Phenolate-thiazole based reversible “turn-on” chemosensor for the selective detection of carbonate anion: X-ray crystallography, DFT/TDFT, and cell study

Abstract

A new phenolate-thiazole derivative (L) has been synthesized and structurally characterized.The chemo-sensing activity of L is detected by the naked eye for the aqueous carbonate anion in the pH range of 4 to 8. The selective ‘turn-on’ fluorescence occurs through the formation of a stable intermediate L∙CO32–(1) following the PET mechanism. The limit of detection (LOD) is found 0.18 µM based on the absorbance-based assay.The quinonoid form of bromophenol unit binds strongly with CO32– through thiazole nitrogen and hydrazinic nitrogen. Further, the selective holding of CO32– anion over other planar tetranuclear anions (e.g., SO32–, NO3–) happens with several intra and intermolecular hydrogen bonds as envisaged by the DFT/TDFT study. The formation mechanism of L∙CO32– is proposed based on experimental and theoretical studies. The biological experiments (MTT and cell imaging)reveal the non-cytotoxicity nature of L and the biocompatible uptake of L mostly in the cytoplasm at physiological pH.