Synthesis and Characterization of Novel Triphenylamine-Containing Electrochromic Polyimides with Benzimidazole Substituents

Two novel electrochromic aromatic polyimides (named as TPA-BIA-PI and TPA-BIB-PI, respectively) with pendent benzimidazole group were synthesized from 1,2-Diphenyl-N,N'-di-4-aminophenyl-5-amino-benzimidazole and 4-Amino-4'-aminophenyl-4″-1-phenyl-benzimidazolyl-phenyl-aniline with 4,4'-(hexafluoroisopropane) phthalic anhydride (6FDA) via two-step polymerization process, respectively. Then, polyimide films were prepared on ITO-conductive glass by electrostatic spraying, and their electrochromic properties were studied. The results showed that due to the π-π* transitions, the maximum UV-Vis absorption bands of TPA-BIA-PI and TPA-BIB-PI films were located at about 314 nm and 346 nm, respectively. A pair of reversible redox peaks of TPA-BIA-PI and TPA-BIB-PI films that were associated with noticeable color changed from original yellow to dark blue and green were observed in the cyclic voltammetry (CV) test. With increasing voltage, new absorption peaks of TPA-BIA-PI and TPA-BIB-PI films emerged at 755 nm and 762 nm, respectively. The switching/bleaching times of TPA-BIA-PI and TPA-BIB-PI films were 13 s/16 s and 13.9 s/9.5 s, respectively, showing that these polyimides can be used as novel electrochromic materials.

Small Molecules Containing Amphoteric Imidazole Motifs as Sensitizers for Dye-Sensitized Solar Cells: An Overview

Organic dyes, porphyrins and inorganic complexes containing imidazole (IM) motifs have been demonstrated as a new class of sensitizers in dye-sensitized solar cells (DSSCs). Particularly, the amphoteric nature of IM-based motifs allows them to be used as donors (D), auxiliary donors (D_A), linker/branch (π), or acceptors (A) in D-π-A-based organic dyes and porphyrins and also employed as cyclometalated heteroleptic and ancillary ligands in the Ru(II) and Ir(III) complexes for DSSCs. It is noteworthy that the introduction of IM chromophores in the dyes of D-π-A configuration can improve the light-harvesting properties and prohibit the charge recombination reactions due to the extension of the π-conjugated structures and hydrophobic nature. Similarly, in the case of inorganic complexes, the presence of IM motifs as ligands can improve the light-harvesting ability, give facilely tuned HOMO and LUMO energy levels, increase the charge recombination resistance and photostability. This results in enhanced photocurrent (J_SC) and photovoltage (V_OC) and consequently solar-to-power conversion efficiency (η) of DSSC devices based on Ru(II) and Ir(III) complexes. Considering the interesting DSSC applications of IM-derived molecules, in this review, we therefore comprehensively discuss their photophysical, electrochemical and photovoltaic properties reported so far and establish their structure-activity relationship to further advance the η of DSSCs. To the best of our knowledge, there is no such a review interpreting the importance of molecules possessing IM-motifs for DSSC applications to date.

New cyanopyridone-based unsymmetrical dyads: the effect of donor strength on their optoelectronic properties

Herein, we describe the design, synthesis and optoelectronic characterization of a new series of highly fluorescent dyes configured with a D-A-D' architecture, viz. CP1 to CP7. In the new molecular design, various electron-donating scaffolds were integrated with an efficient electron-accepting trialkoxyphenyl-substituted cyanopyridone moiety to study the effect of donor strength on their thermal and opto-physical properties. A detailed investigation of their thermal properties reveals that they are thermally robust with high melting and decomposition temperatures. Furthermore, in-depth photophysical studies expose their remarkable fluorescence ability in both solution and aggregated state within a wide spectral range from blue to orange. Evidently, among all the fluorophores, dyads bearing amino donors were found to be highly intense emitters due to their superior donating strength. Furthermore, solvatochromic studies showcase their ICT-dominated optoelectronic properties and it was confirmed by different correlation studies. Finally, the experimental results were correlated with their quantum chemical simulation data.

On how electron density affects the redox stability of phenothiazine sensitizers on semiconducting surfaces

The stabilities of three organic dyes that differ only by two substituents (-OMe, -H and -Br) about the phenothiazine donor unit were evaluated when immobilized on a semiconductor surface. All three dyes delivered modest power conversion efficiencies (PCEs) in the dye-sensitized solar cell (DSSC), but maintained 75% of their initial PCE over 300 h of sustained simulated sunlight. Electron-donating substituents increased the stability of the phenothiazine radical unit created after light-induced charge injection into the semiconductor; however, this did not translate to higher DSSC stability, which appears to be more sensitive to the basicity of the anchoring group for this series.

Simple adjustments to the molecular planarity of organic sensitizers: towards highly selective optimization of energy levels

Along with the specified planarization of molecular π-bridges, the LUMO levels of dyes can be effectively and selectively stabilized.

Bi-anchoring Organic Dyes that Contain Benzimidazole Branches for Dye-Sensitized Solar Cells: Effects of π Spacer and Peripheral Donor Groups

Benzimidazole-branched bi-anchoring organic dyes that contained triphenylamine/phenothiazine donors, 2-cyanoacrylic acid acceptors, and various π linkers were synthesized and examined as sensitizers for dye-sensitized solar cells. The structure-activity relationships in these dyes were systematically investigated by using absorption spectroscopy, cyclic voltammetry, and density functional theory calculations. The wavelength of the absorption peak was more-heavily influenced by the nature of the π linker than by the nature of the donor. For a given donor, the absorption maximum (λmax ) was red-shifted on changing the π linker from phenyl to 2,2'-bithiophene, whilst the dyes that contained triphenylamine units displayed higher molar extinction coefficients (ϵ) than their analogous phenothiazine-based triphenylamine dyes, which led to good light-harvesting properties in the triphenylamine-based dyes. Electrochemical data for the dyes indicated that the triphenylamine-based dyes possessed relatively low-lying HOMOs, which could be beneficial for suppressing back electron transfer from the conduction band of TiO2 to the oxidized dyes, owing to facile regeneration of the oxidized dye by the electrolyte. The best performance in the DSSCs was observed for a dye that possessed a triphenylamine donor and 2,2'-bithiophene π linkers. Electron impedance spectroscopy (EIS) studies revealed that the use of triphenylamine as the donor and phenyl or 2,2'-bithiophene as the π linkers was beneficial for disrupting the dark current and charge-recombination kinetics, which led to a long electron lifetime of the injected electrons in the conduction band of TiO2 .

New D–D–π–A type organic dyes having carbazol-N-yl phenothiazine moiety as a donor (D–D) unit for efficient dye-sensitized solar cells: experimental and theoretical studies

DSSCs using novel organic dyes (CPhTnPA, n = 0–2) with carbazol-N-yl phenothiazine moiety as a donor (D–D) unit as the sensitizers exhibited efficiency as high as 7.78% which reached 95% with respect to that of the reference N719-based device (8.20%).

Tri(N-carbazolyl)triphenylamine-based starburst organic dyes: effects of different acceptors on the optical, electrochemical and photovoltaic properties

Novel tri(N-carbazolyl)triphenylamine-based organic dyes were designed, synthesized and applied as photosensitizers for DSSCs.

Phenothiazine-based bipolar green-emitters containing benzimidazole units: synthesis, photophysical and electroluminescence properties

A series of bipolar green emitters bearing hole-transporting phenothiazine and electron-transporting N-phenylbenzimidazole are synthesized and characterized by their photophysical, electrochemical and thermal properties.