A small-molecule-based boron(III)-containing donor–acceptor compound has been designed and synthesized. Interesting goldlike reflective behavior was observed in the neat thin-film sample from simple spin-coating preparation, which can serve as a potential organic thin-film optical reflector. The small thickness in nanometer range and the relatively smooth surface morphology, together with simple preparation and easy solution processability, are attractive features for opening up new avenues for the fabrication of reflective coatings. Moreover, this donor–acceptor compound has been employed in the fabrication of organic resistive memory device, which exhibited good performance with low turn-on voltage, small operating bias, large ON/OFF ratio, and long retention time.

A small-molecule-based boron(III)-containing donor–acceptor compound has been designed and synthesized. Interesting goldlike reflective behavior was observed in the neat thin-film sample from simple spin-coating preparation, which can serve as a potential organic thin-film optical reflector. The small thickness in nanometer range and the relatively smooth surface morphology, together with simple preparation and easy solution processability, are attractive features for opening up new avenues for the fabrication of reflective coatings. Moreover, this donor–acceptor compound has been employed in the fabrication of organic resistive memory device, which exhibited good performance with low turn-on voltage, small operating bias, large ON/OFF ratio, and long retention time.

A series of mononuclear and dinuclear platinum(II) terpyridine complexes with amide-, sulfonamide-, and urea-containing ligands (1–9) has been successfully designed and synthesized, and their photophysical and anion-binding properties have been studied. The anion-binding properties of the complexes were studied by electronic absorption, emission, and ¹H NMR spectroscopy. Upon the binding with anions, the dinuclear complexes 1–3 exhibit large electronic absorption and emission spectral changes, while for the mononuclear analogues 4–6 much smaller spectral changes were observed. Interesting colorimetric responses towards different anions were observed in dinuclear complexes 1–3. Dinuclear complexes 7–9 are found to be insensitive to anion-binding, which could be attributed to the presence of intramolecular Pt⋅⋅⋅Pt interactions and/or π–π stacking in the complexes that led to the reduced anion-binding affinity.

A novel class of chiral luminescent square-planar platinum complexes with a π-bonded chiral thioquinonoid ligand is described. Remarkably the presence of this chiral organometallic ligand controls the aggregation of this square planar luminophor and imposes a homo- or hetero-chiral arrangement at the supramolecular level, displaying non-covalent Pt–Pt and π–π interactions. Interestingly these complexes are highly luminescent in the crystalline state and their photophysical properties can be traced to their aggregation in the solid state. A TD-DFT calculation is obtained to rationalize this unique behavior.

A series of dithienylethene-containing boron(III) ketoiminates, as well as their corresponding β-ketoimine ligands, have been synthesized and characterized. The photophysical, electrochemical, and photochromic properties of the compounds have been studied. Photocyclization has been found to be suppressed upon introduction of a phenyl substituent on the nitrogen atom of the β-ketoiminate core, whereas photochromism could be observed by replacement of the phenyl substituent with a bulky mesityl group. It is believed that the steric effect of the mesityl unit restricts molecular rotation, resulting in such a prominent difference in the photochromic properties.

A series of newly synthesized dicyanoplatinum(II) 2,2′-bipyridine complexes exhibits self-assembly properties in solution after the incorporation of the l-valine amino units appended with various hydrophobic motifs. These l-valine-derived substituents were found to have critical control over the aggregation behaviors of the complexes in the solution state. On one hand, one of the complexes was found to exhibit interesting circularly polarized luminescence (CPL) signals at low temperature due to the formation of chiral spherical aggregates in the temperature-dependent studies. On the other hand, systematic transformation from less uniform aggregates to well-defined fibrous and rod-like structures via Pt⋅⋅⋅Pt and π–π stacking interactions has also been observed in the mixed-solvent studies. These changes were monitored by UV/Vis absorption, emission, circular dichroism (CD), and CPL spectroscopies, and morphologies were studied by electron microscopy.

Water-soluble cationic alkynylplatinum(II) 2,6-bis(benzimidazol-2′-yl)pyridine (bzimpy) complexes have been demonstrated to undergo supramolecular assembly with anionic polyelectrolytes in aqueous buffer solution. Metal–metal-to-ligand charge transfer (MMLCT) absorptions and triplet MMLCT (³MMLCT) emissions have been found in UV/Vis absorption and emission spectra of the electrostatic assembly of the complexes with non-conjugated polyelectrolytes, driven by Pt⋅⋅⋅Pt and π–π interactions among the complex molecules. Interestingly, the two-component ensemble formed by [Pt(bzimpy-Et){CCC₆H₄(CH₂NMe₃-4)}]Cl₂ (1) with para-linked conjugated polyelectrolyte (CPE), PPE-SO₃⁻, shows significantly different photophysical properties from that of the ensemble formed by 1 with meta-linked CPE, mPPE-Ala. The helical conformation of mPPE-Ala allows the formation of strong mPPE-Ala–1 aggregates with Pt⋅⋅⋅Pt, electrostatic, and π–π interactions, as revealed by the large Stern–Volmer constant at low concentrations of 1. Together with the reasonably large Förster radius, large HOMO–LUMO gap and high triplet state energy of mPPE-Ala to minimize both photo-induced charge transfer (PCT) and Dexter triplet energy back-transfer (TEBT) quenching of the emission of 1, efficient Förster resonance energy transfer (FRET) from mPPE-Ala to aggregated 1 molecules and strong ³MMLCT emission have been found, while the less strong PPE-SO₃⁻–1 aggregates and probably more efficient PCT and Dexter TEBT quenching would account for the lack of ³MMLCT emission in the PPE-SO₃⁻–1 ensemble.

