Investigation of charge-separation/change in dipole moment of 7-azaindole: Quantitative measurement using solvatochromic shifts and computational approaches

Solvatochromic and computational approaches were applied to 7-azaindole (7-AI). The vertical transitions together with the bright singlet states and HOMO-LUMO were obtained from the DFT/TDDFT quantum chemical calculations. The ground and excited electronic states dipole moments hence the change in the dipole moment were investigated by measuring the steady-state absorption and fluorescence spectra in various solvents and by using DFT/TDDFT calculations. The dipole moment in the photo-excited state is significantly larger than the ground state, as obtained both experimentally and theoretically. The higher values of excited state dipole moment than the ground state dipole moment demonstrating a significant charge separation in the photo-excited state of 7-AI, which in turn depends on the solvent polarity and hydrogen bonding ability. Also, the nearly linear relation observed between the fluorescence maximum/Stokes shift and solvent polarity indicates sensing ability of 7-AI towards organic solvents. The present study is important for understanding charge transfer/proton transfer mechanism of DNA base pairs.