Synergy of intramolecular hydrogen bonding and π-bridge locking enables high-efficiency red/NIR electroluminescence

Abstract

Thermally activated delayed fluorescence (TADF) emitters exhibit fascinating photophysical features, yet they still suffer from unsatisfactory electroluminescence (EL) efficiencies in red/near-infrared (red/NIR) organic light-emitting diodes (OLEDs). Herein, a synergistic molecular engineering strategy combining intramolecular hydrogen bonding and π-bridge locking is exploited to develop high-performance red/NIR TADF emitters. The proof-of-concept emitter QCN-AC not only inherits the merits of the donor-π-acceptor (D-π-A) prototype (e.g., high oscillator strengths), but also features reinforced molecular rigidity to suppress non-radiative decay. Consequently, QCN-AC exhibits significantly improved exciton utilization with an excellent photoluminescence quantum yield (PLQY) of 98%, in sharp contrast to 80% for the prototype QCN-TPA. Doped red OLEDs based on QCN-AC achieve a high maximum external quantum efficiency (EQEmax) of 29.6%, representing a 1.76-fold enhancement over QCN-TPA-based device. Furthermore, this molecular engineering effectively suppresses interchromophore quenching, enabling a satisfactory EQE of 3.18% at 744 nm in non-doped NIR OLEDs, which is 1.72 times higher than that of the control device. This work not only presents a simple and effective molecular engineering for drastically boosting red/NIR EL performances, but also provides a valuable guideline for the rational development of highperformance red/NIR TADF emitters.