In this study, density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations were employed to investigate the geometries, electronic structures, reorganization energy (λ) and photophysical properties of four cyclometalated Pt(II) complexes (bzq)Pt(dpm) (1), (bzq)Pt(ppy) (2), (bzq)Pt(Ncaz) (3) and (bzq)Pt(Ndbt) (4) (where bzq = benzo[h]quinoline, dpm = dipivolylmethanoate, ppy = 2-phenylpyridine, Ncaz = N-substituted carbazole and Ndbt = N-substituted dibenzothiophene). In addition, the radiative decay processes and zero-field splitting were calculated based on the spin–orbit coupling (SOC) effect, and nonradiative decay pathways were discussed to evaluate the phosphorescence efficiency qualitatively. All the complexes retain the bzq as a cyclometalated ligand and our research focuses on the role recognition of another ancillary ligand modification theoretically. According to the results, in complexes 2–4 replacing the dpm with different ligands shows better rigidity which may weaken the nonradiative decay pathways and enhance the capability of charge transfer. Furthermore, complexes 1–4 tend to be bluish-green luminescent materials, and the emission wavelengths of 1, 2 and 4 are close to each other due to the similar excited state energy levels and electronic density distribution. Compared with complex 1, the radiative decay rate constants (kr) of 2–4 are greatly increased. Therefore, the designed complexes would be potential phosphorescence materials because of their high phosphorescence quantum efficiency and complex 3 can also serve as a promising bipolar transporting material due to its better charge transfer balance character.

•Pd(NˆCˆN)Cl is fully characterized and first proposed as two-photon Ps.•Pd(NˆCˆN)Cl can replace Pt(NˆCˆN)Cl as promising Ps due to longer T1 lifetimes.•Pd(NˆCˆN)Cl is found to be more effective and economical than Pt(NˆCˆN)Cl for PDT.Transition metal complexes capable of near-infrared light triggered-cytotoxicity are actively being developed as potential photosensitizers (PS) for photodynamic therapy (PDT) of cancers. In the present work, the structures and photophysical properties of complexes Pt(NˆCˆN)Cl and Pd(NˆCˆN)Cl (NˆCˆN = 2,6-dipyrido-4-methyl-benzenechloride) are investigated with a theoretical approach. The features of low-lying singlet and triplet excited states are discussed in detail. Their potential therapeutic use as two-photon PS in PDT is proposed on the basis of their strong absorbance in near-infrared region (NIR), vertical triplet energies resulting higher than 0.98 eV, and the spin-orbit matrix elements lager than 0.24 cm−1. Moreover, an evaluation of triplet excited states lifetime is presented. The longer lifetime of the triplet excited states would lead to higher 1O2 yields for Pd(NˆCˆN)Cl compared to Pt(NˆCˆN)Cl. It is expected that the low-cost Pd(NˆCˆN)Cl will replace the reported Pt(NˆCˆN)Cl as a promising two-photon PS for improving clinical PDT efficacy.Download high-res image (81KB)Download full-size image

•The cationic and anionic SP/MC isomerizations were investigated.•The anionic spiropyran-merocyanine isomerization is dynamic spontaneous.•In anionic isomerization, the ΔG decreased and the reaction rate increased greatly.•The BLA value reduced when the strong electron-withdrawing group substituted.Besides the photochromism isomerization, the impact of the electrochemical conditions on the spiropyran/merocyanine (SP/MC) isomerization process is also getting more and more attention. In a certain electrochemical cell, spiropyran reduced to form a radical anion and the SP/MC isomerization becomes spontaneous. Therefore, thermal reaction mechanisms for the neutral, cationic and anionic SP/MC isomerization with a series of electron-donating and electron-withdrawing groups in the 6- position of the benzopyran moiety in ground state have been systematically investigated using the density functional theory method. Some notable changes in structure, activation energy barrier and reaction rate caused by charge changes of spiropyran have been found and discussed in detail. For anionic SP/MC isomerization, due to the electron density distribution changed, the activation energy barriers decreased and the reaction rate constants of every step increased greatly. The geometrical parameter, bond length alternation (BLA), which relates to the effect of substituents, has been employed to explain the changes in the reaction mechanism induced by different electron-donating and electron-withdrawing substituents. Our results explained the control method of the small unit of the molecular machine conformational transformation process deeply from the theoretical viewpoint.Download high-res image (224KB)Download full-size image

