Substituent effect on fluorescence signaling of the naphthalene carbohydrazone based chemosensor: Its implication in the detection of Zn(II) ions and secondary sensing PPi

A series of naphthalene carbohydrazone based fluorescent chemosensors L 1 -L 4 were developed for the detection of Zn 2+ by significant fluorescence enhancement. The binding ratio of the L 1 -Zn 2+ complex was determined by a Job’s plot to be 1:1 and confirmed by ESI–MS studies. The corresponding of the L 1 -Zn 2+ ensemble was elucidated through X-ray crystallography along with spectroscopic studies. Furthermore, the L X -Zn 2+ (X   =   1–2) complexes can specifically detect pyrophosphate (PP i ) in HEPES buffer solution through fluorescence quenching. The detection limit of L X -Zn 2+ (X   =   1–2) for PP i sensing were calculated to be as low as 2.54 ppb and 0.94 ppb, respectively. In addition, due to their good cell membrane permeability and low cytotoxicity, L 1 -L 4 have been applied to sequentially detect Zn 2+ and PP i in living cells. More importantly, the electronic effect of substitute groups on fluorescence signaling have been studied by substituent properties ranging from electron-donating to electron-withdrawing, which sets up a promising strategy for the rational design of fluorescent sensors.