Electronegativity effect on the ESIPT process of 4′-N,N-dimethylamino-3-hydroxyflavone (DMA3HF) and its derivatives

4 '-N,N-dimethylamino-3-hydroxyflavone (DMA3HF) has antioxidant activity and excited state proton transfer (ESIPT) property. In this study, the influence of electronegativity on the ESIPT process has been studied by DFT/TD-DFT methods. Except DMA3HF, the substitutes of S and Se have been designed. The analysis of main bond parameters, infrared vibration spectra, and reduced density gradient function shows that the reduction of atomic electronegativity could promote the ESIPT process. Dihedral angle, frontier molecular orbitals and hole-electron analysis indicate that the twisted intramolecular charge transfer (TICT) process has been enhanced by the decreasing electronegativity. The results show that the decrease of atomic electronegativity is beneficial to TICT and ESIPT processess. The effect of O-S-Se electronegativity on ESIPT mechanism was studied. The dihedral angle and hole-electron analysis show that electronegativity effects charge transfer process. The excitation type is determined as n -> pi* transition by using frontier molecular orbitals. The fluorescence reported in the literature comes from the keto form.image