High contrast off–on fluorescence photo-switching via copper ion recognition, trans–cis isomerization and ring closure of a thiosemicarbazide Schiff base

An easily available triphenylamine–isophorone-based Schiff base was synthesized and its specifically triple-addressable molecular photo-switching behaviour via copper ion recognition, trans–cis isomerization and ring closure were investigated in detail. Firstly, compound Lo was able to real-time monitor Cu2+ in an acetonitrile solution via displaying the “turn-on” emission in the near infrared region with high selectivity, and sensitivity. Furthermore, two independently photochromic phenomena based on the distinct mechanisms were found surprisingly, one through the ring closure of the thiosemicarbazide moiety based on a Michael addition reaction in tetrahydrofuran solution and another through the trans–cis isomerization of aldimine (–CN–) in the solid state under the stimuli of UV/visible light. Finally, fluorescence imaging experiments in living cells demonstrated the potential practical applications in biological systems.