A number of adamantane-containing ruthenium(II) and rhenium(I) complexes have been synthesized, characterized, and noncovalently functionalized with β-cyclodextrin-capped gold nanoparticles (β-CD–GNPs) through the host–guest interaction between cyclodextrin and adamantane. The resultant nanoconjugates have been characterized by transmission electron microscopy (TEM), energy-dispersive X-ray analysis (EDX), and 2D ROESY ¹H NMR experiments. The Förster resonance energy transfer (FRET) properties of the nanoconjugates can be modulated by both esterase-accelerated hydrolysis and competitive displacement of steroid, by monitoring the emission intensity and luminescence lifetime. The FRET efficiencies are found to vary with the nature of the chromophores and the length of the spacer between the transition metal complexes and the GNPs. This work constitutes a “proof-of-principle” assay method for the dual-functional detection of important classes of biomolecules, such as enzymes and steroids.

A novel small-molecule boron(III)-containing donor–acceptor compound has been synthesized and employed in the fabrication of solution-processable electronic resistive memory devices. High ternary memory performances with low turn-on (V_Th1=2.0 V) and distinct threshold voltages (V_Th2=3.3 V), small reading bias (1.0 V), and long retention time (>10⁴ seconds) with a large ON/OFF ratio of each state (current ratio of “OFF”, “ON1”, and “ON2”=1:10³:10⁶) have been demonstrated, suggestive of its potential application in high-density data storage. The present design strategy provides new insight in the future design of memory devices with multi-level transition states.

A series of dithienylethene-containing phosphole derivatives has been designed, synthesized and characterized. One of the compounds has been characterized by X-ray crystallography. Upon photoexcitation, the compounds exhibit drastic color changes, ascribed to the reversible photochromic behavior. Their photochromic, photophysical and electrochemical properties have been studied. They show photochromic reactivities with high photocyclization quantum yields. Their photophysical and photochromic properties are found to be facilely tuned in this system by substitution at the phosphole backbone, as well as variation on the extent of π-conjugation of the phosphole backbone. Some selected compounds have been demonstrated to exhibit photochromic properties in polymethylmethacrylate (PMMA) films.

A series of luminescent polynuclear alkynylgold(I) complexes with different lengths of alkyl chains attached at the N-heterocyclic carbene moieties has been synthesised and demonstrated to display intriguing self-assembly behaviours through a cooperative growth mechanism. Variation of the alkyl chain length was found to cause drastic morphological differences in the aggregates and to strongly affect the thermodynamic parameters as revealed by the nucleation–elongation model.

A urea-containing, (Ph₂P(R)PPh₂)-bridged, dinuclear, gold(I) thiolate complex, [Au₂{Ph₂PN(C₆H₄OMe-4)PPh₂}(SC₆H₄NHCONHC₆H₅)₂] (1) was designed and synthesized and its photophysical and anion recognition properties studied. The results show that 1 has a high selectivity toward F⁻. Upon addition of F⁻, the yellow solution was decolorized, and drastic changes of emission and ¹H and ³¹P{¹H} NMR signals were observed. Interestingly, these changes are attributed to fluoride-assisted PN bond hydrolysis, instead of the expected hydrogen-bonding interactions with the urea receptor. Similar changes were observed for two other basic anions, AcO⁻ and H₂PO₄⁻, but to a much lesser extent; and these anions were found to bind to the urea receptor at the same time. On the other hand, Cl⁻ was found to only bind to the urea moiety through hydrogen-bonding interactions. Further studies with the control complex [Au₂{Ph₂PN(C₆H₄OMe-4)PPh₂}Cl₂] (2) indicate that F⁻ assists the hydrolysis process via cleavage of the PN bond. DFT calculations were performed to study the reaction mechanism for the fluoride-assisted PN bond hydrolysis of 2; these provide a better insight into the role of fluoride in the hydrolysis.

A novel small-molecule boron(III)-containing donor–acceptor compound has been synthesized and employed in the fabrication of solution-processable electronic resistive memory devices. High ternary memory performances with low turn-on (V_Th1=2.0 V) and distinct threshold voltages (V_Th2=3.3 V), small reading bias (1.0 V), and long retention time (>10⁴ seconds) with a large ON/OFF ratio of each state (current ratio of “OFF”, “ON1”, and “ON2”=1:10³:10⁶) have been demonstrated, suggestive of its potential application in high-density data storage. The present design strategy provides new insight in the future design of memory devices with multi-level transition states.

Two-component ensembles of alkynylplatinum(II) terpyridine (tpy) complexes and carboxylic β-1,3-glucan (CurCOOH) have been investigated by using spectroscopic and microscopic techniques, as well as time-dependent UV/Vis absorption and circular dichroism (CD) experiments. Microscopic images of [Pt(tpy){CCC₆H₄(CH₂NMe₃-4)}](OTf)₂ (1) have revealed spherical nanostructures, whereas helical fibrous structures of different lengths, depending on the concentration of complex 1 and CurCOOH, were observed. The helical assemblies have been found to show low-energy metal-metal-to-ligand charge transfer (MMLCT) absorption and triplet MMLCT (³MMLCT) emission, which are indicative of Pt⋅⋅⋅Pt and/or π–π interactions between the complex 1 molecules. Interestingly, the ensemble has been demonstrated to show different handedness and even a change in handedness over time under different experimental conditions. Low temperatures, low concentrations of CurCOOH, high concentrations of complex 1, or successive addition of CurCOOH into complex 1 solution favor the formation of right-handed helical assemblies, whereas high temperatures, high concentrations of CurCOOH, low concentrations of complex 1, or single-batch addition of CurCOOH into complex 1 solution result in a fast chiroptical inversion of the ensemble solution, giving rise to the left-handed helical assemblies as the dominant species. The results have been rationalized by considering the competing kinetically and thermodynamically controlled assembly–elongation of the ensemble, which leads to the formation of right-handed and left-handed helical assemblies, respectively. The change in the handedness of the ensemble has been demonstrated to stem from the formation of two-component assemblies with supramolecular interactions, in contrast to the template- induced chiral amplification commonly observed in other systems.

