Investigation of the structures and electronic spectra for coumarin 6 through TD-DFT calculations including PCM solvation

Coumarins are well-known laser dyes in the blue-green region and studies on their electronic spectroscopy are important for understanding of their solvatochromic properties. A theoretical research of the various properties of the ground (S0) and first excited states (S1) of coumarin 6 in different solvents, including absorption and emission spectra, is presented here. Four isomers of coumarin 6 are investigated and compared. The excited-state geometries were optimized at the CIS level of theory whereas for the ground state, the HF and B3LYP levels of theory were applied. The geometric relaxation between the S0 and S1 states was examined and explained in terms of the nodal patterns of the highest occupied and lowest unoccupied molecular orbitals. The absorption and emission spectra in various solvents were calculated using the time-dependent density functional theory in combination with the polarized continuum model, and the results are in very good agreement with experimental measurements.