Multireference Møller-Plesset perturbation theory with complete active space configuration interaction (CASCI-MRMP) is applied to the study of the valence π → π* excited states of all-trans linear polyenes C 2nH 2n+2 (n = 3-14). Our focus was to determine the nature of the four lowest-lying singlet excited states, 21Ag-,11Bu+,11Bu-and31Ag- and their ordering. The ionic 11Bu+ state is the lowest optically allowed excited state, while the covalent 21Ag-,11Bu-and31Ag- states are the optically forbidden states. Theory predicts that the 11Bu- state becomes lower than the 11Bu+ state at n ≥ 7 and that the 31Ag- state also becomes lower than the 11Bu+ state at n ≥ 11.
All Science Journal Classification (ASJC) codes