A theoretical and optical spectroscopic study of the mechanism of a tautomeric transformation in the 7-azaindole dimer and the 7-azaindole complex with a water molecule

Electronic, vibrational, and electronic vibrational spectra of the 7-azaindole dimer, the 7-azaindole complex with a water molecule, and their tautomers are calculated. Transition states are considered based on the analysis of frequencies and shapes of low-frequency vibrations and the Mulliken charge redistribution. The performed quantum chemical calculation of chemical reactions enabled the determination of the structure of transition states and proton transfer conditions. It is shown that in the 7-AzI dimer the proton transfer has a character consistent with the formation of a zwitterionic form. The structure of excited states is calculated and the fluorescence spectra of the first electronic transitions that can be used as a criterion of the formation of 7-AzI tautomers as a result of chemical reactions proceeding through a proton transfer in the 7-azaindole dimer and the 7-azaindole complex with a water molecule, are interpreted.