Fluorescent photoswitching of a naphthopyran-benzimidazole dyad with high-degree fluorescent modulation within poly(methyl methacrylate) matrices

A naphthopyran-bridge-benzimidazole dyad which exhibits both fluorescence and photochromism was synthesized and its fluorescence photoswitching was investigated. Irradiation with UV light induces the isomerization of the naphthopyran component to the corresponding merocyanine. The fluorescence of the dyad was switched reversibly between on and off upon UV irradiation and thermal bleaching of the naphthopyran. Using ultraviolet illumination a pattern was created on a polymethylmethacrylate doped film with the dyad. Thus either a non-destructive photoswitch or an image recording system becomes available. The measurement of redox potentials by cyclic voltammetry combined with electronic spectra and a molecular energy diagram of the individual naphthopyran and benzimidazole demonstrated that the transformation of naphthopyran induced energy and electron transfer from the fluorescent benzimidazole to the photochromic naphthopyran, a feature which was also supported by our DFT calculations.