Tetra‐substituted Dipolar Carbazoles: Tuning Optical and Electroluminescence Properties by Linkage Variation

Abstract

Six isomeric carbazole derivatives featuring donors such as triphenylamine and carbazole and cyano acceptor are synthesized and characterized. Triphenylamine substituted compounds displayed longer wavelength absorption and emission and improved thermal stability when compared to their carbazole congeners. The compounds containing donors at 2,7‐position of carbazole core displayed negative solvatochromism in absorption while the other isomers showed solvent independent absorption profiles. Except the dye containing carbazole at 1,8‐positions, all the dyes exhibited solvatochromism in excited state. Within a series dyes containing donors at 1,8‐positions exhibited shorter wavelength absorption and emission due to the significant twisting of chromophores at 1,8‐positions. The dyes possessing donor at 2,7‐positions and cyano groups at 3,6‐positions showed best electroluminescence performance (external quantum efficiency, 4.1 %) in the series owing to their ability to utilize triplet excitons via hybridized local and charge transfer excited state.

Room-Temperature Columnar Liquid Crystals as Efficient Pure Deep-Blue Emitters in Organic Light-Emitting Diodes with an External Quantum Efficiency of 4.0%

“…The emission maxima (EL spectra) of devices were found to be almost similar to the respective solid-state PL of the emitters. It indicates the proper dispersion of the dopant into the host material with suppression of aggregation in thin films and the origin of the emission from dye molecules. , Also, we have measured the PL spectra of all synthesized compounds in the CBP host for comparison with their EL spectra (0.5 wt %) as presented in Figure S30 (see Supporting Information). It shows that the EL spectra of all the compounds closely resemble their corresponding PL spectra.…”

Recent Advances in the Design of Multi‐Substituted Carbazoles for Optoelectronics: Synthesis and Structure‐Property Outlook

“…are the two fundamental approaches often used to develop library of functional materials for optoelectronics. Unlike the conventional organic fluorophores, the functional properties such as photophysical, electrochemical, thermal and charge transport characteristics of carbazole‐based π‐conjugated materials can be fine‐tuned by its chemical modification on C1, C2, C3, C6, C7, C8 and N ‐positions [53–94] . The synthetic methods available for halogenation of carbazole at different nuclear positions are illustrated in Schemes 12345678.…”

“…reported a series of multi‐substituted cyanocarbazoles by attaching triphenylamine or carbazole chromophores through acetylene linkage ( C44 – C49 , Figure 9). [80] The 2,7‐disubstituted derivate showed negative solvatochromism in the ground state due to their dipolar character. The triphenylamine derivatives showed large magnitude of red shift in emission over the carbazole analogues (Table 3).…”

“…for the first time reported the synthesis and structure‐function relationship of poly‐functionalized carbazoles with chromophores enriched at C1,C3,C6,C8‐positions [71] . Followed by this seminal report, numerous poly‐functionalized carbazoles have been reported in the literature involving varying degrees of functionalization at C1 — C109 positions ( vide infra ) [72–100] . It has been found that poly‐functionalization on carbazole is advantageous over the di‐/tri‐functionalized carbazoles due to their improved optical, physical and electrical properties.…”

Synthesis of Solution-Processable Donor–Acceptor Pyranone Dyads for White Organic Light-Emitting Devices

“…The good performance of the device at low doping ratios may be attributed to the dilution effect, which may arise from the uniform dispersion of the dye in the employed host . At a high doping ratio, the poor performance of the device 3m may be due to charge carrier imbalance, − crystallinity of compounds, − or nonradiative excited-state decay due to Auger recombination . The device 3m exhibited pure white light emission with a maximum brightness of 922 cd m –2 at 1 wt % and CIE coordinates of (0.29, 0.31), which is possibly attributed to the balanced effect of holes and electrons within the emitting layer.…”