Precise Energy-Level Engineering of X-Shaped D-A Dyads for 1.16 s Anti-Kasha 3CT Room-Temperature Phosphorescence.

The development of charge-transfer organic room-temperature phosphorescence (3CT-ORTP) materials with second-level lifetime remains a significant challenge. Herein, we report a molecular engineering strategy using X-shaped donor-acceptor (D-A) dyads to achieve long-lived 3CT-RTP. Two isomers, axially symmetric aDOF-DBCz and centrosymmetric cDOF-DBCz, were synthesized by bridging 7H-benzo[c]carbazole (D) and 2,6-Difluorobenzonitrile (A). The X-shaped architecture expands through-space charge transfer (TSCT) pathways while lowering 3CT energy levels via LUMO delocalization across the bridging and dual acceptor units. Notably, the para-substitution in cDOF-DBCz results in a shorter D-A distance-as evidenced by NMR spatial shielding-which enhances robust TSCT interactions and minimizes non-radiative loss. As a result, cDOF-DBCz achieves an anti-Kasha 3CT-RTP τPh of 1.16 s and a ΦPh of 31% in PMMA. Furthermore, it serves as a dual-functional photoinitiator and in situ defect indicator in transparent coatings, requiring lower dosages and achieving faster curing to corresponding 3LE-RTP material. This study highlights symmetry-modulated D-A proximity as an effective design strategy for long-lived organic multi-D-A phosphors.