Strategic carbazole-cycloalkyl fused donors to induce TADF featured AIE for high efficiency deep blue emission

Abstract

Aggregation-induced emission (AIE) and thermally activated delayed fluorescence (TADF) are two promising approaches in the OLED field. In the present work, we systematically engineered a carbazole unit with a substituted cyclohexyl group to develop emitters that incorporate both AIE and TADF features, thereby achieving high efficiency in the deep blue region. We functionalized the cyclohexyl-decorated carbazole donors CyCz and Cy2Cz with a phenyl triazine acceptor, resulting in the development of novel emitters, CyCzTrz and Cy2CzTrz. These emitters exhibit high T₁ and S₁ charge transfer states and demonstrate an increased photoluminescence quantum yield (PLQY) in both solution and film forms. Notably, they exhibited AIE, resulting in a threefold enhancement in emission during solvent fraction studies. Crystal analysis revealed that the AIE effect was attributed to the efficient suppression of π–π interactions among carbazole units owing to the bulkiness of CyCz and Cy2Cz. Nondoped organic light-emitting diodes (OLEDs) emitted the National Television System Committee standard blue color, with maximum external quantum efficiencies (EQEs) of 3.5% and 4.9% for CyCzTrz and Cy2CzTrz, respectively. The bis[2-(diphenylphosphino)phenyl]ether oxide-based device achieved peak EQEs of 7.1% and 14.5%, respectively. These findings can be ascribed to the TADF-mediated reverse intersystem crossing process of AIE emitters, highlighting the potential of employing an AIE-TADF material design strategy for the development of efficient OLED devices.