Degenerate Two-Photon Absorption in All-Trans Retinal: Nonlinear Spectrum and Theoretical Calculations

In this work we investigate the degenerate two-photon absorption spectrum of all-trans retinal ill ethanol employing the Z-scan technique with femtosecond pulses, The two-photon absorption (2PA) spectrum presents a monotonous increase as the excitation wavelength approaches the one-photon absorption band and it peak at 790 nm. We attribute the 2PA hand to the mixing of states (1)B(u)+-like and vertical bar S(1)>, which are strongly allowed by one- and two-photon, respectively. We modeled the 2PA spectrum by using the sum-over-states approach and obtained spectroscopic parameters of the electronic transitions to vertical bar S >, vertical bar S(2)> (""(1)Bu(+)""), vertical bar S(3)>, and vertical bar S(4)> singlet-excited states. The results were compared with theoretical predictions of one- and two-photon transition calculations using the response Functions formalism within the density functional theory framework with the aid of the CAM-B3LYP functional.FAPESP (Fundacao de Amparo a Pesquisa do estado de Sao Paulo)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)CNPq (Conselho Nacional de Desenvolvimento Cientifico e Technologico)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES)U.S. Air Force Office of Scientific Research (AFOSR)Air Force Office of Scientific Research (AFOSR) [FA9550-07-1-0374]European CommissionEuropean Commission[MRTN-CT-2006-035859]European UnionEuropean Unio