Naphthalenyl appended semicarbazone as “turn on” fluorescent chemosensor for selective recognition of fluoride ion

Abstract

The reaction of 1-isocyanatonaphthalene with hydrazine hydrate in presence of acetone resulted in the formation of napthyl based semicarbazone (1). The compound has been characterized using UV–Visible, FT-IR, NMR, mass spectroscopic and single crystal X-ray diffraction (XRD) tools. The interaction between 1 and fluoride ion has been investigated by means of UV–Visible and fluorescence spectra. The fluoride ion sensing mechanism of 1 has been studied by hybrid density functional theory (DFT) and time dependent DFT (TD-DFT) methods. The added fluoride ion formed intermolecular hydrogen bonds with the protons of N1H1 and N2H2 groups of 1 in the ground state. The N1H1 proton which is closer to naphthalene moiety prefers to bind fluoride anion in the excited state after deprotonation, which lead to excited state proton transfer (ESPT). The fluoride ion sensing process shows a moderate (31.99 kcal/mol) Gibbs free energy. To understand the dynamic features, the transition state (TS) calculation is performed and the change in entropy is found to be −0.6259 kJ/mol, which shows that the sensing process is thermodynamically allowed.