Recognition of Mn2+ Ion by Azine Based Fluorescent Chemo Sensor and Its Theoretical Investigation

A different series of oligomeric ester was synthesized by combining different acid chlorides with a novel azine monomer and their structure was confirmed using a variety of spectroscopy techniques. The sensing ability of the synthesized azine fluorophore with various metal ions was evaluated in DMF/H2O solution and it was exposed those fluorophores have selective “turn off” fluorescence reaction to Mn2+ ion. The correlation coefficient was determined using Stern-Volmer linear plot and found to be R2 = 0.99223 for PBHMM and R2 = 0.9517, 0.9526, and 0.9295 for PBHMP, PBHOP, and PBHAP, respectively. The Benesi–Hildebrand plots were used to determine the binding constant of fluorophores Ka and the values are 1.00393, 1.00192, 1.00436, and 1.00132 M–1 for PBHMM, PBHMP, PBHOP, and PBHAP respectively. UV and theoretical (DFT) studies were used to confirm the mechanism of interaction between fluorophore and quencher in the ground and excited states. The monomer and dimer of oligomers were theoretically investigated using DFT at the B3LYP/6-311G level of the fundamental set and is helping to explain the mechanism of the fluorophore interaction with metal ion and electrical studies of the oligomer. In comparison with non-doped oligomers, doped oligomers exhibit increased conductivity upon increasing the iodine doping duration on oligomers. The electrical conductivity of oligomers was compared with charge density on imine nitrogen obtained from Huckel’s equations and band gap values. Dielectric analysis was carried out at different temperatures and frequencies using the four-point probe technique. The PBHAP oligomer shows a high dielectric constant at the low applied frequency at 373 K due to polarized high loosely attached π bonds.