Chromophore-labeled quinoxaline derivatives as efficient electroluminescent materials

Electroluminescent materials comprising quinoxaline, triarylamine, and fluorophores such as carbazole, pyrene, and fluorene were prepared by using a key step involving a Pd-catalyzed C-N coupling reaction. Chromophores were embedded both at quinoxaline and triarylamine units, and their influence on photophysical and thermal properties was investigated. Quinoxalines possessing more electron-donating amines exhibit lower fluorescence quantum efficiency and the photoluminescence (PL) is severely affected by the polarity of the solvent used for measurement. Bulky and rigid aromatic groups such as pyrene and carbazole enhance the glass transition temperature of the derivatives. Oxidation potential of the triarylamine was easily tuned by the aromatic substituents while retaining the reduction potential of the quinoxaline segment. This provides us a method for tuning the photophysical and thermal properties maintaining the energy levels of the dipolar compounds. The electroluminescent devices fabricated using these materials as hole-transporters and emitters led to intense light emission. The emission color is green and corresponds well with the film PL of the material used.