Photoinduced radical polymerization by methyl fluoresceins under visible light and the application to signal amplification of hydrogen peroxide

We investigate visible‒light‒induced radical polymerization initiated by methyl fluorescein and its derivatives (e.g., methyl ether of fluorescein, methyl ether ester of fluorescein, and methyl ester of fluorescein), which act as photoredox catalysts. The structural alterations of fluorescein noticeably affect their photoredox catalytic performance, which increases in the following order: methyl ether of fluorescein < methyl ether ester of fluorescein < methyl ester of fluorescein ≤ fluorescein. Particularly, the methylation on the phenolic hydroxyl group reduces their performance mainly due to the restraint of tautomerization. Based on this systematic investigation, we synthesize methyl ether fluorescein, bearing aryl boronate as an H 2 O 2 −selective photoredox catalyst and use it to amplify the signal of H 2 O 2 through the photoinduced radical polymerization. In the presence of H 2 O 2 , this photoredox catalyst successfully initiates the polymerization of poly(ethylene glycol) diacrylate and N -vinylpyrrolidone, forming a polymeric hydrogel in 1 min under visible‒light irradiation. For the naked-eye detection of H 2 O 2 , 10 μM of the catalyst allows a successful detection of H 2 O 2 down to 20 μM. We envision that our strategy will be highlighted by mechanistic elucidation of photoredox catalysis and synthesis of multifunctional photoredox catalysts. Other benefits include biomedical applications such as colorimetric sensing of a target analyte, cell surface engineering, and cell therapy. An H 2 O 2 -selective switch-on photoredox catalyst extends the applications of photoinduced radical polymerization under visible light. • Methyl fluorescein and its derivatives can be used as photoredox catalysts for visible-light-induced polymerization. • The structural alterations of fluorescein noticeably influenced their photoredox catalytic performance. • Methyl ether fluorescein bearing aryl boronate exhibited as an H 2 O 2 -responsive photoredox catalyst. • The signal of H2O2 was amplified by visible-light-induced polymerization and detected by naked-eye.