The geometries, absorption and fluorescence wavelengths of solvated fluorescent coumarins: A CIS and TD-DFT comparative study

We compare the CIS and TD-DFT excited-state structures of several hydroxy coumarin dyes. These calculations have been performed in both gas-phase and water. In addition, the transition energies corresponding to absorption and fluorescence phenomena have been determined within several theoretical approximations. Though the CIS transition energies are strongly overestimated, this scheme reproduces the major chemical features. However, the symmetry of the excited-state geometries and the solvatochromic effects are not always consistently reproduced by CIS.