Azaborine as a Versatile Weak Donor for Thermally Activated Delayed Fluorescence

High Resolution Image Download MS PowerPoint Slide Extensive research has been devoted to the development of thermally activated delayed fluorescence emitters, especially those showing pure-blue emission for use in lighting and full-color display applications. Toward that goal, herein we report a novel weak donor, 1,4-azaborine (AZB), with complementary electronic and structural properties compared to the widely used dimethylacridan (DMAC) or carbazole (Cz) donors. Coupled with a triazine acceptor, AZB-Ph-TRZ is the direct structural analogue of the high-performance and well-studied green TADF emitter DMAC-TRZ and has Δ E ST = 0.39 eV, a photoluminescence quantum yield (Φ PL ) of 27%, and λ PL = 415 nm in 10 wt % doped mCP films. The shortened analogue AZB-TRZ possesses red-shifted emission with a reduced singlet–triplet gap (Δ E ST = 0.01 eV) and fast reverse intersystem crossing ( k RISC of 5 × 10 6 s –1 ) in mCP. Despite a moderate Φ PL of 34%, OLEDs with AZB-TRZ in mCP showed sky-blue emission with CIE 1931 ( x,y ) of (0.22,0.39) and a maximum external quantum efficiency (EQE max ) of 10.5%. Expanding the chemist’s toolkit for the design of blue donor–acceptor TADF materials will enable yet further advances in the future, as AZB is paired with a wider range of acceptor groups.