Excited-State Geometries of Heteroaromatic Compounds: A Comparative TD-DFT and SAC-CI Study.

The structures of low-lying singlet excited states of nine π-conjugated heteroaromatic compounds have been investigated by the symmetry-adapted cluster-configuration interaction (SAC-CI) method and the time-dependent density functional theory (TDDFT) using the PBE0 functional (TD-PBE0).In particular, the geometry relaxation in some ππ* and nπ* excited states of furan, pyrrole, pyridine, p-benzoquinone, uracil, adenine, 9,10-anthraquinone, coumarin, and 1,8-naphthalimide as well as the corresponding vertical transitions, including Rydberg excited states, have been analyzed in detail. The basis set and functional dependence of the results was also examined. The SAC-CI and TD-PBE0 calculations showed reasonable agreement in both transition energies and excited-state equilibrium structures for these heteroaromatic compounds.