Selective anion recognition by inhibition of excited state intramolecular proton transfer process via hydrogen bonding interaction and efficient deprotonation: Spectroscopic and theoretical investigation

摘要

Anion (X) recognition fluorescent chemosensor 5-(4-Fluoro-phenyl)-2-hydroxy-nicotinonitrile (FP2HN) having both -NH and -OH groups in its two tautomeric forms has been synthesized and its excited state intramolecular proton transfer (ESIPT) reaction has been investigated by UV-vis, fluorescence. ~1H NMR spectroscopy in combination with computational calculations. The experimental findings show that FP2HN selectively recognizes F~-, AcO~- and H2PO4~- ions through the formation of-N(O)H···X hydrogen bonding (HB) complex. The binding constant obtained by non-linear fit predicts the binding order of F~- >AcO~- >H2PO4~- >Cl~-. The ESIPT process of FP2HN is inhibited either by the fluoride induced deprotonation of acidic proton of FP2HN or by the formation of a strong -N(0)H.;;X intermolecular hydrogen bonding complex. Further insights into the recognition mechanism of the receptor-anion complexes using ab initio calculations have been performed which support the experimental binding affinity order of F~->AcO~->H2PO4~->Cl~-.