A series of dithienylethene-containing triarylboranes has been designed, synthesized, and characterized. The electrochemistry, photophysics, and photochromic behavior have also been studied. The photophysical and photochromic properties could be facilely tuned in this system by varying the thiophene spacers (thiophene, thienothiophene, and bithiophene) between the dithienylethene and the dimesitylboron (BMes₂) or the position of the BMes₂ substitution in the thiophene spacers. The absorption of closed form has been found to be more sensitive towards the structural modification upon incorporation of the BMes₂ unit. Moreover, multi-addressable photochromic reactivity is obtained upon addition of Lewis base (F⁻), which is due to the formation of boron–Lewis base adduct. The dependence of the photophysical and photochromic properties on the thiophene spacers and the position of the BMes₂ substitution has been further supported by computational studies.

The exploration of phosphorescent materials based on transition metal-ligand chromophoric complexes represents an important area of research in molecular materials. The knowledge and fundamental understanding of their photophysical properties offer a possible fine-tuning of their electronic absorption and luminescence properties. The strong propensity of d⁸ transition metal compounds to form non-covalent metal···metal interactions facilitates supramolecular assembly and the formation of supramolecular nanostructures with interesting photophysical properties. The introduction of supramolecular assembly with hierarchical complexity involving non-covalent interactions could lead to research dimensions of unlimited possibilities and opportunities. This article briefly summarizes the latest progress on the use of d⁸ metal-ligand chromophores as chemosensors, as exemplified by alkynylplatinum(II) complexes with emphasis on supramolecular assembly involving non-covalent interactions, and the recent advances in the utilization of d⁸ metal-ligand phosphors, as exemplified by alkynylgold(III) system, for the exploration and development of phosphorescent OLEDs.

A novel class of luminescent platinum(II) bzimb (1,3-bis(N-alkylbenzimidazol-2′-yl)benzene) complexes has been designed and synthesized. With the incorporation of various substituents on the anionic phenyl ring of the bzimb ligand, the emission color can be readily tuned. Their photophysical, electrochemical and electroluminescence properties have been studied. These platinum(II) bzimb complexes have been demonstrated to be capable of serving as phosphorescent dopants. Efficient solution-processable OLEDs (organic light-emitting devices), with a maximum external quantum efficiency of up to 4.85 %, can be achieved. This class of platinum(II) bzimb complexes represents a promising class of phosphorescent dopants for solution-processable OLEDs.

A series of rhenium(I) diimine alkynyl complexes with various electron- and hole-transporting moieties has been synthesized and characterized. Their electronic absorption, emission and electrochemical properties have also been studied.

Molecular sensors able to detect ions are of interest due to their potential application in areas such as pollutant sequestration. Alkynylplatinum(II) terpyridine complexes with an amide-based receptor moiety have been synthesized and characterized. Their anion binding properties based on host–guest interactions have been examined with the use of UV-vis absorption and emission spectral titration studies. Spectral changes were observed for both complexes upon the addition of spherical and nonspherical anions. Their titration profiles were shown to be in good agreement with theoretical results predicting a 1:1 binding model, and the binding constants were determined from the experimental data. Drastic color changes from yellow to orange–red were observed for one of the complexes upon titration with fluoride (F⁻) ion in acetone. These changes were ascribed to the deprotonation of the amide functionalities induced by F⁻ ion, and this was confirmed by the restoration of spectral changes upon addition of trifluoroacetic acid to the F⁻ ion–complex mixture as well as by electrospray ionization mass spectrometry (ESI-MS) data.

Invited for this months cover is the group of Prof. Vivian Wing-Wah Yam, at the Department of Chemistry of The University of Hong Kong. The cover picture shows the structure of one of their alkynylplatinum(II) complexes with amide-functionalized terpyridine ligands in the present work. In their article, Margaret Ching-Lam Yeung et al. successfully demonstrated an anion sensing strategy based on the host–guest interaction between the amide-based receptor moiety and various anions by monitoring UV/Vis and emission spectral changes. In particular, drastic color changes were observed for the complex upon titration with F⁻ ions. These were ascribed to the deprotonation of the amide functionalities induced by F⁻ ions. This has been confirmed by the restoration of spectral changes upon the addition of CF₃COOH to the F^– ion–complex mixture. With such drastic color changes, this complex could be a promising candidate to serve as a probing sensor for the visual detection of F⁻ ions. For more details, see the Communication on 10.1002/open.201402019 (p. 172 ff.)

No Abstract

The synthesis, X-ray crystal structures, electrochemical, and spectroscopic studies of a series of hexanuclear gold(I) μ₃-ferrocenylmethylphosphido complexes stabilized by bridging phosphine ligands, [Au₆(PP)_n(Fc-CH₂-P)₂][PF₆]₂ (n=3, PP=dppm (bis(diphenylphosphino)methane) (1), dppe (1,2-bis(diphenylphosphino)ethane) (2), dppp (1,3-bis(diphenylphosphino)propane) (3), Ph₂PN(C₃H₇)-PPh₂ (4), Ph₂PN(Ph-CH₃-p)PPh₂ (5), dppf (1,1′-bis(diphenylphosphino)ferrocene) (6); n=2, PP=dpepp (bis(2-diphenylphosphinoethyl)phenylphosphine) (7)), as platforms for multiple redox-active ferrocenyl units, are reported. The investigation of the structural changes of the clusters has been probed by introducing different bridging phosphine ligands. This class of gold(I) μ₃-ferrocenylmethylphosphido complexes has been found to exhibit one reversible oxidation couple, suggestive of the absence of electronic communication between the ferrocene units through the Au₆P₂ cluster core, providing an understanding of the electronic properties of the hexanuclear Au^I cluster linkage. The present complexes also serve as an ideal system for the design of multi-electron reservoir and molecular battery systems.

