Dual Interface Exciplex Emission of Quinoline and Carbazole Derivatives for Simplified Nondoped White OLEDs

Isomeric quinoline and 9-phenylcarbazole derivatives with different linking topology were synthesized as versatile exciplex-forming materials. Their exciplex forming properties were examined. The studied compounds showed dual electron-donating or accepting nature and formed blue emitting excited complexes with acceptor 2,4,6-tris­[3-(diphenylphosphinyl)­phenyl]-1,3,5-triazine and orange emitting exciplexes with the donor 4,4′,4″-tris­[3-methylphenyl­(phenyl)­amino]­triphenylamine. The solutions and solid films of both the synthesized compounds showed violet fluorescence. Compound with meta-substitution exhibited higher energy of triplet level (2.64 eV) and higher ionization potential value (6.21 eV) in comparison to para-substituted one. Higher 5% weight loss and glass transition temperatures of 339 and 84 °C were observed for para-isomer. The studied compounds were characterized by bipolar charge-transport properties with hole- and electron mobilities exceeding 10–4 cm2 V–1 s–1 at electric fields exceeding 105 V/cm. White electroluminescence was achieved via combination of two interface exciplex emissions in three-layered sandwich-type OLEDs. The best fabricated and optimized nondoped device with the three-layer structure emitted white electroluminescence with a high color rendering index of 76, color temperature of 8400 K, and maximum external quantum efficiency of 3.15%.