spectroscopically, electrochemically and computationally characterised and compared with the precursors [Pt{X,X′-(CO2R)2-bpy}Cl2] and X,X′-(CO2R)2-bpy. The study includes cyclic voltammetry, in situEPR spectroelectrochemical studies of fluid solution and frozen solution samples, UV/Vis/NIR spectroelectrochemistry, hyrid DFT and TD-DFT calculations. The effect of changing the position of the bpy substituents from 3,3′ to 4,4′ and 5,5′ is discussed with reference to electronic changes seen within the different members of the family of molecules. The performance of the mnt complexes in dye-sensitised solar cells has been previously described and the superior performance of [Pt{3,3′-(CO2R)2-bpy}(mnt)] is now explained in terms of decreased electronic delocalisation through twisting of the bipyridyl ligand as supported by the EPR and computational results.
Co-reporter:Lucy P. Moorcraft, Ana Morandeira, James R. Durrant, James R. Jennings, Laurence M. Peter, Simon Parsons, Andrew Turner, Lesley J. Yellowlees and Neil Robertson
Dalton Transactions 2008 (Issue 48) pp:6940-6947
Publication Date(Web):03 Nov 2008
DOI:10.1039/B811943K
The dye complexes [Pt(4-CO2R-py)2(mnt)] (R = H (3a), CH3 (3b)) and the precursor complexes [Pt(4-CO2R-py)2Cl2] (2a, 2b) (py = pyridyl) were synthesised, characterised by electrochemical, spectroscopic, spectroelectrochemical (UV-vis-nIR and in situEPR) and hybrid DFT computational methods and attached to a TiO2 substrate to determine charge recombination kinetics. The results were compared to the bipyridyl analogues [Pt{X,X′-(CO2R)-2,2′-bipyridyl}(mnt)], (X = 3 or 4). The electronic characteristics of the bis-pyridyl complex were found to be different to the bipyridyl complexes making the former harder to reduce, shifting the lowest-energy absorption band to higher energy and showing separate degenerate LUMO orbitals on the two pyridine rings. The latter point determines that the di-reduced pyridyl complex remains EPR active, unlike the bipyridyl analogue. Complex 3a attached to nanocrystalline TiO2 shows a long charge recombination lifetime in comparison with the analogous complex with the ubiquitous 4,4′-(CO2H)2-bipyridyl ligand, suggesting that pyridyl complexes may possess some advantage over bipyridyl complexes in dye-sensitised solar cells.
Co-reporter:Kunio Awaga, Yoshikatsu Umezono, Wataru Fujita, Hirofumi Yoshikawa, HengBo Cui, Hayao Kobayashi, Sarah S. Staniland, Neil Robertson
Inorganica Chimica Acta 2008 Volume 361(14–15) pp:3761-3770
Publication Date(Web):1 October 2008
DOI:10.1016/j.ica.2008.03.065
We have examined the crystal structures and the electrical and magnetic properties of the molecular compounds of a thiazyl radical, 1,3,2-benzodithiazolyl (abbreviated as BDTA). BDTA was found to be a useful building block for molecular conductors and magnets because it can operate as a counter cation, a donor or a ligand, depending on its charge. (i) A charge-transfer complex, [BDTA][TCNQ], crystallizes into a uniform segregated stacking structure with a short contact between the donor and acceptor columns. In spite of the partial charge transfer between the two components, this complex exhibits semiconductive behaviour, probably due to a large electron correlation on BDTA. (ii) The crystal structure of [BDTA][Ni(mnt)2] (mnt = maleonitriledithiolate) consists of alternating stacking columns of S = 0 [BDTA]+ and S = 1/2 [Ni(mnt)2]−, in which a ferromagnetic coupling operates between the [Ni(mnt)2]− anions through the [BDTA] + cation. (iii) [BDTA]2[Cu(mnt)2] consists of an alternating stack of a head-to-head [BDTA]+ dimer and a planar [Cu(mnt)2]2− dianion. Short intermolecular S⋯S contacts between the stacks give rise to an ideal 1D Heisenberg antiferromagnetic chain of [Cu(mnt)2]2− with a coupling constant of J/kB = 16–17 K. (iv) The crystal structure of [BDTA]2[Co(mnt)2] is similar to that of [BDTA]2[Cu(mnt)2] at 253 K, but this salt undergoes a phase transition at 190 K, below which a partial electron transfer occurs from [Co(mnt)2]2− to one of the [BDTA]+ cations along with formation of a coordination bond. (v) [BDTA][Ni(dmit)2]2 (dmit = 1,3-dithiol-2-thione-4,5-dithiolate) exhibits room-temperature conductivity of 0.1 S cm−1 and semiconductive behaviour over the range 80–200 K, which can be interpreted in terms of multi-conducting bands.A thiazyl radical, 1,3,2-benzodithiazolyl is a useful building block for molecular conductors and magnets because it can operate as a counter cation, a donor or a ligand. We report semiconductive behaviour, ferromagnetic coupling, ideal 1D Heisenberg chain, charge-transfer phase transition and multi-conducting band system in the BDTA complexes of TCNQ, [M(mnt)2] (M = Co, Ni, Cu), and [Ni(dmit)2].
Co-reporter:Neil Robertson
Angewandte Chemie International Edition 2008 Volume 47( Issue 6) pp:1012-1014
Publication Date(Web):
DOI:10.1002/anie.200704538
Co-reporter:Neil Robertson
Angewandte Chemie 2008 Volume 120( Issue 6) pp:1028-1030
Publication Date(Web):
DOI:10.1002/ange.200704538
Co-reporter:Neil Robertson Dr.
ChemSusChem 2008 Volume 1( Issue 12) pp:977-979
Publication Date(Web):
DOI:10.1002/cssc.200800214
Co-reporter:Vivienne A. White, Russell D. L. Johnstone, Keri L. McCall, Nicholas J. Long, Alexandra M. Z. Slawin and Neil Robertson
Dalton Transactions 2007 (Issue 27) pp:2942-2948
Publication Date(Web):10 May 2007
DOI:10.1039/B701166K
Complexes of the ligand 2,3-dioxo-1,4,8,11-tetraaza-cyclotetradecane (exoO2-cyclam) have been prepared of formula [M1{M2(exoO2-cyclam)}2][BPh4]2 where M1M2 = CoCo (3), ZnZn (4), MnCu (5), FeCu (6), CoCu (7), NiCu (8), ZnCu (9), and [(bipy)2Ru{Cu(exoO2-cyclam)}][NO3]2 (10). Complex 10 crystallised in the space group C2/c and shows Jahn–Teller distorted Cu(II) with axial nitrate ligands. The {Cu(exoO2-cyclam)} moiety chelates to the Ru with Ru–O distances of 2.082(5) Å. Complexes 5–10 show a Cu(II)/Cu(III) redox process and additional metal-centred (6, 8, 10) processes and ligand-centred (10) processes. The electrochemical and UV-Vis spectroelectrochemical study of 10 suggested two closely-spaced oxidations based on the Cu and Ru centres which suggests that substituted derivatives of 10 will be of interest for enhanced charge separation in dye-sensitised solar cells. Magnetic susceptibility measurements revealed dominant antiferromagnetic coupling within the trinuclear species 3, 5–8. Complex 10 showed Curie–Weiss behaviour with weak intermolecular interactions.
