Ab initio modeling of excited state absorption of polyenes

Vertical excitation energies and transition dipole moments between excited electronic states have been calculated for the trans-polyenes series C4H6-C12H14 in order to study the formation of excited state absorption spectra of these species. Quadratic response theory is applied in conjunction with the self-consistent field method and a hierarchical set of coupled-cluster methods. The convergence of the excited state absorption, with respect to wavefunction and treatment of electron correlation and also the length of the oligomer unit, is studied, revealing a considerable demand on the computational effort in order to predict the excited state spectra with precision. The organization of the excited states is found to change in character along the polyene series. The inflexion point for the vertical excitation energies between the one-photon allowed 1(1)B(u) and the two-photon 2(1)A(g) state is predicted to occur between hexatriene and octatetraene. Good agreement with experiment is obtained for butadiene and hexatriene for which the most accurate calculations have been carried out.