Managing local triplet excited states of boron-based TADF emitters for fast spin-flip process: Toward highly efficient TADF-OLEDs with low efficiency roll-off

Abstract

Abstract Improving the rate of a spin-flip process from a triplet to a singlet excited state, which is known as reverse intersystem crossing (RISC), is a challenging issue in realizing efficient and stable organic light-emitting diodes based on thermally activated delayed fluorescence (TADF-OLEDs). Herein, we report two donor−acceptor-type TADF emitters (TMCzBCO and DMACBCO) employing a boron-carbonyl (BCO) hybrid acceptor unit. The emitters possess a 3nπ* state of the BCO unit as an intermediate local triplet excited state (3LE, T2), leading to the large spin–orbit coupling between the T2 and excited singlet (S1) states with significantly low activation barriers