Solvatochromic and computational study of ground state and excited state dipole moments of coumarin dyes in polar and non-polar solvent environments

Abstract The solvent effect on the photophysical properties of two coumarin derivatives 4-Hydroxy-3-nitrocoumarin (C1) and 3-(Bromoacetyl)coumarin (C2) is examined using UV-VIS and fluorescence spectroscopic procedure in polar and non-polar solvent environments. Lippert, Bakhshiev and Kawaski-Chamma-Viallet correlations were evoked for the calculation of their excited state dipole moments as well as change in the dipole moment. Meanwhile Reichardt’s microscopic solvent polarity parameter \(\:{E}TN\) is also used for the same. The ground state dipole moment is evaluated using Gaussian 16 program and geometry optimization using DFT method at 6–311 + + G (d, p)/B3LYP. The excited state dipole moments of both the compounds calculated from different equations are found to be higher than that of ground state indicating the intra molecular charge transfer (ICT) and twisted intra molecular charge transfer (TICT) in their emitting singlet states