Electrochromism with the ring-closing or ring-opening isomerization of substituted and unsubstituted bis(3-thienyl)/(2-thienyl)hexafluorocyclopentene is discussed using the DFT method. In the neutral ground state, bond making and breaking between two reactive C atoms on thienyls are thermodynamically forbidden. Under redox conditions, the gain or loss of electrons can have a significant effect on the frontier molecular orbital distribution of both open- and closed-ring isomers, particularly in reactive sites. Corresponding structural changes show a trend toward isomerization. The reaction energy barrier shows greater reduction for dication than monocation and even becomes barrierless for dianion. During the isomerization in different states, the conjugated system switches distinctively, which is attributed to the special redistribution of molecular orbitals and spin population in each state. In monocation and monoanion, for the involvement of a single electron, isomerization is inclined to proceed sequentially between right and left thienyls, whereas it becomes synchronous in dication. The direction depends on the stabilization achieved by the formation of a global conjugated system and more average spin population on the molecule. The effect of substituents on thienyls is demonstrated in the promotion of the extent of conjugation and the determination of the spin population level on the reactive C atoms. Moreover, according to their electron-donating and withdrawing abilities, they can kinetically support or suppress the electron transfer pattern in the process from isomer to transition state, which leads to the control of reaction efficiency.

•Thermal cis-trans isomerization of few azo compounds have been investigated.•There are inversion mechanism and rotation mechanism for these compounds.•The electron donation groups change the isomerization reaction parameters.•Calculated half-lives are in qualitative agreement with experimental values.Thermal cis→trans isomerization for a series of BF2-coordinated azo compounds of the para-substitution with electron donating groups have been systematically investigated. The density-functional theory calculations exhibited good performance to provide better understanding of the effects of para-substitution with electron donating groups. It is found that the different electron donation groups can significantly affect the absorption spectra, the energy levels of molecular orbitals, the transition properties for the trans isomers, the rate constants and the half-lives for the thermal cis→trans isomerization. Our calculated half-lives for the thermal cis→trans isomerization are in qualitative agreement with the experimental values. Specifically, we have evaluated the thermal rate constants at 294 K. The relationship between the thermal isomerization and the para-substituted electron-donating group reveals that the inversion mechanism is preferred for the substituent species while the rotation mechanism is more favorable for non-para-substituent molecule.

Density functional theory and time-dependent density functional theory investigations were performed on the geometrical structures, basic photophysical properties, phosphorescence quantum efficiency (Φ PL), and reorganization energy (λ) calculations of a new potential class of tetradentate Pt(II) complexes Pt[ppz-O-Popy] (1) (where ppz = phenyl-pyrazole; Popy = phenoxyl-pyridine), Pt[pmi-O-Popy] (2) (where pmi = phenyl-methylimidazole), Pt[pmi-O-Cbpy] (3) (where Cbpy = carbazolyl-pyridine) and Pt[ppz-O-Cbpy] (4), which show highly efficient (ΦPL > 80%) and deep-blue emission. Nonradiative decay processes were investigated in order to obtain a more reliable nonradiative decay rate comparison. The calculated results confirm that tetradentate Pt(II) complexes are conducive to maintaining the rigidity of the molecules. The extended conjugation complexes with carbazole groups in 3 and 4 can not only improve the structural rigidity but also enhance the capability and balance of charge transfer. Thereupon, the following two designed derivatives Pt[pmi-O-Cbmi] (5) and Pt[pmi-O-Cbbm] (6) which substitute pyridine with imidazole and benzimidazole based on complexes 3 and 4 are also considered for promising materials exploitation and theoretical understanding. The charge transfer balance performance and the radiative decay rate constant (kr) of 5 and 6 are greatly improved compared with 1–4, and the better structural rigidity will weaken nonradiative decay pathways, which may result in a higher phosphorescence quantum efficiency. Therefore, complexes 5 and 6 through judicious molecular design will be promising candidates as highly efficient blue-emitting phosphorescent materials for applications.

