Combination of theoretical calculation and experiment to study the excited state proton transfer behavior of trifluoroacetamidoanthraquinone with different substitution positions

Abstract

The excited state proton transfer behaviors of TFAQ, 1,4-Bis-TFAQ and 1,8-Bis-TFAQ in dichloromethane, acetonitrile and ethanol solvents are studied by combining the experiments and theoretical calculations. A series of analyses including geometric structures, vibrational spectroscopy, uv-vis spectroscopy and fluorescence spectroscopy, AIM theory, frontier molecular orbital theory and potential energy curves proved that TFAQ can undergo proton transfer processes in all three solvents due to the extremely small energy barrier. But for 1,4-Bis-TFAQ, although the energy barrier of the potential energy curve is not high, the normal structure is more stable than the proton-transfer structure in the excited state, so it is difficult to occur the proton transfer process. In particular, 1,8-Bis-TFAQ only exhibits proton transfer behavior in ethanol solvent. We believe that 1,8-Bis-TFAQ and ethanol molecules associate to form a more stable new structure, which causes this phenomenon. In addition, the influence of different substitution positions of trifluoroacetamido on the ESIPT process of TFAQ derivatives can be explained by the nodal pattern of the wave function.