Persistent radical anion of perylene dianhydride: an emerging metal-free photocatalyst for near-infrared photocontrolled RAFT polymerization

Developing a new type of photocatalyst (PC) and catalytic mechanism for near-infrared (NIR) photocontrolled reversible-deactivation radical polymerization (RDRP) system is charming but challenging. Herein, a novel PC of the persistent radical anion (PRA) (possessing the properties of both radical and anion) was developed for NIR photocontrolled reversible addition-fragmentation chain transfer (RAFT) polymerization, enabling successful polymerization while gaining a deep insight into the mechanism of photo-induced electron transfer RAFT (PET-RAFT) polymerization. Different from the conventional and well-accepted reductive quenching (RQ) pathway, in which the radical anion intermediates of PCs (PCs •− ) must be generated in an excited state (ES), here, the PRA (3,4,9,10-perylenetetracarboxylic dianhydride radical anion (PTCDA •− )) could generate conveniently in situ in the ground state (GS) and subsequently serve as highly efficient PC in the NIR region (740–850 nm). The successful implementation of this strategy elucidates the peculiar role played by light and the real way of electron transfer behaviors. In fact, the transfer of a single electron from PRA to chain transfer agent (CTA) and cleavage of the C–S bonds is a process from ES to GS, rather than always from GS (PCs •− ) to GS (CTA) in the RQ pathway as is well known to all. In addition, the excellent spatial-temporal control and powerful penetration ability of the NIR light were also confirmed by this PRA-catalyzed polymerization system.