Co-reporter:Elaine A. M. Geary, Lesley J. Yellowlees, Simon Parsons, Luca Pilia, Angela Serpe, M. Laura Mercuri, Paola Deplano, Stewart J. Clark and Neil Robertson
Dalton Transactions 2007 (Issue 46) pp:5453-5459
Publication Date(Web):04 Oct 2007
DOI:10.1039/B712243H
[Ni(R2pipdt)(dmit)], (R2pipdt = 1,4-disubstituted-piperazine-3,2-dithione, R = CH2C6H5; dmit = 1,3-dithiole-2-thione-4,5-dithiolate) (1b) has been prepared and characterised and the properties compared with those of the known complex 2b belonging to the same class where R = Pri. Cyclic voltammetry of 1b and 2b was carried out and compared with that of the respective R2pipdt ligand precursors (1a and 2a). The nature of the R-groups of the pipdt ligand exerts an effect on the redox potentials and confirmed the position of the LUMO as mainly on the R2pipdt part of the complex. Accordingly the low frequency absorption, assigned to the HOMO–LUMO transition which has inter-ligand charge-transfer character, is found for 1b at lower frequency when compared to the corresponding transition of 2b. In situ EPR was carried out on electroreduced radical species of the R2pipdt ligand precursors (1a, 2a) and corresponding complexes (1b, 2b). This revealed considerable delocalisation of the unpaired electron on the R2pipdt ligand in 1b and 2b with coupling constants to N and H comparable with those of 1a and 2a. Complex 1b crystallised in the space group Pnma and shows an essentially planar complex (with out-of-plane R groups) π stacked at a distance of 3.65(1) Å. Such a one-dimensional structure is not achieved in the case of 2b, where the complex units are almost parallel and head-to-tail with each other forming dimers and this difference in solid-state packing is apparent in the diffuse reflectance spectrum of each. Plane-wave DFT calculations for 1b revealed a highly one-dimensional band structure with considerable band dispersion along the direction of greatest molecular interaction via
π-stacking.
Co-reporter:Dimitrios Maganas, Sarah S. Staniland, Alexios Grigoropoulos, Fraser White, Simon Parsons, Neil Robertson, Panayotis Kyritsis and Georgios Pneumatikakis
Dalton Transactions 2006 (Issue 19) pp:2301-2315
Publication Date(Web):14 Mar 2006
DOI:10.1039/B517938F
The S/Se-containing bidentate ligands LH of the type R2P(E)NHP(E)R′2, E = S, Se and R, R′ = Ph or iPr have been employed to synthesize ML2 (M = Mn, Co) complexes which contain the biologically important MS4 core. Theoretical calculations on the LH and L− forms of the ligands probe the geometric and electronic changes induced by the deprotonation of the LH form, which are correlated with structural data from X-ray crystallography. These results reflect the flexibility of the ligands, which enables them to be rather versatile with respect to the formation of ML2 complexes with varied geometries and MEPNPE metallacycle conformations. A series of old and new ML2 complexes have been synthesized and their structural, spectroscopic and magnetic properties characterized in detail. The nephelauxetic ratio β of the CoL2 complexes provides evidence of covalent interactions, whereas the EPR properties of the MnL2 complexes are interpreted on the basis of predominant ionic interactions, between the metal center and the ligands, respectively. Additional evidence for the existence of covalent interactions in the CoL2 complexes (R = Ph, iPr, or mixed Ph/iPr), is offered by comparisons between their 31P NMR. The aforementioned notations are supported by extensive theoretical calculations on the ML2 (E = S, R = Me) modelled structures, which probe the covalent and ionic character of the M–S bonds when M = Co or Mn. Wider implications of the findings of the present study on the M–S covalency and its importance in the active sites of various metalloenzymes are also discussed.
Co-reporter:Neil Robertson Dr.
Angewandte Chemie 2006 Volume 118(Issue 15) pp:
Publication Date(Web):9 MAR 2006
DOI:10.1002/ange.200503083
Farbstoffsensibilisierte Solarzellen (DSSCs) bieten sich als eine vielversprechende, billige Photovoltaiktechnologie an. Ihre Funktionsweise beruht auf der Ladungstrennung in einem Farbstoff, der sich an der Grenzfläche zwischen einem anorganischen Halbleiter und einem Lochleiter befindet. Durch sorgfältigen Entwurf der Farbstoffkomponente lassen sich Energieverlustmechanismen minimieren und Lichtsammelausbeuten erhöhen. Probleme, die gegenwärtig den Masseneinsatz von DSSCs verhindern, sind die umständliche Fertigung der Bauelemente und die mangelnde Langzeitstabilität des flüssigen Redoxelektrolyten, der in den bislang wirksamsten Zellen eingesetzt wird. In diesem Kurzaufsatz untersuchen wir Strategien zur Entwicklung von Farbstoffen, die in neuartigen Zellentwürfen mit alternativen Flüssigelektrolyten eingesetzt werden können. Solche Feststoff- und Gel-DSSCs sind vielversprechende Elemente für billige, effiziente und robuste Photovoltaiksysteme.
Co-reporter:Neil Robertson
Angewandte Chemie International Edition 2006 45(15) pp:2338-2345
Publication Date(Web):
DOI:10.1002/anie.200503083
Co-reporter:Sarah S. Staniland, Wataru Fujita, Yoshikatsu Umezono, Kunio Awaga, Stewart J. Clark, HengBo Cui, Hayao Kobayashi and Neil Robertson
Chemical Communications 2005 (Issue 25) pp:3204-3206
Publication Date(Web):24 May 2005
DOI:10.1039/B502783G
A new molecular conducting material, [BDTA][Ni(dmit)2]2, with a novel multiband electronic structure has been prepared by simple mixing of precursor salts of the components.
Co-reporter:Vivienne A. White, Nicholas J. Long and Neil Robertson
Organic & Biomolecular Chemistry 2005 vol. 3(Issue 23) pp:4268-4273
Publication Date(Web):02 Nov 2005
DOI:10.1039/B510734B
A series of new N4 and N8 macrocycles has been prepared, that includes cis-exogenous O2, S2 and S/O atoms to allow chelation to a metal external to the macrocyclic ring. We found that thioamide units within the macrocycles were unstable to attack by secondary amines and thus alkylated precursors containing only tertiary amines could lead to exogenous-S2 macrocycles. Cyclisation of alkylated tetraamine precursors with dimethyloxalate or dithiooxamide led to both N4 and N8 macrocycles via 1 + 1 and 2 + 2 cyclisation reactions with exogenous-O2 or S2 respectively. Alkylation of preformed exogenous-O2 macrocycles was explored and led to alkyl substitution at the secondary amine nitrogens in the ring, however synthesis of these species was overall lower yielding than cyclisation using alkylated tetraamine precursors. Thionation of an exo-O2 macrocycle using an analogue of Lawesson's Reagent led to formation of the analogous exogenous-S2 and exogenous-O,S macrocycles. Related S2N2 macrocycles with exogenous-O2 were prepared by a cyclisation route but could not be isolated free of larger ring analogues.
Co-reporter:Hilary J. Hartigan, Georg Seeber, Andrew R. Mount, Lesley J. Yellowlees and Neil Robertson
New Journal of Chemistry 2004 vol. 28(Issue 1) pp:98-103
Publication Date(Web):31 Oct 2003
DOI:10.1039/B309317D
Two new redox-active macrocycles 2 and 3 have been prepared based on an 18-membered S4N2–donor ring conjugated to one or two CpCo(dithiolene) redox/chromophore units respectively. Cyclic voltammetry for 2 showed one reversible reduction process at −0.29 V and EPR spectroscopy of the reduced form indicated a significant degree of delocalisation of the unpaired electron. The compound 2 showed an intense low-energy absorption at 675 nm (in CH2Cl2) that was shown to shift to higher energy during electrochemical reduction. Interaction of 2 with guest Ag(I) ions was followed by monitoring changes in the electrochemical and spectroscopic behaviour with sequential additions of the guest metal ion and by electrochemistry at a silver electrode. UV/Vis spectroscopic results indicated a strong interaction of Ag(I) with 2 involving large changes in the electronic nature of the macrocycle chromophore. Cyclic voltammetry also indicated interaction between 2 and Ag(I) and suggested the involvement of a film containing 2 on the electrode surface.
