A novel switch on and reversible optical sensor as an efficient, selective receptor for Zn(II) ion and its biological application.

In the present study, a promising optical sensor (TR) was designed, synthesized, characterized and its chemosensing mechanism has been explored through 1H NMR, ESI-MS, UV-Vis absorption and emission spectral studies. This compound exhibits a drastic change in its optical properties when treated with Zn2+, whereas other metal ions do not respond. This provides a naked eye detection for Zn2+ ion. In methanolic medium, Zn2+ ion induces strong fluorescence in TR with large Stokes shifts up to ∼132 nm. A 5-fold increase in fluorescence intensity of TR in presence Zn2+ ion is due to inhibition of ESIPT (Excited State Intramolecular Proton Transfer) and -C=N isomerization with large increase in the ICT (Intramolecular Charge Transfer) character of TR in the excited state. The Job's plot and BH plots reveal the formation of 1: 1 stoichiometry with an estimated binding constant of 3.9 × 107 M-1. The detection limit of TR was found to be 3.85 nM. The TR could be regenerated by adding EDTA solution to the complex formed during interaction. The pH studies indicate that TR could render pH dependent fluorescence measurements in a live physiological environment. Computational technique was used to optimize the structures and the theoretical results are correlated with the experimental results. The possible utilization of TR as bio-imaging fluorescent sensor with 98.57% cell viability to detect Zn2+ in HeLa cells was also explored by fluorescent cell imager.