title: Molecular modeling of two-photon absorption and third-order nonlinearities of polymethine dyes for all-optical switching.
abstract: Stimulated by a recent experimental report [Hales JM et al. (2010) Science 327:1485-1488], two-photon absorption and third-order optical nonlinearities of selenopyrylium- and bis(dioxaborine)-terminated polymethine dyes (called SE-7C and DOB-9C) used for all-optical switching were investigated theoretically with time-dependent DFT (TD-DFT) and response theory as well as visualized real-space analysis. The calculated results for the first hyperpolarizability and second hyperpolarizability demonstrated that the two molecules both have large third-order optical nonlinearities. Using real-space analysis, we were able to visually determine that in the one-photon absorption (OPA) process, the first singlet excited state of SE-7C and DOB-9C is an intramolecular charge transfer (ICT) excited state with strong absorption, while the second excited state of these dyes (also termed the "ICT state") shows weak absorption. However, in the two-photon absorption (TPA) process, a larger TPA absorption cross-section was predicted for the second excited state. In this paper, we describe the properties of the S2 excited state, incorporating charge transfer and the transition moment, via real-space analysis, which was very important for understanding the TPA characteristics of the S(2) state.
authors.affiliation: College of Science, Northeast Forestry University, Harbin, 150040, People's Republic of China. yuanzuo.li@yahoo.com.cn
authors.forename: Yuanzuo
authors.initials: Y
authors.lastname: Li
authors.forename: Ying
authors.initials: Y
authors.lastname: Shi
authors.forename: Maodu
authors.initials: M
authors.lastname: Chen
authors.forename: Yongqing
authors.initials: Y
authors.lastname: Li
authors.forename: Runzhou
authors.initials: R
authors.lastname: Su
authors.forename: Meiyu
authors.initials: M
authors.lastname: Zhao
authors.forename: Fengcai
authors.initials: F
authors.lastname: Ma
mesh_terms: D000042:Absorption; D004396:Coloring Agents / Q000737:chemistry*; D004583:Electrons; D007211:Indoles / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D017711:Nonlinear Dynamics; D017785:Photons
chemical_list: D004396:Coloring Agents; D007211:Indoles; C098209:VPM chloride