A detecting Al 3+ ion luminophor 2-(Anthracen-1-yliminomethyl)-phenol: Theoretical investigation on the fluorescence properties and ESIPT mechanism.

2-(Anthracen-1-yliminomethyl)-phenol (AYP) had been synthesized recently and used as a chemosensor to detect Al3+ ion, while its fluorescent properties and excited-state intramolecular proton transfer (ESIPT) process were not investigated in detail. In this study, the molecular absorption and emission spectra were accurately reproduced by using TDDFT/CAM-B3LYP/6-31 + G(d,p) computational method. The ESIPT- chromophore photochemical behaviors and detecting Al3+ ion photophysical changes were explained for the first time at the molecular level. As driving force of ESIPT reaction, the bond parameters and vibrational frequencies of intramolecular hydrogen bond were analyzed by optimizing structures and calculating infrared spectra, analysis of frontier molecular orbitals and reduced density gradient isosurfaces. To further elucidate the proton transfer reactive paths, we scanned the potential energy curves of AYP chemosensor in different electronic states. By comparing potential barriers of the S0 and S1 states, the proton transfer is confirmed to occur in the S1 state. In addition, the experimentally unpresented AYP-Enol fluorescence signal was assigned via analyzing molecular fluorescent properties. Moreover, the calculated fluorescence spectra were employed to explain carefully the mechanism of detection of Al3+ ion.