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%.