A theoretical study of solvent effect on the excited state intramolecular proton transfer of 3‐hydroxyflavone

Abstract

In order to study the effect of solvents polarity on the excited state intramolecular proton transfer (ESIPT) processes of 3‐hydroxyflavone (3HF) in detail, the ESIPT processes of 3HF in toluene, dichloromethane (DCM), and acetonitrile (ACN) were investigated using theoretical methods. The stable configurations of 3HF in ground (S0) and excited (S1) states were optimized. The critical configuration parameters, infrared (IR) vibrational spectra, absorption and fluorescence spectra, frontier molecular orbitals (MOs), charge distribution, and potential energy curves were calculated. The intramolecular hydrogen bonds are obviously enhanced and the electronic density redistributes when excited to S1 state. The strengthening of intramolecular hydrogen bonds and the redistribution of electronic density are beneficial to the ESIPT processes. The analysis of potential energy curves show that the proton transfer processes are feasible in thermodynamics in S1 state, but not in S0 state. In addition, the intramolecular hydrogen bonds gradually weaken when the solvents polarity increases from toluene, DCM to ACN. As the solvents polarity increases, the ESIPT processes are more and more difficult to occur. It can be concluded that the strength of intramolecular hydrogen bonds will be affected by the solvents polarity, and the strength of intramolecular hydrogen bonds are directly related to the difficulty of the ESIPT processes.

Excited State Dynamics of Alizarin Red S Nanoparticles in Solution

“…Surprisingly, the results in Table 1 show a different trend by reducing the lifetime (19 to 14 ps) with nanoparticles instead of extending it (26.5 to 46.8 ps) The dual fluorescence in water indicates a strong competition between ESIPT and fluorescence of the normal form, which is significantly less pronounced in DMSO (see Figures A4 and A5). From theoretical studies it has been concluded that the ESIPT lifetime increases with the polarity of the solvent [38,39]. Another factor may be the aproticity of DMSO.…”