Solvent effects on excited state intramolecular proton transfer mechanism in 4-(N,N-dimethylamino)-3-hydroxyflavone

Lifeng Jia, Fang Wang, Yufang Liu

Index: 10.1016/j.orgel.2018.03.030

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Abstract

The excited state intramolecular proton transfer (ESIPT) dynamics and photophysical properties of 4-(N,N-dimethylamino)-3-hydroxyflavone (DMAF) in acetonitrile (ACN) and ethanol (EtOH) were investigated by density-functional theory (DFT) and time-dependent density-functional theory (TDDFT) methods at B3LYP/6-31G (d,p) level. The calculation results show that hydrogen bond in the first excited state (S1) is strengthened, which can facilitate the process of proton transfer. The absorption and emission spectra obtained through the vertical excitation energies agree well with the experiment, which confirm the rationality of the choice of theoretical methods. In addition, the frontier molecular orbitals (MOs) analysis indicates the intramolecular charge transfer, which can reveal the tendency of ESIPT reaction. In order to explore the mechanism of the ESIPT process, the potential energy curves of the ground state (S0) and the S1 state have been constructed. Based on the energy potential barrier of 3.48 kcal/mol for DMAF molecule and 5.48 kcal/mol for 4-(N,N-dimethylamino)-3-hydroxyflavone/ethanol (DMAF-EtOH) complex in the S1 state, we can find that the proton transfer occurs more easily in acetonitrile solvent.