A fluorescence switch based on a controllable photochromic naphthopyran group

► Naphthopyran was first used to fabricate fluorescence switch with benzimidazole derivative. ► Fluorescence intensity can be modulated by controlling the UV irradiation time. ► Fluorescence intensity can be adjusted by changing the ratio of benzimidazole derivative to naphthopyran. ► Decrease of fluorescence intensity is attributed to the interaction of benzimidazole derivative and naphthopyran.