Dual-state emission and photochromic properties of spiropyranindoline derivatives bearing an ortho-hydroxyphenylbenzimidazole moiety

Abstract

Spiropyranindoline derivatives bearing an ortho-hydroxyphenylbenzimidazole moiety were synthesised. The spiropyran cyclic isomers possessed dual-state emission properties. Fluorescence exhibiting an anomalous Stokes shift, due to proton transfer in an excited state, was characterised by a high efficiency with quantum yields of 0.2–0.4 both in solution and in solid-state samples. In solution, the spiropyrans manifested a thermally and photochemically reversible coloration with quantum yields reaching 0.66. The unusual dual-state photochromic cycle of the spiropyrans involved an irreversible photo-staining in the solid state followed by thermal bleaching in solution. The combination of fluorescence and photochromic properties allow spiropyranindoline derivatives bearing an ortho-hydroxyphenylbenzimidazole moiety to be considered as fluorescent molecular switches.