Co-reporter:Elaine A. M. Geary, Narukuni Hirata, John Clifford, James R. Durrant, Simon Parsons, Alice Dawson, Lesley J. Yellowlees and Neil Robertson
Dalton Transactions 2003 (Issue 19) pp:3757-3762
Publication Date(Web):2003/08/27
DOI:10.1039/B306241D
The platinum diimine dithiolate complex, [Pt(2,2′-bipyridyl-5,5′-dicarboxylicacid)(3,4-toluenedithiolate)]
([Pt(5,5′-dcbpy)(tdt)]) and its tetrabutylammonium salt [TBA]2[Pt(5,5′-dcbpy)(tdt)] have been prepared, spectroscopically and electrochemically characterised and attached on to TiO2 substrate to be used as solar cell sensitisers. A single-crystal X-ray structure was obtained for [TBA]2[Pt(5,5′-dcbpy)(tdt)]·EtOH·EtOAc. The effect of the position of the two carboxylic acid substituents on the electrochemistry of the 5,5′-disubstituted complexes is discussed in comparison with the previously reported [Pt(4,4′-dcbpy)(tdt)]. Electrochemical studies show no major change in the HOMO after movement of the carboxylic acid groups, consistent with assignment of the HOMO as largely dithiolate based. Movement of the carboxylic acid groups makes the diimine electronic character and hence the LUMO of the complexes different. Electrochemical studies show a change to lower energy of the LUMO represented by changes in reduction potential of the compound on moving the carboxylic acid substituents from the 4,4′ to the 5,5′ positions. Both [Pt(5,5′-dcbpy)(tdt)] and [TBA]2[Pt(5,5′-dcbpy)(tdt)] have been used as solar cell sensitisers, with the di-TBA salt giving lower dye loading but superior photovoltaic performance. The consequences of tuning the complex through the position of the carboxylic acid groups are discussed.
Co-reporter:Neil Robertson, Leroy Cronin
Coordination Chemistry Reviews 2002 Volume 227(Issue 1) pp:93-127
Publication Date(Web):April 2002
DOI:10.1016/S0010-8545(01)00457-X
Crystalline materials studied for their conducting or magnetic properties based on metal complexes of 1,2-dithiolene ligands are discussed emphasising the wide diversity of ligands now available and the variety of materials prepared from these. Complexes have been prepared using electronically delocalised dithiolene ligands where the core complex is extended with units such as thioethers, aromatics, tetrathiafulvalene (TTF) and other heterocycles to explore the influence of these variations on the solid-state structures and properties derived from them. Although superconductivity in dithiolene complexes has so far been limited to [M(dmit)2]X− salts, other ligand systems have given rise to numerous conducting and metallic salts and have proven informative in rationalising the criteria for design of the molecular units. Novel material properties have been observed in systems such as hybrid conducting ∣ magnetic materials and mixed dithiolene-metallocene salts. In particular, highly conducting and metallic single-component materials have recently been found uniquely within materials based on metal-bis-1,2-dithiolene complexes. Magnetic materials containing dithiolene-complex building blocks have yielded systems such as ferromagnets, ferrimagnets, metamagnets and spin ladders in addition to other model systems suitable for the study of magnetic ordering. These can involve systems where the dithiolene complex is the only paramagnetic component in addition to more complex systems involving other types of building block.
Co-reporter:Leroy Cronin, Stewart J. Clark, Simon Parsons, Takayoshi Nakamura and Neil Robertson
Dalton Transactions 2001 (Issue 8) pp:1347-1351
Publication Date(Web):20 Mar 2001
DOI:10.1039/B008299F
Preparation by electrocrystallisation has been carried out for the salts [Rb(anti-dchyl-18c6)]2[Ni(dmit)2] 1, [Rb(anti-dchyl-18c6)][Ni(dmit)2] 2, [Cs(anti-dchyl-18c6)]2[Ni(dmit)2] 3 and [Cs(anti-dchyl-18c6)1.5][Ni(dmit)2]64 (anti-dchyl-18c6 = cis-anti-cis-dicyclohexyl-18-crown-6, dmit = C3S5). Salts 1 and 3 involve the planar dianionic nickel complex sandwiched by two metal–crown units. This leads to short Rb+⋯Ni and Rb+⋯S interactions in 1 and the shortest recorded Cs+⋯Ni distance of 3.47 Å in 3, presumably stabilised by the four surrounding S atoms at 3.73–4.44 Å. DFT calculations on the dianionic salts 1 and 3 indicate an essentially electrostatic interaction between the [Ni(dmit)2]2− complex and the Rb+ or Cs+ ion and show frontier orbitals qualitatively similar to those previously derived from EHMO calculations on molecular conductors containing [Ni(dmit)2]. Salt 2 consists of non-stacked nickel complexes arranged in chains linked by S⋯Rb+ interactions through the terminal sulfurs with the Rb+ ion placed exactly within the plane of the crown oxygens. Magnetic susceptibility measurement indicated weak antiferromagnetic interactions. Salt 4 shows a 2-D sheet of nickel complexes stacked in a herringbone arrangement separated by layers of counter ions complexed by the crowns in a disordered manner with the anion ∶ cation ratio of 6 ∶ 1 uniquely high among [Ni(dmit)2]x− salts. Salt 4 displays semiconductor behaviour with σRT = 10−2 S cm−1.
Co-reporter:N. Robertson;K. Awaga;S. Parsons;A. Kobayashi;A. E. Underhill
Advanced Functional Materials 1998 Volume 8(Issue 2) pp:
Publication Date(Web):4 DEC 1998
DOI:10.1002/(SICI)1099-0712(199803/04)8:2<93::AID-AMO335>3.0.CO;2-B
The salt [TTF]2[Fe(tdas)2] has been prepared by electocrystallisation and its conductivity and magnetic properties are reported. The X-ray structure has been determined. © 1998 John Wiley & Sons, Ltd.
Co-reporter:Charlotte L. Linfoot, Patricia Richardson, Keri L. McCall, James R. Durrant, Ana Morandeira, Neil Robertson
Solar Energy (June 2011) Volume 85(Issue 6) pp:1195-1203
Publication Date(Web):1 June 2011
DOI:10.1016/j.solener.2011.02.023
We report the first example of a Ni(II) complex that demonstrates sensitiser function in a Dye-Sensitised Solar Cell (DSSC). Complexes [Ni(dcbpy)(qdt)] (1), [Ni(decbpy)(qdt)] (2) and [Ni(decbpy)Cl2] (3) (where dcbpy = 4,4′-dicarboxy-2,2′-bipyridine; decbpy = 4,4′-di(CO2Et)-2,2′-bipyridine; and qdt = quinoxaline-2,3-dithiolate) have been prepared. Characterisation was carried out using electrochemical, spectroscopic and computational techniques. Intensive visible transitions of 1 and 2 have been assigned predominantly to Ligand-to-Ligand Charge Transfer (LLCT) from the qdt to the diimine ligand, suggesting appropriate charge separation for application in a photoelectrochemical device. TiO2 sensitised with 2, following charge injection, processes a recombination time significantly long for photovoltaic function. In a DSSC, using I-/I3- redox electrolyte, photocurrents and photovoltages of 0.293 mA and 521 mV were observed, with optimum values requiring TiCl4 post-treatment of TiO2 and co-adsorption of Chenodeoxycholic acid (Cheno). Although photovoltaic function was observed, the low photocurrent is attributed to a short-lived excited state lifetime resulting in poor charge injection from the Ni(II) sensitiser.
