Conjugated\nCross-linked Phenothiazines as Green or\nRed Light Heterogeneous Photocatalysts for Copper-Catalyzed Atom Transfer\nRadical Polymerization

Abstract

Using\nthe power of light to drive controlled radical polymerizations\nhas provided significant advances in synthesis of well-defined polymers.\nPhotoinduced atom transfer radical polymerization (ATRP) systems often\nemploy UV light to regenerate copper activator species to mediate\nthe polymerization. Taking full advantage of long-wavelength visible\nlight for ATRP would require developing appropriate photocatalytic\nsystems that engage in photoinduced electron transfer processes with\nthe ATRP components to generate activating species. Herein, we developed\nconjugated microporous polymers (CMP) as heterogeneous photocatalysts\nto exploit the power of visible light in promoting copper-catalyzed\nATRP. The photocatalyst was designed by cross-linking phenothiazine\n(PTZ) as a photoactive core in the presence of dimethoxybenzene as\na cross-linker via the Friedel–Crafts reaction. The resulting\nPTZ-CMP network showed photoactivity in the visible region due to\nthe extended conjugation throughout the network because of the aromatic\ngroups connecting the PTZ units. Therefore, photoinduced copper-catalyzed\nATRP was performed with CMPs that regenerated activator species under\ngreen or red light irradiation to start the ATRP process. This resulted\nin efficient polymerization of acrylate and methacrylate monomers\nwith high conversion and well-controlled molecular weight. The heterogeneous\nnature of the photocatalyst enabled easy separation and efficient\nreusability in subsequent polymerizations.