Intermolecular Coupling Enhancement of the Molecular Hyperpolarizability in Multi-chromophoric Dipolar Dendrons
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azobenzene or nitro-azobenzene, having a π-electronic structure coupled with electron donor and acceptor groups (Figure1). Since the electron withdrawing effect of the carboxyl group was weak, a nitro group was introduced to the azobenzene at an ortho position to optimize the second order susceptibility of the chromophore. Calculated electronic properties and molecular hyperpolarizability for these chromophores were summarized in Table I. Azobenzene dendrons were synthesized in a manner similar to those previously described [4], consisting of three distinct chemical unit: the main NLO functional unit, the aliphatic functionality at the end of the dendritic chain (hexadecanoic acid), and the focal unit (a methoxyethoxymethyl group) (Figure 2). The dendritic structure could be built up through a number of generation from one to four, G1-G4. Size exclusion chromatography showed that they had a high purity and a narrow monodispersity in their molecular weights (Mw/Mn/=4.5-4.9 for all dendrons, which agree with polarization showed ratios of / spreading branches. In other researches, it has been shown that the
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