•We use a dye–TiO2–electrolyte model to investigate the regeneration process.•Three electrolyte components (I−, I2, I3−) have been considered in this study.•Dye–iodine interaction was discussed in both ground state and excited state.•Dye regeneration would greatly influence the electronic stimulation and injection.We report a theoretical study to ascertain dye regeneration in dye sensitized solar cells (DSSCs) with the TiO2–dye–electrolyte model. Oxidized 3-(5-(4-(diphenylamino)styryl)thiophen-2-yl)-2-cyanoacrylic acid (L2) dye, three electrolyte main components (I−, I2, I3−) and (TiO2)9 cluster has been selected in this model. The calculated results show that the combination capability of electrolyte to L2+@TiO2 is according to the order of I− > I3− > I2. Furthermore, oxidized dye together with electrolyte can get good performance of absorption in visible light region. Specifically, I− may accelerate the electronic transition and injection by participating in the positive charge transfer. I2 may lead to the opposite transition and I3− ions seem to be a mixed result of both effects. In this study, the charge transfer pathway during dye regeneration process has been found. It can be predicted that the charge transfer of dye regeneration may contribute to the absorption in UV–vis region of DSSC.

•The ring-opened Zn tetrapyrrin has a helical geometry.•The Q-band of Zn tetrapyrrin is red-shifted and intense compared to zn porphyrin.•Fluorescence intensity is higher for Zn tetraphyrin than Zn porphyrin.Exploring the relationship between the geometrical structures and spectral properties has great significance to design some desirable materials. For important pyrrole contained macromolecules, there is a new complex of Zn tetrapyrrin with opened chain ligand derived from breaking one methine bridged of Zn porphyrin. The frontier molecular orbitals, absorption and emission properties of such Zn tetrapyrrin complexes are investigated by density functional theory (DFT) and its time-dependent density functional theory (TD-DFT) methods. Compared to Zn porphyrin, the HOMOs and LUMOs are no longer degenerate, the lowest lying absorption and emission of Zn tetrapyrrin start to increase in intensity with the shifting of charge transfer transition band to near-infrared region. We hope these theoretical studies will assist the design of novel molecular materials.

•The organic D-A-π-A dyes with different π space were designed for DSSCs.•The absorption spectra of dyes before/after binding to TiO2 clusters were studied.•The D-A-π-A dyes had indirect electron injection mode.•The DPP leads to red shifted of absorption band with higher oscillator strength.•The DPP group directly linked with the donor part was favor for electron injection.A series of organic donor-π-acceptor dyes with difference in π spacer have been designed and investigated theoretically as sensitizers for application in dye-sensitized solar cells. Density functional theory and time-dependent density functional theory calculations reveal how the additional electron-withdrawing diketopyrrolopyrrole unit and π spacer order influence the physical properties of the dyes, including spectral response, light harvesting efficiency, and electron injection rate. The results show that auxiliary acceptor leads to the greatly red-shifted of the charge-transfer absorption band. Meanwhile, the number and sort order of thiophene groups can significantly tune the orbital energy levels and change the electronic transition processes. The thiophene groups locating between triphenylamine and diketopyrrolopyrrole units would conduce to the light absorption and electron injection efficiency. The results also suggest that the donor-acceptor-π-acceptor type dyes have indirect electron injection mode compared with the direct mode in the dyes without containing diketopyrrolopyrrole.

