Quinoxalines incorporating triarylamines: Potential electroluminescent materials with tunable emission characteristics

Dipolar compounds featuring quinoxaline acceptors and various triarylamine donors were prepared in good yields and successfully employed in the fabrication of organic light-emitting diodes (OLEDs). It is also demonstrated that the emission color of these compounds can be easily tuned from bluish green to orange by suitably modifying the diarylamine and quinoxaline units independently. Increasing the donor and acceptor strengths bathochromically shifts the absorption and emission bands. These molecules possess moderate glass transition temperatures (114-152 degreesC) and exhibit high decomposition temperatures (441554 degreesC). The two-layer OLEDs fabricated using these materials as hole-transporting and emitting layers and 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene or tris(8-hydroxyquinolinato)aluminum as the electron-transport layer display promising characteristics, i.e., emission color, luminance, and efficiency. Incorporation of the hole-blocking quinoxaline segments in the hole-transporting triarylamine molecules leads to the confinement of the recombination zone in it, and thus emission is realized mainly from these materials for both types of devices. The factors leading to the funneling of light through the hole-transporting layer in these layers are critically analyzed.