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.
Keywords: colorimetric readout; fluorescein derivatives; interfacial photopolymerization; polymerization-based signal amplification; visible-light-induced photocatalysis.
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