In this work, the effect of regulated host and auxiliary ligand π-conjugation on the photophysical properties of a series of Ir(III) carbene complexes is examined by using the start-of-the-art theoretical methods. According to our results, all of the lowest-lying and strongest absorption peaks can be assigned as having a mixed ligand-to-ligand/metal-to-ligand charge transfer (LLCT/MLCT) character, but the different ways of introducing phenyl have a great effect on the absorption wavelength variation. In addition, the charge transfer characteristics of lowest-lying emission have some minute differences. In addition, when the extended π-conjugation is broken, the emission wavelength can be effectively retained due to the similar emission charge transfer related electronic density distribution of occupied molecular orbitals and unoccupied molecular orbitals. However, the larger π-conjugation can give rise to remarkably blue-shifted emission. This blue-shifted emission can be attributed to the alteration in the transition character due to intense interactions between nearly degenerate unoccupied molecular orbitals. Through the evaluation of the spin–orbit coupling (SOC) effect, we can gain a deeper understanding of the radiative decay rate processes. These results reveal that the larger π-conjugation can also lead to higher quantum efficiency due to the larger radiative decay and the smaller nonradiative decay rate. Our theoretical studies highlight the role of π-conjugation of the host and auxiliary ligand, and thus, can pave the way for the design of novel and efficient blue phosphorescent materials.

Dye sensitizers play an important role in dye-sensitized solar cells (DSSCs). Owing to the synthetic challenge and cost of precious metal-complex dyes, increasing research has been focused on organic molecule dyes, porphyrin and light metal porphyrin dyes. In this paper, three natural porphyrin derivatives as dyes with the TiO2 nanoparticulate model are studied theoretically using density functional theory (DFT) approaches to explore their spectroscopic properties and application future in DSSCs. The detailed orbital components and absorption transitions of these porphyrin derivatives are analyzed from the calculated results. Key parameters of the short-circuit current density (Jsc) including light harvesting efficiency (LHE), electron injection driving force (ΔGinject) and nonlinear optical properties (NLO) were discussed. In addition, the calculated values of open circuit photovoltage (Voc) for these dyes were also presented. The tetrapyrrole macrocycle of porphyrin with central metals Mg or Zn can enrich the absorption strength greatly. Our research reveals that the Zn–porphyrin sensitizer can be used as a potential sensitizer for DSSCs due to its good electronic and optical properties and good photovoltaic parameters. This study is expected to understand natural dye sensitizers and assist the molecular design of new dyes for further DSSC improvement.

•Dye YD2-O-C8 with different electric field strength are investigated theoretically.•The absorptions of dye with different electric field are narrowing and blue shifted.•Some reasonable explanations on the influence of the electric field have provided.•This work can provide a better understanding for the operating principles of DSSC.The local electric field formed between dye sensitizers and semiconductor interface is one of key factors to determine the overall performance of dye-sensitized solar cells (DSSCs). Herein, a strategy has been proposed to explore the influence of the local electric field on the functionality of DSSCs of YD2-O-C8 dye via calculating the relevant properties in various electric field strengths. The YD2-O-C8 dye has been systemically studied with density functional theory (DFT) and time-dependent DFT (TD-DFT) for its electronic structure and optical properties in tetrahydrofuran (THF) solution. The absorption spectra are gradually narrowing and blue-shifting while increasing the electric field strength. Two key parameters of the light harvesting efficiency (LHE) and the TiO2 conduction band shift (ΔEcb) have been examined for the YD2-O-C8 sensitized TiO2 system. It is found that it is of great importance to reduce the charge accumulation on the TiO2 film, which lowers the electric field strength and shows the best performance of DSSCs. This study is expected to deepen our understanding of the function of local electric field and the operational principles of the DSSCs for further optimization.

Density functional calculations have been explored to analyze the structural, electronic and charge transfer properties of a doped TiO2 substrate and catechol–TiO2 interfaces for dye-sensitized solar cells. The results demonstrate that the dopant W6+ moves the CB (conduction band) edge downward and introduces 5d-unoccupied orbitals located in the CB bottom of the TiO2. On the other hand, the dopant Zn2+ shifts the CB edge upward with an insertion of 3d-occupied orbitals into the VB (valence band). In catechol–TiO2 systems, W6+ enlarges the energy difference between the LUMO of catechol and LUMO of TiO2, which enlarges the driving force for electron injection in turn and results in an increased short circuit current (Jsc). Our modeling injection dynamics and quantitative Bader analysis of the interfacial charge transfer have revealed that the catechol–TiO2 doped with W6+ provides faster and more electron injection for dye sensitized solar cells (DSSCs). While the Zn2+ doped system exhibits lower electron efficiency due to the minimized energy difference between the catechol LUMO and TiO2 CB.

