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.