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

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 Delta EST 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-FMesBF-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. Spiro boron-nitrogen compounds with highly efficient photoluminescent properties are synthesized and exhibit typical thermally activated delayed fluorescence character both in solution and solid states. TPA-s-FMesBF exhibit excellent photo luminescent stability with almost identical photoluminescence properties in doped film and neat films, leading to an excellent EQE of 22.1% for the TPA-s-FMesBF based solution-processed organic light-emitting diode.image