Novel deep-blue hot exciton material for high-efficiency nondoped organic light-emitting diodes

Abstract

The reverse intersystem crossing (RISC) process conducted from high-energy triplet states (T_n, n ≥ 2) to singlet states (S_m, m ≥ 1), termed as the hot exciton process, has been confirmed as an efficient way to harvest the triplet excitons and achieve almost 100% exciton utilization in organic electroluminescent devices. Here, a new novel deep-blue emitter, MACN, which employs anthracene (An) as the core, and diphenylbenzene and phenyl cyanide as donor and acceptor substituents, respectively, was designed and synthesized. The photophysical study revealed that the S₁ and T₂ energy levels of MACN are close enough that the RISC from T₂ to S₁ is expected, which has been further proved by directly populating the T₂ state of MACN with an additional triplet sensitizer. Benefiting from this hot exciton triplet–singlet conversion, the non-doped deep blue-emission OLED based on MACN achieved almost 100% exciton utilization with a maximum external quantum efficiency (EQE) of 7.51%, corresponding to commission Internationale de l'Eclairage (CIE) coordinates of (0.154,0.075).