Organic Electron Donor–Acceptor Photoredox
Catalysts: Enhanced Catalytic Efficiency toward Controlled Radical
Polymerization
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Abstract
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 (λ<sub>max</sub> = 530 nm, 0.7
mW/cm<sup>2</sup>) and red (λ<sub>max</sub> = 635 nm, 0.7 mW/cm<sup>2</sup>) lights, which exhibited great control over molecular weights,
molecular weight distributions, and end-group functionalities