Synthesis DFT/TD-DFT theoretical studies and experimental solvatochromic shift methods on determination of ground and excited state dipole moments of 3-(2-hydroxybenzoyl) coumarins

Abstract

Solvatochromic behaviour of two 3-(2-hydroxybenzoyl) coumarins 3 and 4 has been studied in different solvents at room temperature. Both derivatives show emission at 371 nm and 422 nm with large Stokes shift of 45 and 74 nm, respectively. Higher values of dipole moment have been observed for excited state compared to the corresponding ground state values, indicating an intramolecular charge-transfer (ICT). The electronic structural and spectroscopic properties of 3 and 4 in gas and in different solvents were calculated by the conductor-like polarizable continuum model (CPCM) and have been investigated by DFT/TD-DFT calculations to account for solute-solvent interaction. Excitation energies and oscillator strengths were calculated and HOMO-LUMO levels have been investigated in gas and solvent phases. The comparison of the atomic charge distributions in the ground and excited states of both 3a and 4a rotamers implies also the intramolecular charge transfer (ICT) process during the excitation period.