Donor–Acceptor Boron Difluoride Complexes for Bipolar Exciplex Emitters in Organic Light-Emitting Diodes

Four 1,3-thiazole/selenazole-containing boron difluoride complexes with donor-acceptor architectures were designed, synthesized, and thoroughly spectroscopically characterized. X-ray crystallographic analysis revealed that in the solid state the molecules adopt twisted conformations that effectively suppress detrimental π-π stacking. At the same time, numerous intermolecular hydrogen-bonding interactions stabilize the packing, leading to remarkably high solid-state photoluminescence quantum yields of up to 37%. Consistent with these structural features, the dyes exhibit clear aggregation-induced emission enhancement in tetrahydrofuran-water mixtures. Beyond their photophysical properties, the complexes also demonstrate favorable semiconducting behavior. When incorporated as exciplex-forming emitters in organic light-emitting diodes, they enabled efficient device operation with external quantum efficiencies reaching up to 14.9%.