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

ABSTRACT The development of charge‐transfer organic room‐temperature phosphorescence ( 3 CT‐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 3 CT‐RTP. Two isomers, axially symmetric a DOF‐DBCz and centrosymmetric c DOF‐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 3 CT energy levels via LUMO delocalization across the bridging and dual acceptor units. Notably, the para ‐substitution in c DOF‐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, c DOF‐DBCz achieves an anti‐Kasha 3 CT‐RTP τ Ph of 1.16 s and a Φ Ph 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 3 LE‐RTP material. This study highlights symmetry‐modulated D–A proximity as an effective design strategy for long‐lived organic multi‐D–A phosphors.