Bis(carbazol-9-ylphenyl)aniline End-Capped Oligoarylenes as Solution-Processed Nondoped Emitters for Full-Emission Color Tuning Organic Light-Emitting Diodes

A series of bis­(3,6-di-<i>tert</i>-butylcarbazol-9-ylphenyl)­aniline end-capped oligoarylenes, BCPA-Ars, are synthesized by double palladium-catalyzed cross-coupling reactions. By using this bis­(carbazol-9-yl)­triphenylamine moiety as an end-cap, we are able to reduce the crystallization and retain the high-emission ability of these planar fluorescent oligoarylene cores in the solid state, as well as improve the amorphous stability and solubility of the materials. The results of optical and electrochemical studies show that their HOMOs, LUMOs, and energy gaps can be easily modified or fine-tuned by either varying the degree of π-conjugation or using electron affinities of the aryl cores which include fluorene, oligothio­phenes, 2,1,3-benzo­thiadiazole, 4,7-diphenyl-4-yl-2,1,3-benzo­thiadiazole, and 4,7-dithien-2-yl-2,1,3-benzo­thiadiazole. As a result, their emission spectra measured in solution and thin films can cover the full UV–vis spectrum (426–644 nm). Remarkably, solution-processed nondoped BCPA-Ars-based OLEDs could show moderate to excellent device performance with emission colors spanning the whole visible spectrum (deep blue to red). Particularly, the RGB (red, green, blue) OLEDs exhibit good color purity close to the pure RGB colors. This report offers a practical approach for both decorating the highly efficient but planar fluorophores and tuning their emission colors to be suitable for applications in nondoped and solution-processable full-color emission OLEDs

Carbazole-Dendrimer-Based Donor−π–Acceptor Type Organic Dyes for Dye-Sensitized Solar Cells: Effect of the Size of the Carbazole Dendritic Donor

A series of novel D−π–A type organic dyes, namely, <b>G<i>n</i>TA</b> (<i>n</i> = 1–4), containing carbazole dendrons up to fourth generation as a donor, bithiophene as π-linkage, and cyanoacrylic acid as acceptor were synthesized and characterized for applications in dye-sensitized solar cells (DSSCs). The photophysical, thermal, electrochemical, and photovoltaic properties of the new dyes as dye sensitizers were investigated, and the effects of the carbazole dendritic donors on these properties were evaluated. Results demonstrated that increasing the size or generation of the carbazole dendritic donor of the dye molecules enhances their total light absorption abilities and unluckily reduces the amount of dye uptake per unit TiO₂ area because of their high molecular volumes. The latter was found to have a strong effect on the power conversion efficiency of DSSCs. Importantly, electrochemical impedance spectroscopy (EIS) revealed that the size or generation of the donor had a significant influence on a charge-transfer resistance for electron recombination at the TiO₂/electrolyte interface, causing a difference in open circuit voltage (<i>V</i>_oc) of the solar cells. Among them, dye <b>G1TA</b> containing first generation dendron as a donor (having lowest molecular volume) exhibited the highest power conversion efficiency of 5.16% (<i>J</i>_sc = 9.89 mA cm^–2, <i>V</i>_oc = 0.72 V, ff = 0.73) under simulated AM 1.5 irradiation (100 mW cm^–2)