Tuning the space and charge molecular delocalization of Highly Efficient Blue TADF Emitters Based on a 3,4,6,7,9,10-Hexahydroacridine-1,8(2H,5H)-dione Acceptor

Abstract

Development of stable and efficient blue thermally activated delayed fluorescence (TADF) emitters remains challenging due to intrinsic trade-offs among high excited-state energy, small singlet–triplet energy splitting (ΔEST), suppressed nonradiative decay, and solid-state morphological stability. A major limitation lies in the scarcity of acceptor units that simultaneously enable deep-blue emission, conformational rigidity, and resistance to aggregation-induced quenching. Here, we introduce saturated 3,4,6,7,9,10-hexahydroacridine-1,8-dione (HHAD) as an unconventional acceptor for blue TADF emitters. Unlike conventional planar acceptors, HHAD combines strong electron-withdrawing carbonyl groups with an intrinsically nonplanar and rigid framework. Two phenyl-bridged donor–π–acceptor emitters incorporating carbazole donors were designed to regulate intramolecular motion through linkage topology. Single-crystal X-ray diffraction reveals twisted donor–acceptor geometries with suppressed π–π stacking. Consequently, both emitters exhibit aggregation-induced emission, solid-state photoluminescence quantum yields exceeding 80%, and small ΔEST values down to 0.06 eV, enabling efficient reverse intersystem crossing. The neat emitter device exhibits pure blue emission with CIE coordinates of (0.179, 0.183). Upon optimization in a DPEPO host matrix, the device achieves an external quantum efficiency of 19.71%, a peak brightness of 48,859 cd m-2, and a turn-on voltage below 3.06 V. These results demonstrate that conformationally engineered HHAD acceptors offer an effective platform for high-performance blue TADF emitters.