Light and Acid-Base Dual-Regulated Atom Transfer Radical Polymerization With ppb Concentrations of Zwitterionic...

Here, we introduce highly efficient, and acid/base-responsive zwitterionic photocatalysts (PC) for photoinduced atom transfer radical polymerization (photoATRP). The electron-withdrawing methylpyridinium substituent enhances the acidity of benzimidazole/naphthoimidazole, enabling the formation of potent electron-donating benzimidazolate anion/naphthoimidazolate anion under weakly alkaline or even neutral conditions. The PCs exhibit visible light absorption and highly reducing excited states. Their fluorescence is quenched by the ATRP initiator with exceptional rate constants of k_q > 10⁹ M^-1 s^-1, more than one order of magnitude higher than those of traditional PCs. At PC concentrations as low as 100 parts per billion (ppb), photoATRP of acrylates exhibits high initiation efficiency and excellent control over molecular weights and dispersity (Đ < 1.1). Notably, the protonation of the PCs in acidic environments leads to the loss of photocatalytic activity and visible-light absorption. Strict temporal control over polymer-chain propagation is achieved through light on-off switching combined with the weak base and acid stimuli. To our knowledge, this is the first demonstration of dual-regulated polymerization using ppb-level of PC concentrations.