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

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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 max values reaching 9.7% at a 5 wt% doping concentration.