Investigation on the mechanism of ESIPT of 2-hydroxy-1-naphthaldehyde-(4-pyridinecarboxylic)-hydrazone and detection of Al3+ ion

Abstract

The sensing mechanism of 2-hydroxy-1-naphthaldehyde-(4-pyridinecarboxylic)-hydrazone for Al3+ is investigated based on the excited-state intramolecular proton transfer (ESIPT) and photo-induced electron transfer (PET) processes. Absorption and fluorescence spectra are calculated, which are consistent with experimental results. By analyzing the major bond parameters, infrared vibrational spectra as well as frontier molecular orbitals, it can be concluded that the hydrogen bond is enhanced in the first singlet excited state (S1), which can also be visualized by the reduced density gradient function. Potential energy curves are also scanned, which can elucidate that the ESIPT process is more likely to occur in the S1 state. Changes in molecular configuration and intensity of fluorescence emission confirmed that the ESIPT and PET processes are forbidden in the presence of Al3+.