Water-soluble alkynylplatinum(II) terpyridine complexes appended with guanidinium moieties, [Pt(tpy)(CCAr)][OTf]₂ (tpy=terpyridine; OTf=trifluoromethanesulfonate; Ar=C₆H₄-{NHC(NH₂⁺)(NH₂)}-4 (1), C₆H₄-{CH₂NHC(NH₂⁺)(NH₂)}-4 (2)), and [Pt(tBu₃tpy)(CCC₆H₄-{NHC(NH₂⁺)(NH₂)}-4)][OTf]₂ (3; tBu₃tpy=4,4′,4′′-tri-tert-butyl-2,2′:6′,2′′-terpyridine), have been synthesized and characterized. The photophysical properties of the complexes have been studied. Based on the results of UV/Vis absorption, resonance light scattering, and dynamic light scattering experiments, in aqueous buffer solutions complexes 1 and 2 undergo aggregation in the presence of citrate through strong and specific electrostatic and hydrogen-bonding interactions with citrate. The emergence of a triplet metal–metal-to-ligand charge transfer (³MMLCT) emission in the near-infrared (NIR) region brought on by the induced self-assembly of complex 1 has been demonstrated for proof-of-principle detection of citrate with good sensitivity and selectivity over other mono- and dicarboxylate substrates in the tricarboxylic acid (TCA) cycle as well as phosphate and lactate anions. Such a good selectivity toward citrate has been rationalized by the high charge density of citrate under physiological conditions and specific interactions between the guanidinium moiety on complex 1 and citrate. Extension of the work to citrate detection in fetal bovine serum and real-time monitoring of the activity of citrate lyase by the NIR emission of complex 1 have also been demonstrated.

A novel class of alkynylgold(III) complexes of the dianionic ligands derived from 2,6-bis(benzimidazol-2′-yl)pyridine (H₂bzimpy) derivatives has been synthesized and characterized. The structure of one of the complexes has also been determined by X-ray crystallography. Electronic absorption studies showed low-energy absorption bands at 378–466 nm, which are tentatively assigned as metal-perturbed π–π* intraligand transitions of the bzimpy²⁻ ligands. A computational study has been performed to provide further insights into the nature of the electronic transitions for this class of complexes. One of the complexes has been found to show gelation properties, driven by π–π and hydrophobic–hydrophobic interactions. This complex exhibited concentration- and temperature-dependent ¹H NMR spectra. The morphology of the gel has been characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM).

Two unsymmetric bipyridine–platinum(II)–alkynyl complexes have been synthesised by a post-click reaction. These metal complexes are found to exhibit emission enhancement properties. The photoluminescence quantum yield can be significantly increased from 0.03 in solution to 0.72 in solid-state thin films. Efficient solution-processable organic light-emitting diodes have been fabricated by utilizing these complexes as phosphorescent dopants. A high external quantum efficiency of up to 5.8 % has been achieved.

A novel isoquinoline-containing C^N^C ligand and its phosphorescent triphenylamine-based alkynylgold(III) dendrimers have been synthesized. These alkynylgold(III) dendrimers serve as phosphorescent dopants in the fabrication of efficient solution-processable organic light-emitting devices (OLEDs). The photophysical, electrochemical, and electroluminescence properties were studied. A saturated red emission with CIE coordinates of (0.64, 0.36) and a high EQE value of 3.62 % were achieved. Unlike other red-light-emitting iridium(III) dendrimers, a low turn-on voltage of less than 3 V and a reduced efficiency roll-off at high current densities were observed; this can be accounted for by the enhanced carrier transporting ability and the relatively short lifetimes in the high-generation dendrimers. This class of alkynylgold(III) dendrimers are promising candidates as phosphorescent dopants in the fabrication of solution-processable OLEDs.

A new class of molecular dyads comprising metalloporphyrin-linked alkynylplatinum(II) polypyridine complexes with carboxylic acids as anchoring groups has been designed and synthesized. These complexes can sensitize nanocrystalline TiO₂ in dye-sensitized solar cell (DSSC) studies. The photophysical, electrochemical, and luminescence properties of the complexes were studied and their excited-state properties were investigated by nanosecond transient absorption spectroscopy, with the charge-separated [Por^.−{(CC)Pt(tBu₃tpy)}^.+] state observed upon excitation. Excited-state redox potentials were determined; the electrochemical data supports the capability of the complexes to inject an electron into the conduction band of TiO₂. The complexes sensitize nanocrystalline TiO₂ and exhibited photovoltaic properties, as characterized by current–voltage measurements under illumination of air mass 1.5 G sunlight (100 mWcm⁻²). A DSSC based on one of the complexes showed a short-circuit photocurrent of 10.1 mAcm⁻², an open-circuit voltage of 0.64 V, and a fill factor of 0.52, giving an overall power conversion efficiency of 3.4 %.

