A novel turn-on red light emitting chromofluorogenic hydrazone based fluoride sensor: Spectroscopy and DFT studies

Abstract

A new simple, small molecule hydrazone was synthesized from 1:1 condensation reaction of anthrone and 2-hydrazinobenzoic acid. It was characterized by absorption, emission spectrometry, FTIR, NMR, mass studies and investigated as a ratiometric, turn-on, luminescent chemosensor of fluoride ion (F−) in the red region (550−700 nm). The sensor is highly selective for fluoride ion in the DMSO medium in presence of other anions (Cl−, Br−, I−, PO43−, CN−, AcO−) with the limit of detection of ∼10−5 M. Upon addition of fluoride this chromofluorogenic sensor showed an instant color change from pale orange to red which was observed in naked eye and emitted red fluorescence under the UV light. A huge red shift of the ligand was observed in presence of F− which is of great interest. The energy optimized structure, electronic transitions involved in absorption and emission spectroscopy were supported by DFT and TDDFT studies. This color change was captured in RGB grabber application, installed in a smart phone which might be applicable for monitoring fluoride ion concentration in non-aqueous environment. In addition the sensor was used for the detection and estimation of F− in real samples using UV–vis spectroscopy. The results obtained were close to values obtained from the fluoride meter. Thus the above sensor might be used for the analysis of fluoride for real applications.