Azaborine as a Versatile Weak Donor for Thermally Activated Delayed Fluorescence

Extensive research has been devoted to the developmentof thermallyactivated delayed fluorescence emitters, especially those showingpure-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 comparedto the widely used dimethylacridan (DMAC) or carbazole (Cz) donors.Coupled with a triazine acceptor, AZB-Ph-TRZ is the directstructural analogue of the high-performance and well-studied greenTADF emitter DMAC-TRZ and has Delta E (ST) = 0.39 eV, a photoluminescence quantum yield (phi(PL)) of 27%, and lambda(PL) = 415 nm in 10 wt % dopedmCP films. The shortened analogue AZB-TRZ possesses red-shiftedemission with a reduced singlet-triplet gap (Delta E (ST) = 0.01 eV) and fast reverse intersystem crossing(k (RISC) of 5 x 10(6) s(-1)) in mCP. Despite a moderate phi(PL) of34%, OLEDs with AZB-TRZ in mCP showed sky-blue emissionwith CIE1931(x,y) of (0.22,0.39) and amaximum external quantum efficiency (EQE(max)) of 10.5%.Expanding the chemist's toolkit for the design of blue donor-acceptorTADF materials will enable yet further advances in the future, asAZB is paired with a wider range of acceptor groups.

Automated summary

Extensive research has been conducted to develop thermally activated delayed fluorescence (TADF) emitters with pure-blue emission. In this study, a novel weak donor, 1,4-azaborine (AZB), was synthesized and combined with a triazine acceptor to create high-performance TADF emitters. The results showed that the AZB-Ph-TRZ emitter had a photoluminescence quantum yield (phi(PL)) of 27% and emitted at 415 nm, while the shortened analogue AZB-TRZ exhibited red-shifted emission and fast reverse intersystem crossing. These findings expand the toolkit for designing blue TADF materials in the future.