A new series of platinum(II) complexes with tridentate ligands 2,6-bis(1-alkyl-1,2,3-triazol-4-yl)pyridine and 2,6-bis(1-aryl-1,2,3-triazol-4-yl)pyridine (N7R), [Pt(N7R)Cl]X (1–7) and [Pt(N7R)(CCR′)]X (8–17; R=n-C₄H₉, n-C₈H₁₇, n-C₁₂H₂₅, n-C₁₄H₂₉, n-C₁₈H₃₇, C₆H₅, and CH₂-C₆H₅; R′=C₆H₅, C₆H₄-CH₃-p_, C₆H₄-CF₃-p, C₆H₄-N(CH₃)₂-p, and cholesteryl 2-propyn-1-yl carbonate; X=OTf⁻, PF₆⁻, and Cl⁻), has been synthesized and characterized. Their electrochemical and photophysical properties have also been studied. Two amphiphilic platinum(II)2,6-bis(1-dodecyl-1,2,3-triazol-4-yl)pyridine complexes (3-Cl and 8) were found to form stable and reproducible Langmuir–Blodgett (LB) films at the air/water interface. These LB films were characterized by the study of their surface-pressure–molecular-area (π–A) isotherms, XRD, and IR and polarized-IR spectroscopy.

A series of platinum(II) terpyridine complexes with L-valine-modified alkynyl ligands has been synthesized. A complex with an unsubstituted terpyridine and one valine unit on the alkynyl is shown to be capable of gel formation, which is in sharp contrast to the gelation properties of the corresponding organic counterparts. Upon sol–gel transition, a drastic color change from yellow to red is observed, which is indicative of the involvement of Pt⋅⋅⋅Pt interactions. Through the concentration- and temperature-dependent UV/Vis absorption, emission, circular dichroism, and ¹H NMR studies, the contribution of hydrogen bonding, Pt⋅⋅⋅Pt and π–π stacking interactions as driving forces for gelation have been established, and the importance of maintaining a delicate balance between different intermolecular forces has also been illustrated.

A series of triarylamine-containing tricarbonyl rhenium(I) complexes, [BrRe(CO)₃(N^N)] (N^N=5,5′-bis(N,N-diaryl-4-[ethen-1-yl]-aniline)-2,2′-bipyridine), has been designed and synthesized by introducing a rhenium(I) metal center into a donor-π-acceptor-π-donor structure. All of the complexes showed an intense broad structureless emission band in dichloromethane at around 680–708 nm, which originated from an excited state of intraligand charge transfer (³ILCT) character from the triarylamine to the bipyridine moiety. Upon introduction of the bulky and electron-donating pentaphenylbenzene units attached to the aniline groups, the emission bands were found to be red shifted. The nanosecond transient absorption spectra of two selected complexes were studied, which were suggestive of the formation of an initial charge-separated state. Computational studies have been performed to provide further insight into the origin of the absorption and emission. One of the rhenium(I) complexes has been utilized in the fabrication of organic light-emitting diodes (OLEDs), representing the first example of the realization of deep red to near-infrared rhenium(I)-based OLEDs with an emission extending up to 800 nm.

Host–guest interactions of a molecular tweezer complex 1 with various planar organic molecules including polyaromatic hydrocarbons (PAHs) were investigated by 1D and 2D ¹H NMR spectroscopy, UV/Vis absorption and emission titration studies. 2D and DOSY NMR spectroscopies support the sandwiched binding mode based on 1:1 host–guest interactions. The binding constants (K_S) of complex 1 for various PAHs were determined by NMR titration studies and the values were found to span up to an order of 10⁴ M⁻¹ for coronene to no observable interaction for benzene, indicating that the π-surface area is important for such host–guest interactions. The substituent effect on the host–guest interaction based on the guest series of 9-substituted anthracenes was also studied. In general, a stronger interaction was observed for the anthracene guest with electron-donating groups, although steric and π-conjugation factors cannot be completely excluded. The photophysical responses of complex 1 upon addition of various PAHs were measured by UV/Vis and emission titration studies. The UV/Vis absorption spectra were found to show a drop in absorbance of the metal-to-ligand charge-transfer (MLCT) and ligand-to-ligand charge-transfer (LLCT) admixture band upon addition of various guest molecules to 1, whereas the emission behavior was found to change differently depending on the guest molecules, showing emission enhancement and/or quenching. It was found that emission quenching occurred either via energy transfer or electron transfer pathway or both, while emission enhancement was caused by the increase in rigidity of complex 1 as a result of host–guest interaction.

A series of dithienylethene-containing 1-thienyl-3-aryl-propane-1,3-diones (aryl=phenyl (Ph), thienyl (Th), and 4,5-bis(2,5-dimethylthiophen-3-yl)thiophen-2-yl (DTE-Th)) and the corresponding boron(III) diketonates, (O^O)BR₂ (R=F, C₆F₅, and Ph), have been designed and synthesized. Their photophysical, electrochemical, and photochromic properties have been studied. Upon coordination of a boron(III) center, the closed forms of the dithienylethene-containing β-diketonates show near-infrared response and the photochromic behavior was also found to be affected by the aryl substituents at the 3-position of the β-diketonates. Moreover, computational studies have been performed that help to provide an understanding of the effect of substituents on the photophysical and photochromic properties.

Terpyridylplatinum(II)-based metallosupramolecular triblock copolymers with hydrophilic alkynyl ligands have been synthesised and characterised. As a result of the intrinsic properties of Pluronics, reversible temperature-induced micellisation occurred at high temperature leading to aggregation of the platinum(II) complex moieties through Pt⋅⋅⋅Pt and π–π interactions, resulting in significant UV/Vis absorption and near-infrared (NIR) emission spectral changes. The critical micelle temperatures of the complexes were found to vary from 21 to 30 °C due to differences in the hydrophilicity of the alkynyl ligands and the electrostatic repulsions between the positively charged platinum(II) complex moieties. One of the complexes with pH-responsive CH₂NMe₂ groups on the alkynyl ligand was found to show NIR emission that is sensitive to both pH and temperature. Such dual-responsive behaviour has been ascribed to the modulation of the self-assembly of the complex moieties by temperature-induced micellisation and the changes in the hydrophilicity as well as electrostatic interactions upon protonation/deprotonation of the CH₂NMe₂ groups on the alkynyl ligand.

