Efficient thermally activated delayed fluorescent emitter based on a spiro-type benzo[b]acridine donor and a benzophenone acceptor

Abstract

A novel spiro-type donor 5H-spiro[benzo[b]acridine-12,9′-fluorene] (SPBAC) and a thermally activated delayed fluorescence (TADF) emitter bis(4-(5H-spiro[benzo[b]acridine-12,9′-fluoren]-5-yl)phenyl)methanone (2SPBAC-BP) were synthesized for a high efficiency organic light-emitting diode (OLED). The naphthalene moiety can introduce the local excited triplet (³LE_D) state into the 2SPBAC-BP molecule. ³LE_D can enhance the spin–orbit coupling (SOC) between the lowest triplet excited state (T₁) and the lowest singlet excited state (S₁), working as an intermediate between the two charge transfer states (³CT and ¹CT) for efficient triplet exciton utilization. Using this strategy, a doped film of 20 wt% 2SPBAC-BP in the PPF host exhibits a high photoluminescence quantum yield of 72%, and the organic light-emitting diode (OLED) based on 2SPBAC-BP displays a high EQE of 26.4%, a current efficiency (CE) of 86.8 cd A⁻¹, and a power efficiency (PE) of 85.2 lm W⁻¹.