Pyrazino[2,3-f][1,10]phenanthroline Derivatives as Robust Photocatalysts Enabling ppm-Level Organocatalyzed Photoinduced Electron/Energy Transfer Reversible Addition–Fragmentation Chain Transfer Polymerization

Exploring high-performance organic photocatalysts (PCs) for photoinduced electron/energy transfer reversible addition–fragmentation chain transfer (PET-RAFT) polymerization represents a cutting-edge research field. In this study, six donor (D)–acceptor (A) type organic PCs based on the pyrazino[2,3-f][1,10]phenanthroline structure were designed and synthesized, showcasing their successful application in PET-RAFT polymerization. Furthermore, diverse substituent groups were introduced to enable precise control over the photophysical and electrochemical properties of organic PCs. Time-dependent density functional theory (TD-DFT) analysis further identified two organic PCs (PCs 5 and 6) that exhibit thermally activated delayed fluorescence (TADF) characteristics. PCs 5 and 6 demonstrated high molar extinction coefficients (εmax) and long delayed fluorescence (DF) lifetimes, achieving high-efficiency photopolymerization even at catalyst loadings as low as 0.1–10 ppm. This study elucidates the structure–activity correlation of such organic PCs while underscoring the facile construction of efficient PCs with TADF characteristics through strategic structural design. These findings serve as a valuable reference for advancing the development of high-performance organic PCs capable of light-induced reversible-deactivation radical polymerization (RDRP).