Donor-substituted C(sp³)-bridged phosphorus-heterotriangulenes as blue thermally activated delayed fluorescence emitters

The selective threefold para-functionalization of the dimethylmethylene-bridged phosphorus-centered heterotriangulene is achieved via an iridium-catalyzed borylation. Conversion of the borylated compound to the corresponding bromo derivative, followed by a Buchwald–Hartwig cross-coupling with aromatic amines, affords a series of donor-acceptor fluorophores in which the central phosphoryl moiety acts as a moderate electron acceptor. The compounds exhibit an intense blue photoluminescence, which is characterized by comprehensive spectroscopic studies both in solution and in thin films, supported by density functional theory calculations, as thermally activated delayed fluorescence (TADF). Especially, the carbazole-substituted compounds show considerably narrower emission bands compared to previously reported triphenylphosphine oxide-derived systems. These findings highlight the beneficial effect of the phosphorus-centered heterotriangulene on the photophysical characteristics due to its increased rigidity imparted by the C(sp³)-based bridging moieties.