Off–on–off luminescent switching of a dye containing imidazo[4, 5-f][1, 10]phenanthroline

A new acid–base fluorescent switch containing both imidazo[4,5-f][1,10]-phenanthroline and triphenylamine groups has been synthesized. Its fluorescence emissions and absorptions can be reversibly changed through protonation/deprotonation of imidazole and amine moiety by controlling the intramolecular charge transfer (ICT) process, leading to off–on–off fluorescent molecular switching.