Microwave assisted synthesis of a novel optical chemosensor for selective Fe3+ detection

Abstract

Recently, there has been significant interest in the design and development of optical chemosensors for recognition of biologically and environmentally important analytes with high selectivity, sensitivity and low detection-limit because of their fundamental role in medical, environmental and biological applications. Herein, a novel fluorogenic signaling probe 6 for the selective detection of ferric ion in mixed aqueous organic media has been developed through microwave assisted Schiff base formation by reacting 4-amino-3-(2-fluorobenzyl)-1H-1,2,4-triazole-5(4H)-thione 5 with thiophene-2-carbaldehyde. The formation of probe 6 was characterized by FT-IR, 1H NMR, 13C NMR, mass spectrometric and single crystal X-ray diffraction analysis. The photophysical results of (Z)-3-(2-fluorobenzyl)-4-[(thiophen-2-ylmethylene) amino]-1H-1,2,4-triazole-5(4H)-thione (6) corroborates its applicability as optical sensing platform for selective Fe3+ detection in pure organic as well as mixed organic-aqueous media. Through fluorescence titration at 478nm, we were confirmed that the ligand 6 exhibited remarkable decline in the fluorescence intensity by complexation between 6 and Fe3+ while it appeared negligible fluorescent quenching in case of the competitive ions in MeOH/water (8:2, v/v, pH 7) at ambient temperature. Meanwhile, the emergence of a new characteristic redshifted signal at 357nm with gradual increment in the absorption intensity on gentle increase in the ferric ion concentration and continuous shifting in the ligand absorption bands after Fe3+ addition ascribed the conformational changes in the ligand structure upon Fe3+ binding. Due to simplicity, low cost, fast response time, considerable sensitivity and robustness, the proposed sensing method might be a practical tool for environmental samples analysis and biological studies.