Rationally designed novel phenazine based chemosensor with real time Hg2+ sensing application

Abstract

Phenazine derivatives have been explored in the selective detection of ions due to their binding ability with analytes. In this context, C-6 sulfenylated benzo[a]phenazine-5-ols (3a-d)have been synthesied and explored in sensing application. Initially, the molecules were designed by utilizing benzo[a]phenazin-5-ol as a core structure variably substituted with electronically diverse aryl thiols to investigate the substituent effect on their electrostatic properties. The ground state geometry of all the designed molecules was optimized with DFT using B3LYP/6-311G+(d,p) level of theory. Energy gap between FMOs was observed to be minimum and maximum for electron rich and deficient frameworks, respectively. The LUMO electron density in all the designed molecules except for compound bearing nitro group (3c) lies on the phenazine unit. This exceptional behavior enthusiased us to explore their photophysical properties. The compounds were synthesized and characterized using FT-IR, NMR and mass spectrometric techniques. In an attempt to examine their spectral behavior in different solvents, their absorption and emission spectra were recorded. The compounds exhibited absorptions maxima ranging between 475-514 nm, which shifted to longer wavelength while changing solvent polarity from CHCl3 to DMSO thus depicting positive solvatochromism. Similarly, the emission maxima was observed in a range of 570–685 nm with a maximum stokes shift of 6454 cm−1 for 3c. The compound 3c was further explored in the sensing application using DMSO:Water (60:40, v/v) mixture. A blue shift of 30 nm with nearly 7 fold increase in the emission intensity was observed upon addition of Hg2+ into 3c solution. Moreover, LOD of 21.9 nM and binding stoichiometry of 2:1 as determined by Benesi–Hildebrand and Job's plot establish the robust response of developed probe towards Hg2+ ion. The mechanism of complex formation was predicted by 1H NMR titration and DFT studies. Finally, the developed probe has been successfully utilized for sensing Hg2+ in real water samples.