An isonicotinohydrazide based fluorescence sensor for detection of Zn2+ in biological systems: Experimental and theoretical studies along with cell imagine

•A Zn2+ selective turn-on optical sensor (DIH) with ESIPT process was reported.•DIH showed high selectivity and sensitivity Zn2+ over other metal ions tested.•The detection mechanism was elucidated by ESI–MS, NMR and DFT calculations.•The sensor is suitable for imaging Zn2+ in living cells.