Spiro Boron‐Nitrogen Molecules Based Thermally Activated Delayed Fluorescence Emitter for Highly Efficient Solution‐Processed Organic Light‐Emitting Diodes

Abstract Spiro compounds with unique structural and electronic properties are beneficial for thermally activated delayed fluorescence (TADF) emitters. Herein, a series of spiro boron‐nitrogen (B‐N) compounds are reported with donor–acceptor (D‐A) interaction through homoconjugation. Three phenyl acridine‐containing spiro B‐N compounds exhibit highly efficient photoluminescence (PL) in degassed toluene and solid‐state with obvious TADF character. The separation of HOMO and LUMO for these compounds is confirmed by theoretical calculations, as is the small Δ E ST of phenyl acridine‐containing compounds. These three compounds are used as emitting layers in solution‐processed organic light‐emitting diodes (OLEDs), resulting in deep‐blue to green emission colors with different acceptor moieties. Impressively, an excellent external quantum efficiency (EQE) of 22.1% is recorded for the TPA‐s‐ F MesBF‐based OLED device, which is comparable with the highest value from solution‐processed OLEDs based on spiro D‐A emitting materials. This work presents a facile synthetic route to novel B, N‐substituted spiro compounds, as well as the structure‐property relationship of spiro D‐A compounds for highly efficient TADF emitters.