A series of luminescent platinum(II) complexes of tridentate 1,3-bis(N-alkylbenzimidazol-2′-yl)benzene (bzimb) ligands has been synthesized and characterized. One of these platinum(II) complexes has been structurally characterized by X-ray crystallography. Their electrochemical, electronic absorption, and luminescence properties have been investigated. Computational studies have been performed on this class of complexes to elucidate the origin of their photophysical properties. Some of these complexes have been utilized in the fabrication of organic light-emitting diodes (OLEDs) by using either vapor deposition or spin-coating techniques. Chloroplatinum(II)bzimb complexes that are functionalized at the 5-position of the aryl ring, [Pt(R-bzimb)Cl], not only show tunable emission color but also exhibit high current and external quantum efficiencies in OLEDs. Concentration-dependent dual-emissive behavior was observed in multilayer OLEDs upon the incorporation of pyrenyl ligand into the Pt(bzimb) system. Devices doped with low concentrations of the complexes gave rise to white-light emission, thereby representing a unique class of small-molecule, platinum(II)-based white OLEDs.

A new class of luminescent alkynylplatinum(II) complexes with a tridentate pyridine-based N-heterocyclic carbene (2,6-bis(1-butylimidazol-2-ylidenyl)pyridine) ligand, [Pt^II(C^N^C)(CCR)][PF₆], and their chloroplatinum(II) precursor complex, [Pt^II(C^N^C)Cl][PF₆], have been synthesized and characterized. One of the alkynylplatinum(II) complexes has also been structurally characterized by X-ray crystallography. The electrochemistry, electronic absorption and luminescence properties of the complexes have been studied. Nanosecond transient absorption (TA) spectroscopy has also been performed to probe the nature of the excited state. The origin of the absorption and emission properties has been supported by computational studies.

A series of cholesterol-/estradiol-appended alkynylplatinum(II) complexes with tridentate N-donor ligands, based on 2,6-bis(1-alkylpyrazol-3-yl)pyridine, has been synthesized and characterized by ¹H NMR spectroscopy, FAB-mass spectrometry, and elemental analysis. Their photophysical properties have also been investigated. Computational studies have been performed to provide insights into the nature of the electronic transitions. Some of the complexes have been found to form stable thermo- and mechanoresponsive supramolecular gels.

A series of luminescent cyclometalated platinum(II) complexes of N^C^N ligands [N^C^N=2,6-bis(benzoxazol-2′-yl)benzene (bzoxb), 2,6-bis(benzothiazol-2′-yl)benzene (bzthb), and 2,6-bis(N-alkylnaphthoimidazol-2′-yl)benzene (naphimb)] has been synthesized and characterized. Two of the platinum(II) complexes have been structurally characterized by X-ray crystallography. Their electrochemical, electronic absorption, and luminescence properties have been investigated. In dichloromethane solution at room temperature, the cyclometalated N^C^N platinum(II) complexes exhibited rich luminescence with well-resolved vibronic-structured emission bands. The emission energies of the complexes are found to be closely related to the electronic properties of the N^C^N ligands. By varying the electronic properties of the cyclometalated ligands, a fine-tuning of the emission energies can be achieved, as supported by computational studies. Multilayer organic light-emitting devices have been prepared by utilizing two of these platinum(II) complexes as phosphorescent dopants, in which a saturated yellow emission with Commission International de I′Eclairage coordinates of (0.50, 0.49) was achieved.

A new class of donor–acceptor-containing oligothienylenevinylenes with a triphenylamine donor and a dicyanovinyl group as acceptor has been synthesized and characterized. By extending the oligothiophene backbone, both the optical bandgaps and the charge-transport properties can be tuned. These oligothienylenevinylene derivatives show intense charge-transfer absorption bands that cover the entire visible spectrum, with low optical bandgaps of approximately 1.64 eV. In addition, electrochemical studies reveal that these compounds possess relatively large ionization potentials of approximately 5.5 eV. On the basis of these newly developed dicyanovinyl-substituted chromophores as donor materials and C₆₀ as acceptor material, bilayer organic photovoltaic devices have been fabricated, with the best device showing a high power conversion efficiency (PCE) of 2.0 %, with an open-circuit voltage of 0.68 V and a fill factor of 0.60 after thermal annealing. The obvious morphology change with the formation of small domains in thin films and the reduction of series resistance are believed to be responsible for the dramatic performance improvement upon thermal annealing.

Two new bichromophoric ruthenium(II) complexes, [Ru(bpy)₂(bpy-CM)](PF₆)₂ and [Ru(bpy)₂(bpy-CM343)](PF₆)₂ (bpy=2,2′-bipyridine, CM=coumarin) with appended coumarin ligands have been designed and synthesized. The energy-transfer-based sensing of esterase by the complexes has been studied by using UV/Vis and luminescence spectroscopic methods. The cytotoxicity and the cellular uptake of one of the complexes have also been investigated.

