Solvent effect on the absorption and fluorescence spectra of 7-acetoxy-6-(2,3-dibromopropyl)-4,8-dimethylcoumarin: Determination of ground and excited state dipole moments

The ground state (μg) and excited state (μe) dipole moments of 7-acetoxy-6-(2,3-dibromopropyl)-4,8-dimethylcoumarin (abbreviated as 7ADDC) are estimated from solvatochromic shifts of absorption and fluorescence spectra as a function of the dielectric constant (ε) and refractive index (n). While the ground state dipole moment is determined by using Bilot–Kawski method, the excited state dipole moment is calculated by using Bilot–Kawski, Lippert–Mataga, Bakhshiev, Kawski–Chamma–Viallet and Reichardt correlation methods. Excited state dipole moment is observed as larger than the ground state dipole moment due to substantial π-electron density redistribution. The ground state and excited state dipole moments are observed as parallel to each other with angle of 0°. Solute–solvent interactions are analyzed by means of linear solvation free energy relationships (LSER) using dielectric constant function (f(ε)), refractive index function (f(n)) and Kamlet–Taft parameters (α and β). Atomic charges, electron densities and molecular orbitals are calculated in vacuum and with solvent effect by using both DFT and TDDFT methods. Solvent accessible surface, molecular electrostatic potential (MEP) and electrostatic potential (ESP) are visualized as a result of DFT calculations.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The excited state dipole moment is estimated from solvatochromic shift methods. ► The results reveal that compound is more polar in the excited state than in the ground state. ► It is observed that shifts in absorption band are controlled by dispersion–polarization forces. ► Fluorescence band shifts is controlled by induction–orientation interactions.