The molecular aggregation structure of three D–A cocrystal complexes based on substituted distyrylbenzenes (DSB) was studied by density functional theory calculations. The influence of molecular stacking on molecular interactions, frontier molecular orbitals, charge transport and photophysical properties has been investigated in depth, by comparison of D1–A1, D2–A2 and D2–A2′ pairs with different substituents in D and A monomers. Our results provide not only a better understanding of the relationship of the D–A configuration and electrical/optical properties, but also the theoretical prediction of novel organic semiconductor materials for the mixed-stack D–A charge-transfer crystal. In particular, the charge-transfer complexes of D1–A1 have been demonstrated as a good ambipolar material, while the complexes of D2–A2 and D2–A2′ should conduct as better n-type organic semiconductor materials.

•A series of Ir (III) complexes were investigated by DFT and TD-DFT method.•The Ir complexes appeared here have an advantage of low efficiency roll-off property.•The materials appeared here are practical for OLED industrialization.A series of heteroleptic cyclometalated Ir (III) complexes for OLEDs application have been investigated theoretically to explore their electronic structures and spectroscopic properties. The geometries, electronic structures, and the lowest-lying singlet absorptions and triplet emissions of (piq)2Ir(acac) (labeled 1) and theoretically designed models (piq)2Ir(dpis) (labeled 2), (4Fpiq)2Ir(dpis) (labeled 3), (4F5M-piq)2Ir(dpis) (labeled 4), (4,5-2F-piq)2Ir(dpis) (labeled 5) and (5-F-piq)2Ir(dpis) (labeled 6) were investigated with density functional theory (DFT)-based approaches, where, piq = 1-phenylisoquinolato, acac = acetylacetonate and dpis = diphenylimidodisilicate. Their structures in the ground and excited states have been optimized at the DFT/B3LYP/LANL2DZ and TDDFT/B3LYP/LANL2DZ levels, and the lowest absorptions and emissions were evaluated at B3LYP and M062X level of theory, respectively. Furthermore, the energy-transfer mechanism of these complexes also be analyzed here, and the result shown that the complexes 1–6 are having the low efficiency roll-off property. Except that, the oscillator strength analyze shown that the complexes 2–6, which were designed by theory, are suitable for OLED since their high oscillator strength property.Graphical abstract

The ring-closing reaction commonly occurs at the lowest singlet excited state when the open-form dithienylethene is irradiated at about 300 nm. A lower-energy light, at 425 nm, can also elicit this ring-closing reaction when there is a connection between the dithienylethene and platinum-terpyridyl segment to form a complex through an ethynyl linker or an ethynyl-ether linker. Through the calculation of the energy levels, we propose the ring-closing process as follows. The light absorbed by the platinum-terpyridyl unit excites the molecule to a singlet excited state. Meanwhile, this electronic state of the molecule transfers to the lowest triplet excited state through intersystem crossing and internal conversion. When energy is asborbed from the environment, this state goes up to a higher triplet state around the dithienylethene part, where the ring-closing reaction takes place. Moreover, different patterns of linkers bring about different efficiency of the reaction, and a direct shared linker may facilitate the ring-closing process. In addition, the conjugated linker also causes the maximum wavelength of the complex to red shift because the energy gap between the involved frontier molecular orbitals becomes lower.