A series of multifunctional platinum(II) bipyridine complexes were designed, synthesized, and characterized by ¹H NMR, fast atom bombardment mass spectrometry (FAB-MS), and elemental analysis. Their electrochemical and photophysical properties were investigated. The photochromic properties of the spironaphthoxazine-containing complexes were also studied. Some of these complexes were shown to be capable of forming stable thermoreversible metallogels in organic solvents. In contrast to typical thermotropic organogels and metallogels, one of the complexes could form metallogels in dodecane and is very stable towards external stimuli. The photochromic activation parameters for the bleaching reaction of a representative spironaphthoxazine-containing complex in a dodecane gel were determined through kinetic studies at various temperatures. Lamellar liquid-crystalline behavior was also observed in one of the complexes, and the liquid-crystalline properties were studied by thermogravimetry analysis (TGA), polarized optical microscopy (POM), differential scanning calorimetry (DSC), variable-temperature X-ray diffraction (XRD), and variable-temperature infrared (IR) spectroscopy.

A novel class of luminescent dialkynylgold(III) complexes containing various phenylpyridine and phenylisoquinoline-type bidentate ligands has been successfully synthesized and characterized. The structures of some of them have also been determined by X-ray crystallography. Electrochemical studies demonstrate the presence of a ligand-centered reduction originating from the cyclometalating C^N ligand, whereas the first oxidation wave is associated with an alkynyl ligand-centered oxidation. The electronic absorption and photoluminescence properties of the complexes have also been investigated. In dichloromethane solution at room temperature, the low-energy absorption bands are assigned as the metal-perturbed π–π* intraligand (IL) transition of the cyclometalating C^N ligand, with mixing of charge-transfer character from the aryl ring to the pyridine or isoquinoline moieties of the cyclometalating C^N ligand. The low-energy emission bands of the complexes in fluid solution at room temperature are ascribed to originate from the metal-perturbed π–π* IL transition of the cyclometalatng C^N ligand. For complex 4 that contains an electron-rich amino substituent on the alkynyl ligand, a structureless emission band, instead of one with vibronic structures as in the other complexes, was observed, which was assigned as being derived from an excited state of a [π(CCC₆H₄NH₂)π*(C^N)] ligand-to-ligand charge-transfer (LLCT) transition.

Two series of novel platinum(II) 2,6-bis(1-alkylpyrazol-3-yl)pyridyl (N5Cn) complexes, [Pt(N5Cn)Cl][X] (1–9) and [Pt(N5Cn)(CCR)][X] (10–13) (X=trifluoromethanesulfonate (OTf) or PF₆; R=C₆H₅, C₆H₄-p-CF₃ and C₆H₄-p-N(C₆H₅)₂), with various chain lengths of the alkyl groups on the nitrogen atom of the pyrazolyl units have been successfully synthesized and characterized. Their electrochemical and photophysical properties have been studied. Some of their molecular structures have also been determined by X-ray crystallography. Two amphiphilic platinum(II) 2,6-bis(1-tetradecylpyrazol-3-yl)pyridyl (N5C14) complexes, [Pt(N5C14)Cl]PF₆ (7) and [Pt(N5C14)(CCC₆H₅)]PF₆ (13), were found to form stable and reproducible Langmuir–Blodgett (LB) films at the air–water interface. The characterization of such LB films has been investigated by the study of their surface pressure–area (π–A) isotherms, UV/Vis spectroscopy, XRD, X-ray photoelectron spectroscopy (XPS), FTIR, and polarized IR spectroscopy. The luminescence property of 13 in LB films has also been studied.

A series of photochromic spironaphthoxazine derivatives has been designed, synthesized, and characterized by using ¹H NMR spectroscopy, FAB mass spectrometry, and elemental analysis. Their photophysical and photochromic behavior have been investigated. Two of the compounds (G¹²-en-SA-SO and G¹⁶-en-SA-SO) have been shown to be capable of forming stable thermoreversible organogels in organic solvents, tested by the “stable-to-inversion of a test tube” method. Addition of p-toluenesulfonic acid was found to induce the formation of stable organogels at concentrations below that of the critical gelation concentration (c.g.c.), with a concomitant change in color from colorless to purple. Transmission electron microscopy and scanning electron microscopy of the xerogels showed typical fibrous structures in the micrometer scale. The activation parameters for the bleaching reaction of G⁸-en-SA-SO in the solution state and G¹⁶-en-SA-SO in the gel state have been determined in ethanol through kinetic studies at various temperatures. The results showed that the rate of the bleaching reaction in the gel state was much slower than that in the solution state.

A series of bis(dicyclohexylphosphino)methane (dcpm)-containing gold(I) thiolate complexes with urea receptors, 1–3, has been successfully designed and synthesized, and their photophysical and anion-binding properties have been studied. The linker between the thiolate and the urea group, and the electronic environment of the urea moiety, have been found to exert a great influence on the photophysical and anion-binding properties of the complexes. Complex 3 displays an intense long-lived orange-red luminescence at around 620 nm in the solid state and in the glass state at 77 K, which is considerably red shifted from the band seen in a solution of dichloromethane at room temperature, suggesting the presence of Au⋅⋅⋅Au interactions. Upon introducing an electron-withdrawing NO₂ group, complex 1 was found to show high selectivity and sensitivity for F⁻ through a drastic color change from yellow to red. The anion-binding constants of the complexes have been determined from electronic absorption and ¹H NMR spectroscopy titration studies and the data were found to fit well to a 1:1 binding model for the interactions between the complexes and the anions. Complexes 1 and 2 show the same anion selectivity trend of F⁻>AcO⁻>H₂PO₄⁻>Cl⁻≈Br⁻≈I⁻, which is consistent with the trend in anion basicity. In addition, complex 1 has been shown to exhibit higher binding affinity for anions compared with those of complexes 2 and 3, probably due to the higher acidity of the urea moiety as a result of the introduction of the NO₂ group.

