Coumarin Derived "Turn on" Fluorescent Sensor for Selective Detection of Cadmium (II) Ion: Spectroscopic Studies and Validation of Sensing Mechanism by DFT Calculations.

A novel coumarin based Schiff base sensor probe 1, was synthesized and structural elucidation was carried out by FTIR, UV-vis, 1H and 13C NMR and MS spectroscopy. The optical properties of the sensor probe were investigated by employing absorption and fluorescence titrations which showed specific recognition behaviour being highly selective towards Cd2+ over the other 3d transition metal ions. The strong fluorometric response of probe 1 towards Cd2+ ion is attributed to inhibition of C=N isomerization effect upon coordination of the metal ion. The binding stoichiometry was determined by Job's plot and the probable sensing mechanism of the probe towards Cd2+ was investigated by employing FTIR spectra analysis and 1H NMR titration experiments. Computational validation of the sensing mechanism in various modes towards Cd2+ was also performed by carrying out the DFT studies which were found to be in good concordance with the experimental results. The reversible nature of the probe was studied by EDTA titration indicating that it can be reused. Interaction studies of the sensor probe with the BSA showed the practical applicability for the quantitative determination of Cd2+ concentration in the blood plasma. The lower detection limit of the probe upto 0.114 μM further proves its practical application in the sensing phenomenon.