Temperature dependent triplet-exciton relay from thermally activated delayed fluorescence (TADF) to self-sensitized triplet–triplet annihilation (TTA) of asymmetrical diphenylsulfone-based blue emitter

Abstract

The utilization of triplet excitons is greatly concerned in organic luminophores. For thermally activated delayed fluorescence (TADF) emitters, the reverse intersystem crossing (RISC) which activates the triplet excitons at low temperature remains challenging without thermal stimulation. Herein, a temperature-dependent promotion relay of the triplet excitons from TADF to self-sensitized triplet − triplet annihilation up-conversion (TTA-UC) was demonstrated in an asymmetrical TADF luminophore based on 9,9-dimethyl-9,10-dihydroacridine (DMAC) donor and diphenylfonyl (DPS) acceptor. Single-crystal structure analysis combined with theoretical calculations revealed that the alternate strong-and-weak contact of the molecules reduced the singlet–triplet splitting energy (ΔEST), amplified the singlet–triplet coupling (SOC) strength and exciton coupling (EC), leading to highly efficient RISC process over a wide range of temperatures. Moreover, benefiting from the extreme small ΔEST value and large SOC strength, highly efficient blue OLEDs were achieved with the highest CEmax, PEmax and EQEmax of 32.0 cd A-1, 33.5 lm W−1 and 14.7%, and low efficiency roll-off. This work provides a design guidance for high utilization of the triplet excitons through RISC to improve the luminescence efficiency and reduce the device efficiency roll-off.