Organic Electron Donor–Acceptor Photoredox Catalysts: Enhanced Catalytic Efficiency toward Controlled Radical Polymerization

In this study, we designed and synthesized novel organic single electron donor–acceptor molecules containing a free base porphyrin and a thiocarbonylthio group. The porphyrin acts as a light-harvesting antenna and donates an excited electron upon light irradiation to the electron-accepting thiocarbonylthio group. The excited electronic state of the donor–acceptor generates a radical from the thiocarbonylthio compound to activate a living radical polymerization in the presence of monomers. Thus, these donor–acceptor systems play the roles of highly efficient photoredox catalysts and radical initiators. The presence of both donor and acceptor in a single molecule enhanced the electron transfer efficiency in comparison to the donor/acceptor mixture and consequently greatly increased polymerization rates of vinyl monomers under visible light irradiation. The polymerizations mediated by these electron donor–acceptor photoredox catalysts were investigated under green (λmax = 530 nm, 0.7 mW/cm2) and red (λmax = 635 nm, 0.7 mW/cm2) lights, which exhibited great control over molecular weights, molecular weight distributions, and end-group functionalities.