Co-reporter:Ekaterina A. Knyazeva, Wenjun Wu, Timofey N. Chmovzh, Neil Robertson, J. Derek Woollins, Oleg A. Rakitin
Solar Energy (1 March 2017) Volume 144() pp:134-143
Publication Date(Web):1 March 2017
DOI:10.1016/j.solener.2017.01.016
Co-reporter:Sushobhan Ghosh, Georg T. Silber, Andrew J. P. White, Neil Robertson and Ramon Vilar
Dalton Transactions 2013 - vol. 42(Issue 38) pp:NaN13816-13816
Publication Date(Web):2013/08/12
DOI:10.1039/C3DT51845K
The synthesis of a terpyridine–guanosine ligand and its reaction with copper(II) to yield a new [2 + 2] metallo-rectangle is reported. The metallo-rectangle was characterized by single crystal X-ray diffraction and the structure showed significant intramolecular π–π stacking interactions between the two terpyridine moieties of the molecule. This prompted us to investigate the magnetic properties of the new di-copper(II) assembly which displayed ferromagnetic interactions in the solid state.
Co-reporter:Elaine A. M. Geary, Lesley J. Yellowlees, Simon Parsons, Luca Pilia, Angela Serpe, M. Laura Mercuri, Paola Deplano, Stewart J. Clark and Neil Robertson
Dalton Transactions 2007(Issue 46) pp:NaN5459-5459
Publication Date(Web):2007/10/04
DOI:10.1039/B712243H
[Ni(R2pipdt)(dmit)], (R2pipdt = 1,4-disubstituted-piperazine-3,2-dithione, R = CH2C6H5; dmit = 1,3-dithiole-2-thione-4,5-dithiolate) (1b) has been prepared and characterised and the properties compared with those of the known complex 2b belonging to the same class where R = Pri. Cyclic voltammetry of 1b and 2b was carried out and compared with that of the respective R2pipdt ligand precursors (1a and 2a). The nature of the R-groups of the pipdt ligand exerts an effect on the redox potentials and confirmed the position of the LUMO as mainly on the R2pipdt part of the complex. Accordingly the low frequency absorption, assigned to the HOMO–LUMO transition which has inter-ligand charge-transfer character, is found for 1b at lower frequency when compared to the corresponding transition of 2b. In situ EPR was carried out on electroreduced radical species of the R2pipdt ligand precursors (1a, 2a) and corresponding complexes (1b, 2b). This revealed considerable delocalisation of the unpaired electron on the R2pipdt ligand in 1b and 2b with coupling constants to N and H comparable with those of 1a and 2a. Complex 1b crystallised in the space group Pnma and shows an essentially planar complex (with out-of-plane R groups) π stacked at a distance of 3.65(1) Å. Such a one-dimensional structure is not achieved in the case of 2b, where the complex units are almost parallel and head-to-tail with each other forming dimers and this difference in solid-state packing is apparent in the diffuse reflectance spectrum of each. Plane-wave DFT calculations for 1b revealed a highly one-dimensional band structure with considerable band dispersion along the direction of greatest molecular interaction via
π-stacking.
Co-reporter:Vivienne A. White, Russell D. L. Johnstone, Keri L. McCall, Nicholas J. Long, Alexandra M. Z. Slawin and Neil Robertson
Dalton Transactions 2007(Issue 27) pp:NaN2948-2948
Publication Date(Web):2007/05/10
DOI:10.1039/B701166K
Complexes of the ligand 2,3-dioxo-1,4,8,11-tetraaza-cyclotetradecane (exoO2-cyclam) have been prepared of formula [M1{M2(exoO2-cyclam)}2][BPh4]2 where M1M2 = CoCo (3), ZnZn (4), MnCu (5), FeCu (6), CoCu (7), NiCu (8), ZnCu (9), and [(bipy)2Ru{Cu(exoO2-cyclam)}][NO3]2 (10). Complex 10 crystallised in the space group C2/c and shows Jahn–Teller distorted Cu(II) with axial nitrate ligands. The {Cu(exoO2-cyclam)} moiety chelates to the Ru with Ru–O distances of 2.082(5) Å. Complexes 5–10 show a Cu(II)/Cu(III) redox process and additional metal-centred (6, 8, 10) processes and ligand-centred (10) processes. The electrochemical and UV-Vis spectroelectrochemical study of 10 suggested two closely-spaced oxidations based on the Cu and Ru centres which suggests that substituted derivatives of 10 will be of interest for enhanced charge separation in dye-sensitised solar cells. Magnetic susceptibility measurements revealed dominant antiferromagnetic coupling within the trinuclear species 3, 5–8. Complex 10 showed Curie–Weiss behaviour with weak intermolecular interactions.
Co-reporter:Lucy P. Moorcraft, Ana Morandeira, James R. Durrant, James R. Jennings, Laurence M. Peter, Simon Parsons, Andrew Turner, Lesley J. Yellowlees and Neil Robertson
Dalton Transactions 2008(Issue 48) pp:NaN6947-6947
Publication Date(Web):2008/11/03
DOI:10.1039/B811943K
The dye complexes [Pt(4-CO2R-py)2(mnt)] (R = H (3a), CH3 (3b)) and the precursor complexes [Pt(4-CO2R-py)2Cl2] (2a, 2b) (py = pyridyl) were synthesised, characterised by electrochemical, spectroscopic, spectroelectrochemical (UV-vis-nIR and in situEPR) and hybrid DFT computational methods and attached to a TiO2 substrate to determine charge recombination kinetics. The results were compared to the bipyridyl analogues [Pt{X,X′-(CO2R)-2,2′-bipyridyl}(mnt)], (X = 3 or 4). The electronic characteristics of the bis-pyridyl complex were found to be different to the bipyridyl complexes making the former harder to reduce, shifting the lowest-energy absorption band to higher energy and showing separate degenerate LUMO orbitals on the two pyridine rings. The latter point determines that the di-reduced pyridyl complex remains EPR active, unlike the bipyridyl analogue. Complex 3a attached to nanocrystalline TiO2 shows a long charge recombination lifetime in comparison with the analogous complex with the ubiquitous 4,4′-(CO2H)2-bipyridyl ligand, suggesting that pyridyl complexes may possess some advantage over bipyridyl complexes in dye-sensitised solar cells.
Co-reporter:Elaine A. M. Geary, Keri L. McCall, Andrew Turner, Paul R. Murray, Eric J. L. McInnes, Lorna A. Jack, Lesley J. Yellowlees and Neil Robertson
Dalton Transactions 2008(Issue 28) pp:NaN3708-3708
Publication Date(Web):2008/05/29
DOI:10.1039/B719789F
A series of [Pt(II)(diimine)(dithiolate)] complexes of general formula [Pt{X,X′-(CO2R)2-bpy}(mnt)] (where X = 3, 4 or 5; R = H or Et, bpy = 2,2′-bipyridyl and mnt = maleonitriledithiolate), have been spectroscopically, electrochemically and computationally characterised and compared with the precursors [Pt{X,X′-(CO2R)2-bpy}Cl2] and X,X′-(CO2R)2-bpy. The study includes cyclic voltammetry, in situEPR spectroelectrochemical studies of fluid solution and frozen solution samples, UV/Vis/NIR spectroelectrochemistry, hyrid DFT and TD-DFT calculations. The effect of changing the position of the bpy substituents from 3,3′ to 4,4′ and 5,5′ is discussed with reference to electronic changes seen within the different members of the family of molecules. The performance of the mnt complexes in dye-sensitised solar cells has been previously described and the superior performance of [Pt{3,3′-(CO2R)2-bpy}(mnt)] is now explained in terms of decreased electronic delocalisation through twisting of the bipyridyl ligand as supported by the EPR and computational results.
