Influence of intermolecular hydrogen bond interaction on fluorescence mechanism for ESIPT characteristic o-Hydroxybenzaldehyde

Abstract

The excited state intramolecular proton transfer (ESIPT) processes and fluorescence mechanisms of the o-hydroxybenzaldehyde (OHBA) and OHBA-MeOH have been investigated in cyclohexane and methanol solvents, by means of the density functional theory and time-dependent density functional theory. For OHBA, there is not enol form in the first excited state, by analysis of geometric structure and infrared vibrational spectra. The optimized potential energy curve indicates that OHBA can undergo a barrier-free ESIPT process. The molecular dynamics process demonstrates that OHBA has a 502 nm fluorescence. In OHBA-MeOH, the optimized geometric structure shows that OHBA-MeOH has enol form on the first excited state. There is a 0.252 kcal/mol energy barrier in the ESIPT process of OHBA-MeOH, by reason of intermolecular hydrogen bonded interaction. The excited state dynamic process indicates that forward and backward ESIPT reaction both can occur in OHBA-MeOH, the enol and keto forms can emit fluorescence. The calculated fluorescence wavelengths are 362 nm and 439 nm in OHBA-MeOH, respectively. These results indicate that the intermolecular hydrogen bond interaction can cause the energy barrier in the ESIPT potential energy curve, which further influence the fluorescence mechanism of OHBA. Our research work can provide the valuable theoretical reference for the design and application of fluorescent probe field.