Exciplex-Enhanced Singlet Emission Efficiency of Nondoped Organic Light Emitting Diodes Based on Derivatives of Tetrafluorophenylcarbazole and Tri/Tetraphenylethylene Exhibiting Aggregation-Induced Emission Enhancement

Two derivatives of tetrafluorophenylcarbazole and tri/tetraphenylethylene displaying aggregation-induced emission enhancement were synthesized and investigated by theoretical and experimental tools. The synthesized compounds exhibit efficient emission in solid state with fluorescence intensity maxima at 511 and 502 nm and photoluminescence quantum yields of 57 and 27%. They exhibit high thermal stability with 5% weight loss temperatures of 362 and 314 °C and glass-forming properties with glass-transition temperatures of 112 and 80 °C. Ionization potentials measured by photoelectron emission spectrometry were found to be comparable (5.83 and 5.87 eV). The layers of the compounds showed bipolar charge-transporting properties with balanced electron and hole mobilities reaching 10^-3 cm²/V s at high electric fields. Exciplex-host-based OLEDs containing one or two emitting layers of tetraphenylethenyl-containing emitter were fabricated and showed more than 50% higher external quantum efficiency as compared to that of the corresponding nondoped device. The best nondoped OLED containing the synthesized emitter showed turn-on voltage of 9.1 V, maximum brightness of 11 800 cd/m², maximum current efficiency of 4.5 cd/A, and external quantum efficiency of ca. 1.7%. The best modified device, with exciplex-based host layer showed turn-on voltage of 9.1 V, maximum brightness of 16 300 cd/m², maximum current efficiency of 7.3 cd/A, and external quantum efficiency of ca. 2.6%.