Photoinitiated Free‐Radical Polymerization of 4,5,6,7‐Tetrahalogenated Fluoresceins

Abstract We demonstrated the photoredox catalytic performances of fluorescein derivatives, bearing heavy halogen atoms (Br or I) on a benzoic acid group, using photoinitiated free‐radical polymerization. 4,5,6,7‐Tetrabromofluorescein and 4,5,6,7‐tetraiodofluorescein were used as visible‐light‐photoredox catalysts to initiate polymerization of poly(ethylene glycol) diacrylate and N ‐vinylpyrrolidone in the presence of triethanolamine under aerobic conditions. Their photocatalytic performances were evaluated by the hydrogelation of photopolymerization both on the surface of an agarose film and in a liquid solution. The polymerization degree increased considerably in the following order: tetraiodofluorescein<tetrabromofluorescein<fluorescein. This result was different from fluorescein derivatives containing the heavy halogen atoms on a xanthene core ring. Consequently, the location of the heavy halogen atoms was crucial in the photocatalytic performance of fluorescein derivatives.