A series of platinum(II) alkynyl-based sensitizers has been synthesized and found to show light-to-electricity conversion properties. These dyes were developed as sensitizers for the application in nanocrystalline TiO₂ dye-sensitized solar cells (DSSCs). Their photophysical and electrochemical properties were studied. The excited-state property was probed using nanosecond transient absorption spectroscopy, which showed the formation of a charge-separated state that arises from the intramolecular photoinduced charge transfer from the platinum(II) alkynylbithienylbenzothiadiazole moiety (donor) to the polypyridyl ligand (acceptor). A lifetime of 3.4 μs was observed for the charge-separated state. A dye-sensitized solar cell based on one of the complexes showed a short-circuit photocurrent of 7.12 mA cm⁻², an open circuit voltage of 780 mV, and a fill factor of 0.65, thus giving an overall power conversion efficiency of 3.6 %.

A series of dithienylethene-containing imidazolium salts with various substituents on the 2-position of the imidazolium ring has been synthesized. The photochromic properties of these compounds have been studied, and the closed forms are found to be solvatochromic due to the donor–acceptor interaction with the solvent molecules. The closed form of the imidazolium salt shows a much higher affinity towards nucleophiles over the open form of the salt. A reaction pathway has been proposed to account for this reactivity difference based on the structure–property relationship, and the possible structure of the reaction product is discussed.

A series of alkynylrhenium(I) tricarbonyl diimine complexes has been synthesized and characterized. A blue shift of the intense low-energy MLCT absorption band in the visible region was observed upon coordination of Cu^I or Ag^I. This class of complexes has been found to show rich thermotropic gelation behaviour upon Cu^I or Ag^I coordination with their morphology characterized by SEM. Their variable-temperature UV/Vis absorption and emission properties have also been studied. A blue shift in the MLCT absorption band and the switching on of luminescence were observed upon sol–gel transition.

A series of tetracyanoruthenate(II) with chelating pyridyl N-heterocyclic carbene ligands (NHC-py) was synthesized and characterized. Their photophysical and electrochemical properties as well as the photochromic behavior of their dithienylethene-containing complexes were studied. Photocyclization was found to take place upon irradiation into the metal-to-ligand charge transfer (MLCT) absorption bands of these complexes, and evidence is provided to support the triplet-sensitizing reaction pathway.

Two calixarene-based bis-alkynyl-bridged Au^I isonitrile complexes with two different crown ether pendants, [{calix[4]arene-(OCH₂CONH-C₆H₄C≡C)₂}{Au(CNR)}₂] (R=benzo[15]crown-5 (1); R=benzo[18]crown-6 (2)), together with their related crown-free analogue 3 (R=C₆H₃(OMe)₂-3,4) and a mononuclear gold(I) complex 4 with benzo[15]crown-5 pendant, have been designed and synthesized, and their photophysical properties have been studied. The X-ray structure of the ligand, calix[4]arene-(OCH₂CONH-C₆H₄CCH)₂ has been determined. The cation-binding properties of these complexes with various metal ions have been studied using UV/Vis, emission, ¹H NMR, and ESI-MS techniques, and DFT calculations. A new low-energy emission band associated with Au⋅⋅⋅Au interaction could be switched on upon formation of the metal ion-bound adduct in a sandwich fashion.

A new class of luminescent alkynylplatinum(II) complexes of tridentate bis(N-alkylbenzimidazol-2′-yl)pyridines (bzimpy), [Pt(R,R′-bzimpy)(CCR′′)]X (X=PF₆, OTf), and one of their chloro precursor complexes, [Pt(R,R′-bzimpy)Cl]PF₆, have been synthesized and characterized; one of the alkynyl complexes has also been structurally characterized by X-ray crystallography. Electrochemical studies showed that the oxidation wave is alkynyl ligand-based in nature with some mixing of the metal center-based contribution, whereas the two quasi-reversible reduction couples are mainly bzimpy-based reductions. The electronic absorption and luminescence properties of the complexes have also been investigated. In solution, the high-energy and intense absorption bands are assigned as the π–π* intraligand (IL) transitions of the bzimpy and alkynyl ligands, whereas the low-energy and moderately intense absorptions are assigned to an admixture of metal-to-ligand charge-transfer (MLCT) (dπ(Pt)π*(R,R′-bzimpy)) and ligand-to-ligand charge-transfer (LLCT) (π(CCR′′)π*(R,R′-bzimpy)) transitions. Upon variation of the electronic effects of the arylalkynyl ligands, vibronic-structured or structureless emission bands, originating from triplet metal-perturbed intraligand (IL) or an admixture of triplet metal-to-ligand charge-transfer (MLCT) and ligand-to-ligand charge-transfer (LLCT) excited states respectively, were observed in solution. Interestingly, two of the complexes showed a dual luminescence that was sensitive to the polarity of the solvents. Upon cooling from 298 K to 155 K, drastic color, UV/Vis, and luminescence changes were observed in a butyronitrile solution of 1, and were ascribed to the formation of aggregate species through Pt⋅⋅⋅Pt and π–π stacking interactions. DFT and time-dependent DFT (TD-DFT) calculations have been performed to verify and elucidate the results of the electrochemical and photophysical properties.

Polyelectrolytes carrying multiple negative charges were found to induce the aggregation and self-assembly of the positively charged platinum(II)–terpyridyl complexes in aqueous media. The aggregation and self-assembly of the complexes were driven by electrostatic interactions between the polymer and the complex, and by terpyridine ligand π–π stacking and platinum–platinum (metal–metal) interactions. As a result, remarkable UV/Vis and emission spectral changes were observed. The spectroscopic property changes were related to the structural properties of the metal complexes as well as the polyelectrolytes. The induced self-assembly of the platinum complexes was also strongly affected by the solution properties of the aqueous media, for example, the solution pH, ionic strength, and the percentage of organic solvent added.