Molecular engineering enables efficient thermally activated delayed fluorescence emitter exceeding 1000 nm

Abstract

Restricted by the energy gap law, the development of high-performance near-infrared (NIR) thermally activated delayed fluorescence (TADF) emitters operating beyond 1000 nm remains a significant challenge. Herein, we developed a novel NIR TADF emitter, OBADC-BBPA, which features a strong intramolecular charge transfer (CT) effect through the integration of a powerful multi-sub-acceptor, 1-oxo-1H-benzo[de]anthracene-2,3-dicarbonitrile (OBADC), with the classic electron-donor biphenylphenylamine (BBPA). Driven by the strong intramolecular charge transfer (CT) effect, which enhances π-electron delocalization and lowers the LUMO energy level, the OBADC-BBPA neat film exhibits a distinctly red-shifted emission reaching 1004 nm in the NIR-II region. Quantum calculations and photophysical experiments confirmed the TADF property of OBADC-BBPA. The solution-processable NIR OLEDs based on OBADC-BBPA demonstrates “real” NIR emission (λ_onset ˃ 700 nm), featuring a peak at 933 nm and an external quantum efficiency (EQE) of 0.073 %, representing the state-of-the-art performance for solution-processable NIR-OLED using TADF emitters in similar spectral region so far. This work provides a feasible strategy of molecular design for developing real NIR TADF emitters.