•The calculated stabilities of the isomers are in this order FGoDTEo > FGcDTEo > FGoDTEc > FGcDTEc.•The absorption at 366 nm results the cyclization of both ring-open isomers of FG and DTE.•The theoretical analysis explains the characteristics of the lowest-energy absorptions of FGDTE.•The work provides some guides in encoder-molecule design.A molecule consisting of one dithienylethene covalently linked to two fulgimide photochromes has been designed as a 4-to-2 encoder. The combined molecule has four stable isomers, one may convert to another by particular irradiations. In this paper, we calculated the Gibbs free energies of the four isomers and got the order of their stabilities. Then the mechanisms of ring-opening and ring-closing of the monomers were explored in detail and the reaction conditions for structural conversion were also discussed. The corresponding absorption spectra of the combined molecules were researched and the new characters in the designed systems were predicted as well. Finally, we optimized their corresponding excited-state structures and analyzed the emission properties.

DSSCs have been extensively investigated in the past decade, and the search for more efficient dyes for DSSCs remains challenging. In this work we discuss the influences of elongating π-spacers and rigidifying dithiophene on the performance of dithiafulvenyl (DTF)-based organic dyes using density functional theory (DFT) and time-dependent DFT methods. We show that systematically elongating the π-spacer of the DTF-2P dye by increasing the number of thiophene groups tends to red-shift the absorption peak and broaden the absorption range, thus improving the light-harvesting efficiency of DTF-2P-T and DTF-2P-2T. Furthermore, among the three dyes, DTF-2P-T would have the best performance because it performs nicely on the key parameters including the electron injection driving force (D), the light-harvesting efficiency (LHE), and the shift of the TiO2 conduction band (ΔEcb). In particular, DTF-2P-2T has a larger LHE despite the smaller D and ΔEcb compared with DTF-2P-T. Having realized the great merits of modification on π-spacers, afterwards, we designed a novel dye by rigidifying the dithiophene moiety of DTF-2P-2T. The resulting dye is proven to be very promising to challenge the conversion efficiency 8.29% of DTF-2P-T due to the improved ΔEcb and LHE. Our theoretical studies are expected to provide valuable insights into the molecular design of novel DTF-based dyes for the optimization of DSSC.

The adsorption of hydroxamate onto a TiO2 anatase surface has been theoretically determined. We find that the doubly deprotonated configuration is the optimal adsorption mode in terms of energetic and dynamical stability, which is demonstrated by vibrational spectrum analysis. This configuration can also undergo the ultrafast electron transfer event, with a time-scale of 53 fs.

D–A–π–A dyes have exhibited several excellent advantages including optimized energy levels, and distinct improvement of photovoltaic performance and stability. By modulating the auxiliary acceptor and acceptor unit, the efficiency of D–A–π–A dye based dye-sensitized solar cells can be further improved. Based on density functional theory methods, sixteen dimethoxyl-substituted triphenylamine based D–A–π–A dyes composed of different acceptor and auxiliary acceptor groups were designed, meanwhile for reference four homologous D–π–A dyes were also compared in this work. The properties of all the dyes, including intramolecular charge transfer, light harvesting efficiency, kinetics of electron injection, and vertical dipole moment, have been investigated theoretically to identify the dyes which would produce high efficiency. Then the interaction between the selected dyes and the electron acceptor in the electrolyte was discussed to reveal the interfacial charge recombination process. In comparison with other dyes, TNA4 displays outstanding performance due to its key parameters to achieve a balance between competing factors. Compared with cyanoacrylic acid, 2-(1,1-dicyanomethylene) rhodanine group can serve as an excellent acceptor for future DSSCs applications.

We report, from a theoretical point of view, the first comparative study between the highly water-stable hydroxamate and the widely used carboxylate, in addition to the robust phosphate anchors. Theoretical calculations reveal that hydroxamate would be better for photoabsorption. A quantum dynamics description of the interfacial electron transfer (IET), including the underlying nuclear motion effect, is presented. We find that both hydroxamate and carboxylate would have efficient IET character; for phosphate the injection time is significantly longer (several hundred femtoseconds). We also verified that the symmetry of the geometry of the anchoring group plays important roles in the electronic charge delocalization. We conclude that hydroxamate can be a promising anchoring group, as compared to carboxylate and phosphate, due to its better photoabsorption and comparable IET time scale as well as the experimental advantage of water stability. We expect the implications of these findings to be relevant for the design of more efficient anchoring groups for dye-sensitized solar cell (DSSC) application.Keywords: anchoring groups; DSSC; nuclear dynamics; optical properties; quantum dynamics;

