Determination of ground and excited state dipole moments of amino-benzimidazole by solvatochromic shift methods and theoretical calculations

Solvatochromic behavior of 2-aminobenzimidazole (2-AB) has been studied in different solvents at room temperature. The observation of the bathochromic shift in the absorption and fluorescence spectra of molecules indicates a strong interaction with solvents in the excited state. The difference in the excited-state (μe) and the ground-state (μg) dipole moments has been estimated by using the theory of solvatochromism from Bakhshiev, Bilot-Kawski, and Dimroth-Reichardt equations. Higher values of dipole moment have been observed for excited state compared to the corresponding ground state values indicating an intramolecular charge-transfer (ICT). Then in order to carry out a theoretical investigation, the values of dipole moments were calculated in the gas phase with TDDFT/B3LYP. Based on these results, we propose a solvation model consistent with theoretical and experimental results wherein we showed the specific interactions between solvent molecules and aminobenzimidazole at the excited state.