Donor-acceptor polyenes of various lengths, and that combine aromatic electron-donating moieties with powerful heterocyclic electron-withdrawing terminal groups, have been synthesized and characterized as efficient nonlinear optical (NLO) chromophores. Their linear and nonlinear optical properties have been investigated, and variations in these properties have been related to ground-state polarization (dipole p ) and structure. In particular, unprecedented quadratic hyperpolarizabilities (p) have been achieved (up to p(0) =I500 x 10-30esu) by reduction of the bondlength alternation (BLA) in the polyenic chain. In each series of homologous com-

Articles you may be interested inOne-and two-photon absorption in transition metal oxide glasses Measurement and analysis of molecular hyperpolarizability in the two-photon resonance regime Relationship between static vibrational and electronic hyperpolarizabilities of π-conjugated push-pull molecules within the two-state valence-bond charge-transfer modelIn the search of organic molecules with large two-photon absorption cross-sections, the push-pull dipolar and quadrupolar chromophores have both attracted major attention. In order to provide the basis of molecular engineering and comparison of these two families of molecules, we implement multivalence-bond states models based on measurable parameters. The analytical expressions of the resonant two-photon absorption cross-sections are derived for both families of molecules. Difference and likeness in a number of features are outlined by comparing the results obtained for these molecular systems. The multivalence-bond states models provide useful guidelines for the design of push-pull dipolar and quadrupolar chromophores with enhanced two-photon absorption cross-sections.

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