Bis-(2-Hydroxybenzylidene)-1H-Pyrazole 3,5-Dicarbohydrazide as a Novel Chemosensor for the Detection of Endogenous Zinc: A Fluorometric Study

The study reports synthesis and photophysical studies of a new zinc sensing pyrazole scaffold structurally characterized to be bis(2-hydroxybenzylidene)-1H-pyrazole-3,5-dicarbohydrazide (PHSA). Excitation of the probe at 330 nm results in an emission band at 417 nm which ratiometrically red shifts to 466 nm upon Zn²⁺ addition in an unprecedented way. The photo induced electron transfer (PET) coupled intramolecular charge transfer (ICT) working for a dual-channel fluorescence emission pathway is observed and studies were supported with density functional theory and NMR titration experiments. The probe exhibited dissociation constant of 1.2156 and detection limit as low as 992 nM. The cytotoxic effects of the probe on 60 tumour cell lines were tested. The intracellular zinc sensing with reversible binding potential is verified with fluorescence microscopy experiment.