Co-reporter:Simon Dalgleish, Carole A. Morrison, Derek S. Middlemiss, Andrew R. Mount, Anna Collins, Luca Pilia, Angela Serpe, M. Laura Mercuri, Susan J. Roberts-Bleming, Adam Charlton, Paola Deplano, Patrick J. Murphy and Neil Robertson
Journal of Materials Chemistry A 2009 - vol. 19(Issue 34) pp:NaN6200-6200
Publication Date(Web):2009/07/08
DOI:10.1039/B907028A
The synthesis, structure and spectroscopic properties of a new class of asymmetric nickel dithiolene complex containing pendent thiophene units [Ni(R2pipdt)(b-3ted)] are described {R = Bz (3), iPr (4); pipdt = piperazine-3,2-dithione; b-3ted = bis(3-thienyl)-1,2-ethylenedithiolene}. X-ray crystallography of both neutral species shows planar nickel dithiolene units and the thiophene groups twisted out of the molecular plane, with the R group having a large effect on the packing structure. DFT geometry calculations show good agreement with experimental data for 3 and 4 and confirm that the low energy absorption, assigned to a HOMO → LUMO transition, is inter-ligand charge-transfer in character. Solid state calculations show greater band dispersion in 4, which corresponds to a closer packing in the crystal lattice. Cyclic voltammetry of both complexes displays three reversible processes, corresponding to an interconversion between cationic, neutral, anionic and dianionic species, with tuning of the redox potentials by variation of the R group. Electrochemical polymerisation of 3 shows incorporation of intact dithiolene units into a polymer film with redox functionality similar to that of the monomer, whereas co-polymerisation of 3 with thiophene yields a highly conductive film with redox functionality similar to polythiophene and enhanced absorption across the near IR.
Co-reporter:Miquel Planells, Luke X. Reynolds, Umesh Bansode, Shraddha Chhatre, Satishchandra Ogale, Neil Robertson and Saif A. Haque
Physical Chemistry Chemical Physics 2013 - vol. 15(Issue 20) pp:NaN7684-7684
Publication Date(Web):2013/04/17
DOI:10.1039/C3CP50980J
We report the synthesis and optical characterisation of different triphenylamine-based hole capture materials able to anchor to CdSe quantum dots (QDs). Cyclic voltammetry studies indicate that these materials exhibit reversible electrochemical behaviour. Photoluminescence and transient absorption spectroscopy techniques are used to study interfacial charge transfer properties of the triphenylamine functionalized CdSe QDs. Specifically, we show that the functionalized QDs based on the most easily oxidised triphenylamine display efficient hole-extraction and long-lived charge separation. The present findings should help identify new strategies to control charge transfer QD-based optoelectronic devices.
Co-reporter:Maxwell Reinhardt, Simon Dalgleish, Yoshiaki Shuku, Louisa Reissig, Michio M. Matsushita, Jason Crain, Kunio Awaga and Neil Robertson
Physical Chemistry Chemical Physics 2017 - vol. 19(Issue 9) pp:NaN6776-6776
Publication Date(Web):2017/02/10
DOI:10.1039/C6CP08685C
The structure and electronic properties of a novel cobalt half sandwich complex of cyclopentadiene (Cp) and diaminonaphthalene (DAnap) [CpCo(DAnap)] are described and compared to the previously reported diaminobenzene derivative [CpCo(DAbnz)] in view of their potential for (opto)electronic device application. Both complexes show stable redox processes, tunable through the diaminoacene ligand, and show strong absorption in the visible region, with additional transitions stretching into the near infrared (NIR). CpCo(DAnap) crystallises with a particularly large unit cell (9301 Å3), comprising 32 molecules, with a gradual rotation over 8 molecules along the long c-axis. In the solid state the balance of the optical transitions in both complexes is reversed, with a suppression of the visible band and an enhancement of the NIR band, attributed to extensive intermolecular electronic interaction. In the case of CpCo(DAnap), highly crystalline thin films could be formed under physical vapor deposition, which show a photocurrent response stretching into the NIR, and p-type semiconductor behavior in field effect transistors with mobility values of the order 1 × 10−4 cm2 V−1 s−1. The device performance is understood through investigation of the morphology of the grown films.
Co-reporter:Tania Anjos, Susan J. Roberts-Bleming, Adam Charlton, Neil Robertson, Andrew R. Mount, Simon J. Coles, Michael B. Hursthouse, Maher Kalaji and Patrick J. Murphy
Journal of Materials Chemistry A 2008 - vol. 18(Issue 4) pp:NaN483-483
Publication Date(Web):2007/12/07
DOI:10.1039/B714372A
The synthesis, electrochemical and spectroscopic properties of the new thiophene-substituted metal dithiolene complexes [Ni(b-3ted)2] (3) and [NBu4][Ni(b-3ted)2] ([NBu4][3]) are described [b-3ted = bis(3-thienyl)-1,2-ethylenedithiolene] and compared with new studies of the known compounds [Ni(b-2ted)2] (2) and [NBu4][Ni(b-2ted)2] ([NBu4][2]). X-Ray structures were determined for the neutral complexes 2 and 3 and both showed planar nickel dithiolene units with thiophene groups twisted out of the molecular plane, precluding close molecular π-stacking. Electrochemical investigations revealed two redox processes corresponding to interconversion between neutral, monoanionic and dianionic species for 3, analogous to 2. Oxidation of 0.1 mM [3]− in CH3CN was shown to give a green molecular film of 3 which, in contrast to as-prepared crystals of 3, showed significant conductivity. Electrochemical polymerisation of 3 carried out at different concentrations resulted in films; electrochemical, SNIFTIRS and UV-Vis results were consistent with incorporation of the intact metal dithiolene complex in these films. In contrast, electrochemical polymerisation of 2 gave a film charateristic of a polymerised thiophene but with no evidence of incorporation of the intact metal dithiolene complex. Copolymerisation of 3 with thiophene gave a gold-coloured electropolymerised film of significant conductivity that, upon dissolution in CH2Cl2, showed the characteristic low energy absorption of the Ni-dithiolene complex, confirming its incorporation. This copolymerisation approach offers a versatile route to the synthesis of metal dithiolene–polythiophene hybrid films.
Co-reporter:Kuan-Lin Wu, Yue Hu, Chun-Tien Chao, Ya-Wen Yang, Ting-Yun Hsiao, Neil Robertson and Yun Chi
Journal of Materials Chemistry A 2014 - vol. 2(Issue 45) pp:NaN19565-19565
Publication Date(Web):2014/10/07
DOI:10.1039/C4TA04208E
Three isomeric Ru(II) metal complexes with distinctively oriented tpiq ancillary chelates, TFRS-80a, 80b and 80c, were prepared from the condensation of Ru(4,4′-diethoxycarbonyl-2,2′-bipyridine) (p-cymene)Cl with tpiqH, i.e. 6-(5-(2,6-bis(hexyloxy)phenyl)thiophen-2-yl)-1-(3-(trifluoromethyl)-1H-pyrazol-5-yl)isoquinoline. Photophysical and electrochemical investigations, together with DFT and TD-DFT calculations, allowed a comprehensive understanding of their basic properties in both solution state and on TiO2 surface. DSC cells with both an ultra-thin layer of transparent TiO2 (3.6 μm) and I−/I3− electrolyte were fabricated, for which the symmetric sensitizers TFRS-80a and 80c showed better performances (η = 8.37 and 8.26%) over that of the asymmetric counterpart TFRS-80b (η = 5.55%), the latter suffered from poor dye loading and consequently lowered JSC and VOC. In sharp contrast, all DSC cells with [Co(phen)3]2+/3+ electrolyte gave superior efficiencies (η = 8.36–9.06%), for which the thiocyanate-free architecture, the improved light harvesting capability, and the possession of conjugated and bulky 5-(2,6-bis(hexyloxy)phenyl)thiophen-2-yl functional moieties are three primary factors governing the observed results.
