Structure and electronic spectral property of coumarin–chalcone hybrids: A comparative study using conventional and long-range corrected hybrid functionals

The structures and electronic absorption spectra of a series of coumarin–chalcone hybrids have been investigated with density functional theory (DFT) and time-dependent density functional theory (TDDFT). Standard hybrid (PBE1PBE and BHHLYP), hybrid meta (BMK, M06, M06-2X and M06-HF) and long-range corrected hybrid (CAM-B3LYP) functionals have been chosen for calculations. The relative performance of the seven exchange–correlation functionals has been discussed and it turns out that, within the selected TDDFT framework, BMK emerges as the most efficient hybrid functional for coumarin–chalcone hybrids with a mean absolute error (MAE) of 0.16 eV (21.0 nm). Based on BMK results, the structure-spectra relationship and the effects of substituent, solvent and elongation of the conjugate chain on electronic spectra have been discussed. The experimentally observed substitution and solvent effects are well reproduced by calculation. The results reveal that the lowest energy transitions should be of intramolecular charge transfer (ICT) nature, which predominantly correspond to the π → π* transitions from HOMO to LUMO.