Pyrimidine-Based Four-Coordinate O^N^O Boron Complexes: Synthesis, Photophysical and Theoretical Studies, and TADF-Based OLED Devices.

This article describes the synthesis, along with the full photophysical and computational characterization, of a series of push-pull boron complexes comprising a sterically hindered donor connected to a pyrimidine-based O^N^O boron chelate. The dimethylacridan-functionalized fluorophore appears to be the most emissive in the series, both in toluene solution and in the solid state (as a powder), displaying thermally activated delayed fluorescence (TADF) emission in degassed media due to a small singlet-triplet energy gap. This result is in line with a previously reported pyridine analogue, which also exhibits delayed emission. Incorporation of this TADF compound into an organic light-emitting diode led to the observation of intense electroluminescence, with EQE values reaching 9.7% at a 5 wt% doping concentration.