Co-reporter:Che-Wei Hsu, Yongbiao Zhao, Hsiu-Hsuan Yeh, Chin-Wei Lu, Cong Fan, Yue Hu, Neil Robertson, Gene-Hsiang Lee, Xiao Wei Sun and Yun Chi
Journal of Materials Chemistry A 2015 - vol. 3(Issue 41) pp:NaN10847-10847
Publication Date(Web):2015/09/16
DOI:10.1039/C5TC02261D
Potential dianionic chelates, 5,5′-bis(trifluoromethyl)-2H,2′H-3,3′-bipyrazole (bipzH2) and 5,5′-(1-methylethylidene)-bis(3-trifluoromethyl-1H-pyrazole) (mepzH2), were synthesized from Claisen condensation employing ethyl trifluoroacetate with 2,3-butanedione and with 3,3-dimethyl-2,4-pentanedione, followed by hydrazine cyclization. These chelates were then utilized in the preparation of four emissive Pt(II) metal complexes [Pt(tbbpy)(bipz)] (1), [Pt(msbpy)(bipz)] (2), [Pt(tbbpy)(mepz)] (3) and [Pt(msbpy)(mepz)] (4), where tbbpy and msbpy represent 4,4′-di-t-butyl-2,2′-bipyridine and 4,4′-dimesityl-2,2′-bipyridine, respectively. Single crystal X-ray structural analyses of 2 and 3 were executed to unveil the basic coordination geometry around the Pt(II) center as well as the π–π stacking interaction in the solid state. These complexes are essentially non-emissive in solution (Q. Y. = 0.2–0.4%), but are highly luminescent in the solid state with QY of 52% and 83% and τobs of 368 ns and 8.37 μs for 1 and 3, respectively. Their photophysical properties were measured and discussed on the basis of computational approaches. For applications, non-doped organic light emitting diodes (OLEDs) were fabricated using 1 and 3 as emitters, exhibiting red-orange emission with a maximum luminance of 43000 cd m−2, an EQE of 19.0%, a CE of 21.0 cd A−1 and a PE of 15.5 lm W−1, and yellow emission with a maximum luminance of 5100 cd m−2, an EQE of 7.1%, a CE of 21.0 cd A−1 and a PE of 11.3 lm W−1, respectively. The particularly higher OLED efficiencies of 1versus3 highlight the design principle of Pt(II) based phosphors, particularly for the fabrication of a non-doped OLED architecture.
Co-reporter:Omar Moudam, Brenda C. Rowan, Mohammed Alamiry, Patricia Richardson, Bryce S. Richards, Anita C. Jones and Neil Robertson
Chemical Communications 2009(Issue 43) pp:NaN6651-6651
Publication Date(Web):2009/09/25
DOI:10.1039/B914978C
We have prepared complexes of formula [Eu(β-diketonate)3(DPEPO)] and shown quantitative excited-state energy transfer from the ligands combined with efficient Ln luminescence leading to exceptionally-high total photoluminescence quantum yield of up to 80% in solution and in PMMA.
Co-reporter:Simon Dalgleish and Neil Robertson
Chemical Communications 2009(Issue 39) pp:NaN5828-5828
Publication Date(Web):2009/09/09
DOI:10.1039/B913174D
A novel nickel dithiolene-containing polymer, generated by the electropolymerisation of pendent indole units, has been prepared and shows good stability and fast reversible switching of the near infrared absorption by varying the applied potential of the film.
Co-reporter:Simon Dalgleish, Kunio Awaga and Neil Robertson
Chemical Communications 2011 - vol. 47(Issue 25) pp:NaN7091-7091
Publication Date(Web):2011/05/27
DOI:10.1039/C1CC12344K
Thin films of neutral copper dithiolenes have been prepared by potentiostatic electrodeposition. This method allows the isolation of near infrared (NIR) active species, in a useable form, that are otherwise unobtainable by conventional chemical methods.
Co-reporter:Simon Dalgleish, Hirofumi Yoshikawa, Michio M. Matsushita, Kunio Awaga and Neil Robertson
Chemical Science (2010-Present) 2011 - vol. 2(Issue 2) pp:NaN320-320
Publication Date(Web):2010/10/29
DOI:10.1039/C0SC00446D
Electrooxidation to form neutral films of a homoleptic nickel dithiolene [Ni(b-3ted)2] (1) from an air-stable TBA salt is described [b-3ted = bis(3-thienyl)-1,2-ethylenedithiolene; TBA = tetrabutylammonium]. Films grown by potentiostatic electrodeposition directly onto interdigitated electrode arrays show improved conductivity compared to those formed by solution methods. The grown films are free from residual electrolyte doping, and this technique is shown to yield robust films of reproducible electronic performance. The conductivity of films formed by electrodeposition show gate dependence when grown directly onto field effect transistor substrates. Thin-film X-ray diffraction confirms the electrodeposited films to be of the same polymorph as films and single crystals formed by solution methods. Scanning electron microscopy shows the electrodeposited films to have larger, more connected polycrystalline regions, as well as improved contact with the electrodes.
Co-reporter:Miquel Planells, Antonio Abate, Derek J. Hollman, Samuel D. Stranks, Vishal Bharti, Jitender Gaur, Dibyajyoti Mohanty, Suresh Chand, Henry J. Snaith and Neil Robertson
Journal of Materials Chemistry A 2013 - vol. 1(Issue 23) pp:NaN6960-6960
Publication Date(Web):2013/05/01
DOI:10.1039/C3TA11417A
We have synthesized and characterized a series of triphenylamine-based hole-transport materials (HTMs), and studied their function in solid-state dye sensitized solar cells (ss-DSSCs). By increasing the electron-donating strength of functional groups (–H < –Me < –SMe < –OMe) we have systematically shifted the oxidation potential and ensuing photocurrent generation and open-circuit voltage of the solar cells. Correlating the electronic properties of the HTM to the device operation highlights a significant energy offset required between the Dye – HTM highest occupied molecular orbital (HOMO) energy levels. From this study, it is apparent that precise control and tuning of the oxidation potential is a necessity, and usually not achieved with most HTMs developed to date for ss-DSSCs. To significantly increase the efficiency of solid-state DSSCs understanding these properties, and implementing dye-HTM combinations to minimize the required HOMO offset is of central importance.
Co-reporter:Xing Li, Yue Hu, Irene Sanchez-Molina, Ying Zhou, Fengtao Yu, Saif A. Haque, Wenjun Wu, Jianli Hua, He Tian and Neil Robertson
Journal of Materials Chemistry A 2015 - vol. 3(Issue 43) pp:NaN21743-21743
Publication Date(Web):2015/09/21
DOI:10.1039/C5TA07254A
Three new quinoxaline-based organic dyes (AQ201, AQ202, and AQ203), containing thiophene, 3,4-ethylenedioxythiophene (EDOT), and cyclopentadithiophene (CPDT) in the π-system, respectively, have been designed and synthesized for dye-sensitized solar cells. Different from the traditional donor–π-bridge–acceptor (D–π–A) type dyes, the dissymmetric π-bridge on both sides of quinoxaline enables great flexibility in fine-tuning the absorption spectra and energy levels of the resultant molecules. By changing the π-bridge between the bulky triphenylamine donor and quinoxaline group, a negative shift was observed regarding the highest occupied molecular orbital (HOMO) levels of AQ201, AQ202, and AQ203 dyes (0.88, 0.79, and 0.72 V vs. NHE, respectively), while the lowest unoccupied molecular orbital (LUMO) levels of these dyes remained the same (−1.19, −1.20, and −1.20 V vs. NHE, respectively), which, in turn, resulted in a gradual shift of the absorption spectra of AQ dyes. The absorption spectra properties of the dyes are also analysed by density functional theory. The calculated results in combination with the experiments indicate that the absorption bands are mainly dominated by charge transfer transitions from the HOMO and HOMO−1 orbital to the LUMO. In all cases, the [Co(bpy)3]2+/3+ redox-shuttle afforded superior solar cell performance compared to I−/I3−. More importantly, dye AQ202 shows the highest power conversion efficiency (PCE) of 8.37% with the [Co(bpy)3]2+/3+ based electrolyte by maintaining a balance between the spectral absorption range and driving force for dye regeneration. Transient photocurrent decay experiments as well as electrochemical impedance spectroscopy indicate that the lower HOMO levels lead to higher electron lifetime and dye regeneration efficiency.
