Symmetry Molecular Design Strategy for Highly Efficient Blue Electroluminescence with Hot Exciton Mechanisms

Emitters with a hot exciton mechanism are regarded as one of the most promising candidates for organic light-emitting diodes (OLEDs). In this study, a deep-blue emitter with the hot exciton mechanism is reported, namely 2An-PCz, by integrating a pair of carbazole groups with a 9,9′-bi-anthracene nucleus. Owing to the symmetric molecular architecture and intrinsic local excited state character, multiple high-lying reverse intersystem cross (hRISC) channels and large overlaps of frontier molecular orbits (FMOs) can be formed, facilitating rapid hRISC processes as well as enhancement of radiative transition rates simultaneously. Combined with the strong luminescence properties brought by the unique X-packing mode, a high photoluminescence quantum yield of 60.5% is achieved in the non-doped state. Strikingly, non-doped deep-blue OLEDs exhibited a maximum external quantum efficiency (EQE) of 10.50% with minimal efficient roll-off, which is one of the highest values for deep-blue organic light-emitting devices based on hot exciton emitters thus far. The magneto-electroluminescence (MEL) experiment and transient electroluminescence measurements corroborated that both the high EQE and suppressed efficiency roll-off are attributable to the rapid “hot exciton” channels.