Highly sensitive fluorescent hydrazone derivatives for sensing of Cu2+ and its application for actual environment detection

Two novel fluorescent probes PF and KF based on hydrazine, coumarin/quinoline and pyrimidine motif were synthesized. Both of them showed great turn-off fluorescence response to Cu2+ in aqueous solution, which was accompanied by a significant change from bright green and blue fluorescence to dark. They possessed satisfactory detection performances to Cu2+ including specific selectivity and anti-interference, low detection limit, fast response and recyclability. In addition, they were successfully used for paper-based indicators that can be easily applied for naked-eye detection of Cu2+ as expected. Probe PF was also successfully used for portable detection of Cu2+ by smartphone sensing platform and in real water samples. DFT calculations and systematic experiment research indicated possible mechanism was that Cu2+ bound to fluorophore molecules through spin–orbit coupling effect, formation of PF/KF + Cu2+ complex led to fluorescence quenching.