Excited states and optical response of a donor-acceptor substituted polyene: A TD-DFT study

Optical properties of polar push-pull chromophore (diphenylpolyene with donor/acceptor terminal substituents) are studied using hybrid time-dependent density functional theory (TD-DFT). The optical transitions are thoroughly examined. This includes one- and two-photon absorption, and fluorescence, as a function of the underlying density functional, the basis set choice, and the solvent. Calculated excited state properties are found to be strongly dependent on the density functional model used. Hybrid approximations with small fractions of the orbital exchange (e.g. B3LYP) strongly favor zwitterionic-type states with pronounced charge-transfer character. Models with large percentage of orbital exchange (e.g. BHandHLYP) result in neutral-base electronic excitations.