Co-reporter:Keri L. McCall, Ana Morandeira, James Durrant, Lesley J. Yellowlees and Neil Robertson
Dalton Transactions 2010 - vol. 39(Issue 17) pp:NaN4145-4145
Publication Date(Web):2010/03/18
DOI:10.1039/B924660F
The control of the loss mechanism in a dye sensitised solar cell (DSSC) via recombination of the injected electron with the oxidised dye was investigated by incorporating a redox-active ligand, 6,7-bis(methylthio)tetrathiafulvalene dithiolate (TTF(SMe)2), into a ruthenium bipyridyl dye. A series of dyes with general formula [Ru(4,4′-R-bpy)2(TTF(SMe)2], where R = H, CO2Et and CO2H, were synthesised and characterised using electrochemistry, absorption and emission spectroscopy, spectroelectrochemistry and hybrid-DFT calculations. In addition, the performance of the acid derivative in a DSSC was investigated using IV measurements, as well as transient absorption spectroscopy. These complexes showed significant TTF-ligand character to the HOMO orbital, as deduced by spectroelectrochemical, emission and computational studies. Upon adsorption of the acid derivative to TiO2 a long-lived charge-separated state of 20 ms was observed via transient absorption spectroscopy. Despite this long-lived charge-separated state, the dye yielded extremely low DSSC efficiencies, attributed to the poor regeneration of the neutral dye by iodide. As a result, the complex forms a novel long-lived charge separated state that persists even under working solar cell electrolyte conditions.
Co-reporter:Michal Maciejczyk, Aruna Ivaturi and Neil Robertson
Journal of Materials Chemistry A 2016 - vol. 4(Issue 13) pp:NaN4863-4863
Publication Date(Web):2016/03/02
DOI:10.1039/C6TA00110F
Four spiro[fluorene-9,9′-xanthene] (SFX) derivatives, SFX-TAD, SFX-TCz, SFX-TPTZ and SFX-MeOTAD have been synthesized for use as hole-transport materials and fully characterized by 1H/13C NMR spectroscopy, mass spectrometry, XRD and DSC. Their thermal, optical and electrochemical properties were investigated. The use of different substituents affects the highest occupied molecular orbital (HOMO) energy level proving the versatility of the central core towards the facile and low-cost preparation of spiro-hole-transport materials. Among the synthesized SFX derivatives, SFX-MeOTAD was employed as hole-transporting material (HTM) and the performance tested in perovskite solar cells with device architecture glass/FTO/compact TiO2/mesoporous Al2O3/CH3NH3PbI3−xClx/HTM/Au. SFX-MeOTAD gave a comparable efficiency to spiro-MeOTAD, demonstrating great potential for use of the SFX family as cost effective and versatile hole conductors facilitating commercialization of perovskite solar cells (PSCs).
Co-reporter:Emily Allwright, Dominik M. Berg, Rabie Djemour, Marc Steichen, Phillip J. Dale and Neil Robertson
Journal of Materials Chemistry A 2014 - vol. 2(Issue 35) pp:NaN7238-7238
Publication Date(Web):2014/07/30
DOI:10.1039/C4TC01134A
Electrochemical deposition is shown to be a novel technique to deposit films of N,N′-dibutylperylene-3,4:9,10-bis(dicarboximide) (BuPTCDI) dye that avoids the need for high vacuum or solubilising side chains on the molecule. The technique exploits the higher solubility of the reduced ionic form of the dye over the neutral form. BuPTCDI was chemically reduced to solubilise and then electrochemically oxidised to form a film on various substrates. The properties of the films were investigated by UV/Vis spectroscopy, Photoluminescence, Raman spectroscopy, X-ray diffraction, SEM and photoconductivity showing the successful deposition of the BuPTCDI molecules. The technique was also used to deposit films on interdigitated-electrode substrates enabling measurement of field-effect mobility.
Co-reporter:Yue Hu, Aruna Ivaturi, Miquel Planells, Chiara L. Boldrini, Alessio Orbelli Biroli and Neil Robertson
Journal of Materials Chemistry A 2016 - vol. 4(Issue 7) pp:NaN2516-2516
Publication Date(Web):2015/12/16
DOI:10.1039/C5TA09133K
The common trend in designing dyes for use in DSSCs with iodide-based electrolyte is based on a donor–π spacer–acceptor (D–π–A) architecture. Here, we report two ‘donor-free’ cyanoacrylic end-functionalized oligo(3-hexylthiophene) dyes (5T and 6T). Despite having no donor group, both dyes show reversible first oxidation process. Both 5T and 6T have n-hexyl alkyl chains to retard aggregation at different positions as well as different numbers of thiophene moieties. However, the dyes showed similar absorption properties and redox potentials. The DSSCs based on these dyes give power conversion efficiencies of more than 7%, although a significant difference in the VOC and FF has been observed. Using electrochemical impedance spectroscopy, this is attributed to the presence of more trap states when 6T attaches to TiO2 and modifies the surface, mainly affecting the fill factor. Overall, these dyes introduce a new and effective design concept for liquid-electrolyte DSSC sensitisers.
Co-reporter:Simon Dalgleish, John G. Labram, Zhe Li, Jianpu Wang, Christopher R. McNeill, Thomas D. Anthopoulos, Neil C. Greenham and Neil Robertson
Journal of Materials Chemistry A 2011 - vol. 21(Issue 39) pp:NaN15430-15430
Publication Date(Web):2011/09/05
DOI:10.1039/C1JM12466H
The synthesis and full characterisation of a novel indole-substituted nickel dithiolene [Ni(mi-5edt)2] (3) is reported, and compared to its alkyl-substituted analogue [Ni(mi-5hdt)2] (4) that has been previously communicated [Dalgleish et al., Chem. Commun., 2009, 5826] [mi-5edt = 1-(N-methylindol-5-yl)-ethene-1,2-dithiolate; mi-5hdt = 1-(N-methylindol-5-yl)-hex-1-ene-1,2-dithiolate)]. Both complexes are shown to undergo oxidative electropolymerisation, yielding polymer films that retain the redox and optical properties of the monomer. The more soluble analogue 4 is shown to form high quality thin films by spin coating, which have been utilised to fabricate field-effect transistors (FETs) and bulk heterojunction photovoltaic devices (BHJ-PVs). From FET studies, the material shows ambipolar charge transport behaviour, with a maximum carrier mobility of ∼10−6 cm2 V−1s−1 for electrons. By using 4 simultaneously as the electron acceptor as well as a NIR sensitiser in BHJ-PVs, the complex is shown to contribute to the photocurrent, extending light harvesting into the NIR region.
Co-reporter:Alexander M. Whyte, Yoshiaki Shuku, Gary S. Nichol, Michio M. Matsushita, Kunio Awaga and Neil Robertson
Journal of Materials Chemistry A 2012 - vol. 22(Issue 34) pp:NaN17975-17975
Publication Date(Web):2012/07/30
DOI:10.1039/C2JM33079B
A series of planar Ni(II), Cu(II) and Co(II) tetraaza[14]annulenes has been prepared and studied optically, electrochemically and magnetically. Thin films of each of these complexes have been prepared by vacuum deposition to evaluate the field-effect transistor (FET) performance as well as the morphology and crystallinity of the film formed. The electrochemistry and UV/Vis absorption studies indicate the materials are redox active and highly coloured, with molar extinction coefficients as large as 80000 M−1 cm−1 in the visible region. The paramagnetic complexes display weak antiferromagnetic interactions, fit to the Bonner–Fisher chain model. Each of the materials formed polycrystalline films when vacuum deposited and showed field-effect transistor behaviour, with charge carrier mobilities in the range of 10−5 to 10−9 cm2 V−1 s−1. SEM imaging of the substrates indicates that the central metal ion, and its sublimation temperature, has a crucial role in defining the morphology of the resulting film.