We report a DFT study of interaction between the Ru complex sensitizer [Ru(dcbpy)2(NCS)2: dcbpy = 4,4′-dicarboxy-2,2′-bipyridyl] (N3) and iodide ion under the influence of different deprotonation situations. There are two kinds of interaction mechanisms: iodide ion interacts with metal-center Ru atom or carboxyl, derived from the natural charge distribution analysis. The calculation indicated that there were several stable intermedium forms in different deprotonation degree. The stability of these intermedium forms would be perturbed gradually while the number of eliminated protons increased. It can be predicted that in the initial period of absorption and injection as well as the dissolve process where the deprotonation was demanded, the dye will not attacked by the iodide ion in solution extensively. Additionally, dye with more carboxyls will reduce the activity of redox reaction and more obstacles are required to be overcome before or during the redox reaction. The comparison of natural charge between isolate N3 and N3 with iodide ion intermedium (N3I–) showed the iodide ion attacking made the charge contribute on N3 molecule more negative, nevertheless the N3I– still has ability to attract another iodide ion. The attacking of iodide ion will also influence the electronic transition and absorption properties through the analysis of the frontier molecular orbitals and the densities of states. The results reported in this paper give us the guidance to carry out the further investigations about the dye regeneration process.

DSSCs have been extensively investigated in the past decade, and the search for more efficient dyes for DSSCs remains challenging. In this work we discuss the influences of elongating π-spacers and rigidifying dithiophene on the performance of dithiafulvenyl (DTF)-based organic dyes using density functional theory (DFT) and time-dependent DFT methods. We show that systematically elongating the π-spacer of the DTF-2P dye by increasing the number of thiophene groups tends to red-shift the absorption peak and broaden the absorption range, thus improving the light-harvesting efficiency of DTF-2P-T and DTF-2P-2T. Furthermore, among the three dyes, DTF-2P-T would have the best performance because it performs nicely on the key parameters including the electron injection driving force (D), the light-harvesting efficiency (LHE), and the shift of the TiO2 conduction band (ΔEcb). In particular, DTF-2P-2T has a larger LHE despite the smaller D and ΔEcb compared with DTF-2P-T. Having realized the great merits of modification on π-spacers, afterwards, we designed a novel dye by rigidifying the dithiophene moiety of DTF-2P-2T. The resulting dye is proven to be very promising to challenge the conversion efficiency 8.29% of DTF-2P-T due to the improved ΔEcb and LHE. Our theoretical studies are expected to provide valuable insights into the molecular design of novel DTF-based dyes for the optimization of DSSC.

By employing two types of hydrothermal in situ ligand reactions (acylation of N2H4 with aromatic polycarboxylic acids, reduction of 3-nitrophthalhydrazide by N2H4), three new acylhydrazidate-extended Zn2+ coordination polymers [Zn2(3-apth)(atrz)2] (3-apth = 3-aminophthalhydrazidate; atrz = 3-amino-1,2,4-triazolate) 1, [Zn2(4-apth)(atez)2] (4-apth = 4-aminophthalhydrazidate; atez = 5-aminotetrazolate) 2, and [Zn(3-cppth)(H2O)] (3-cppth = 4-(3-carboxyphenoxy)phthalhydrazidate) 3 were obtained. X-ray single-crystal diffraction analysis revealed that (i) compound 1 possesses a 3-D structure. The triazolate molecules link the Zn2+ ions to form a 2-D layer with a (6,3) topology. Then the acylhydrazidate molecule acts as the second linker, extending the (6,3) nets into a 3-D network of compound 1; (ii) compound 2 also exhibits a 3-D structure. The acylhydrazidate molecules first link the Zn2+ ions into a 1-D infinite chain. The tetrazolate molecules propagate further the chains into a 3-D (4,4)-connected net (symbol: (4·64·8)2(42·62·82)); (iii) compound 3 only shows a 1-D chain structure. The photoluminescence analysis indicates that the three title compounds all emit light, especially compound 2 which emits extremely strong blue light. The side group on the phthalhydrazidate molecule plays a crucial role in the emission behaviors of compounds 1–3. At 77 K, the activated compound 2 can adsorb N2 with a capacity of ca. 41.0 cm3 g−1.