Co-reporter:Miquel Planells, Maddalena Pizzotti, Gary S. Nichol, Francesca Tessore and Neil Robertson
Physical Chemistry Chemical Physics 2014 - vol. 16(Issue 42) pp:NaN23411-23411
Publication Date(Web):2014/09/24
DOI:10.1039/C4CP03509G
Tricyanofuran (TCF) derivatives attached to both anthracene and pyrene moieties were synthesised and characterised by optical, electrochemical and computational techniques. Both compounds exhibited similar absorption profile as well as electrochemical behaviour, however the pyrene derivative showed 20-fold higher non-linear optical activity measured by the EFISH technique. This huge difference has been assigned to (i) a lower molar absorption and (ii) a higher torsion angle for the anthracene derivative, confirmed by both experimental X-ray diffraction and DFT calculations. Furthermore, we note that the μβ1.907 value of −1700 × 10−48 esu recorded for the pyrene derivative in CHCl3/pyridine is remarkable for a NLO chromophore lacking a classical push–pull structure.
Co-reporter:Antonio Abate, Miquel Planells, Derek J. Hollman, Vishal Barthi, Suresh Chand, Henry J. Snaith and Neil Robertson
Physical Chemistry Chemical Physics 2015 - vol. 17(Issue 4) pp:NaN2338-2338
Publication Date(Web):2014/12/04
DOI:10.1039/C4CP04685D
Two diacetylide-triphenylamine hole-transport materials (HTM) with varying redox potential have been applied in planar junction TiO2–[CH3NH3]PbI3−xClx solar cells leading to high power-conversion efficiencies up to 8.8%. More positive oxidation potential of the HTM gives higher VOC and lower JSC illustrating the role of matching energy levels, however both HTMs gave efficient cells despite a difference of 0.44 V in their redox potentials.
Co-reporter:Emily Allwright, Georg Silber, Jason Crain, Michio M. Matsushita, Kunio Awaga and Neil Robertson
Dalton Transactions 2016 - vol. 45(Issue 22) pp:NaN9368-9368
Publication Date(Web):2016/05/12
DOI:10.1039/C6DT01166G
Electrochemical deposition has been used to prepare a thin film of neutral 4′,4-(3-alkyl)-thiophene-5′,5-hydogen-nickel and copper dithiolenes (Ni–C2, Cu–C2). The application of molecular electrodeposition provides a means to solution process molecular semiconductors of poor solubility, which results from the strong intermolecular interaction required for charge transport. Both Ni–C2 and Cu–C2 form continuous thin films that show intense NIR absorptions, extending to 1800 nm and 2000 nm respectively giving evidence for the strong intermolecular interactions in the solid state. Both films are highly conducting and temperature dependence of resistance gave an activation energy of 0.42 eV and 0.072 eV respectively, with the near-metallic behaviour of Cu–C2 attributed to the additional presence of an unpaired electron.
Co-reporter:Charlotte L. Linfoot, Patricia Richardson, Tracy E. Hewat, Omar Moudam, Michael M. Forde, Anna Collins, Fraser White and Neil Robertson
Dalton Transactions 2010 - vol. 39(Issue 38) pp:NaN8956-8956
Publication Date(Web):2010/09/21
DOI:10.1039/C0DT00190B
The synthesis and subsequent spectroscopic, electrochemical, photophysical and computational characterisation of a series of heteroleptic Cu(I) complexes of general formula: [CuPOP{4,4′(R)-bipyridyl}][BF4] and [CuPOP{4,4′,6,6′(R)-bipyridyl}][BF4] is described (POP = bis{2-(diphenylphosphanyl)phenyl} ether; R = Me, CO2H, CO2Et. The steric constraint imposed by the POP ligand can impede distortion towards square planar geometry upon MLCT excitation or oxidation and this is explored in the context of varying substituents on the bipyridyl ligand. The insight gained opens new avenues for design of functional Cu(I) systems suitable for photophysical and photoelectrochemical applications such as sensitisers for dye-sensitised solar cells (DSSCs).
Co-reporter:Duncan Wass and Neil Robertson
Dalton Transactions 2011 - vol. 40(Issue 15) pp:NaN3776-3776
Publication Date(Web):2011/03/22
DOI:10.1039/C1DT90027G
A graphical abstract is available for this content
Co-reporter:Martina Congiu, Mohamed Alamiry, Omar Moudam, Serena Ciorba, Patricia R. Richardson, Laurent Maron, Anita C. Jones, Bryce S. Richards and Neil Robertson
Dalton Transactions 2013 - vol. 42(Issue 37) pp:NaN13545-13545
Publication Date(Web):2013/07/30
DOI:10.1039/C3DT51380G
Synthesis and photophysical characterisation of [Ln(hfac)3DPEPO] complexes (with Ln = Eu, Tb, Yb, Nd, Gd) has been carried out to investigate the factors responsible for the variation in total photoluminescence quantum yield within this family of emissive lanthanide complexes. Electronic absorption and emission spectroscopy, in conjunction with DFT calculations of the excited state of the Eu complex, elucidate the role of each ligand in the sensitisation of the lanthanide through the antenna effect. The X-ray crystal structure of [Gd(hfac)3DPEPO] has been determined and shows an 8-coordinate environment around the Gd and a ten-membered chelate ring involving the DPEPO ligand. Total photoluminescence quantum yields were measured to be 6%, 1% and 2% for Ln = Tb, Nd and Yb, respectively, in comparison with around 80% for Ln = Eu. The lower quantum yield for Nd and Yb, compared with Eu, can be attributed to more efficient quenching of the excited Ln state by high-energy oscillations within the ligands, whereas the lower quantum yield for Tb is assigned to a combination of poor energy transfer from the ligand excited state to the Tb and longer radiative lifetime.
Co-reporter:Tracy E. Hewat, Lesley J. Yellowlees and Neil Robertson
Dalton Transactions 2014 - vol. 43(Issue 10) pp:NaN4136-4136
Publication Date(Web):2014/01/24
DOI:10.1039/C3DT53334D
Heteroleptic neutral copper(I) dipyrrin complexes have been synthesised with the general formula [Cu(4,4′-(R)-6,6′-(CH3)-bipyridine)(dipyrrin)], R = CH3 or CO2Et, and H-dipyrrin is either 1,3,7,9-tetramethyldipyrromethene (HL1), 1,13-diphenyl-6,8-diisoindolemethene (HL2), or 1,13-diphenyl-3,11-di(trifluoromethyl)-6,8-diisoindolemethene (HL3). Improved stability was observed across the series L1–L3, likely due to better steric constraints between the ligands. Visible light absorption has also been enhanced with a red-shift in absorption from 450 nm to 600 nm. Complex 3 shows photoluminescence lifetime in the order of nanoseconds suggesting singlet fluorescence which is supported by theoretical calculations. Study of the complexes as sensitisers in dye-sensitised solar cells was achieved by assembling the dye in situ on the surface of TiO2 in a series of steps (anchoring ligand followed by ancillary ligand and [Cu(CH3CN)4][BF4]. The highest efficiency achieved was 0.41% for the dye with HL3, attributed to better dye regeneration due to a more favourable oxidation potential.
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