In this work, the effect of regulated host and auxiliary ligand π-conjugation on the photophysical properties of a series of Ir(III) carbene complexes is examined by using the start-of-the-art theoretical methods. According to our results, all of the lowest-lying and strongest absorption peaks can be assigned as having a mixed ligand-to-ligand/metal-to-ligand charge transfer (LLCT/MLCT) character, but the different ways of introducing phenyl have a great effect on the absorption wavelength variation. In addition, the charge transfer characteristics of lowest-lying emission have some minute differences. In addition, when the extended π-conjugation is broken, the emission wavelength can be effectively retained due to the similar emission charge transfer related electronic density distribution of occupied molecular orbitals and unoccupied molecular orbitals. However, the larger π-conjugation can give rise to remarkably blue-shifted emission. This blue-shifted emission can be attributed to the alteration in the transition character due to intense interactions between nearly degenerate unoccupied molecular orbitals. Through the evaluation of the spin–orbit coupling (SOC) effect, we can gain a deeper understanding of the radiative decay rate processes. These results reveal that the larger π-conjugation can also lead to higher quantum efficiency due to the larger radiative decay and the smaller nonradiative decay rate. Our theoretical studies highlight the role of π-conjugation of the host and auxiliary ligand, and thus, can pave the way for the design of novel and efficient blue phosphorescent materials.

Electrochromism with the ring-closing or ring-opening isomerization of substituted and unsubstituted bis(3-thienyl)/(2-thienyl)hexafluorocyclopentene is discussed using the DFT method. In the neutral ground state, bond making and breaking between two reactive C atoms on thienyls are thermodynamically forbidden. Under redox conditions, the gain or loss of electrons can have a significant effect on the frontier molecular orbital distribution of both open- and closed-ring isomers, particularly in reactive sites. Corresponding structural changes show a trend toward isomerization. The reaction energy barrier shows greater reduction for dication than monocation and even becomes barrierless for dianion. During the isomerization in different states, the conjugated system switches distinctively, which is attributed to the special redistribution of molecular orbitals and spin population in each state. In monocation and monoanion, for the involvement of a single electron, isomerization is inclined to proceed sequentially between right and left thienyls, whereas it becomes synchronous in dication. The direction depends on the stabilization achieved by the formation of a global conjugated system and more average spin population on the molecule. The effect of substituents on thienyls is demonstrated in the promotion of the extent of conjugation and the determination of the spin population level on the reactive C atoms. Moreover, according to their electron-donating and withdrawing abilities, they can kinetically support or suppress the electron transfer pattern in the process from isomer to transition state, which leads to the control of reaction efficiency.

It is well-known that the inner electric field formed between the counter electrode and the semiconductor surface has a substantial effect on the efficiencies of dye-sensitized solar cells (DSSCs). To reveal the function of the inner electric field for different types of porphyrin sensitizers in DSSCs, the properties of three types of porphyrin sensitizers (α, β, and center axial positions) under different electric fields were calculated by using density functional theory (DFT) and time dependent density functional theory (TD-DFT). The electronic structures and optical properties of these studied dyes in tetrahydrofuran (THF) solution were also investigated correspondingly. Key parameters of the short-circuit current density (Jsc) including light harvesting efficiency (LHE), electron injection driving force (ΔGinject) and intramolecular charge transfer (ICT) were detailedly discussed. The results show that the a-position type porphyrin sensitizer can be used as a potential sensitizer for DSSCs under an enhanced electric field. We expect that the present study would deepen the understanding of the function of an inner electric field and may be helpful in DSSC design in the future.