Extensive experimental and theoretical study suggests that interchromophore electrostatic interactions are among the most severe impediments to the induction and stability of large electro-optic coefficients in electric-field-poled organic materials. In this report, multichromophore-containing dendritic materials have been investigated as a means to minimize unwanted attenuation of nonlinear optical (electro-optic) activity at high chromophore loading. The dendritic molecular architectures employed were designed to provide optimized molecular scaffolding for electric-field-induced molecular reorientation. Design parameters were based upon past experimental results in conjunction with statistical and quantum mechanical modeling. The electro-optic behavior of these materials was evaluated through experimental and theoretical analysis. Experimental data collected from the dendrimer structures depict a reasonably linear relationship between chromophore number density (N) and electro-optic activity (r(33)) demonstrating a deviation from the dipolar frustration that typically limits r(33) in conventional chromophore/polymer composite materials. The observed linear dependence holds at higher chromophore densities than those that have been found to be practical in systems of organic NLO chromophores dispersed in polymer hosts. Theoretical analysis of these results using Monte Carlo modeling reproduces the experimentally observed trends confirming linear dependence of electro-optic activity on N in the dendrimer materials. These results provide new insight into the ordering behavior of EO dendrimers and demonstrate that the frequently observed asymptotic dependence of electro-optic activity on chromophore number density may be overcome through rational design.

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Four dendritic electro-optic (EO) chromophores were designed, prepared, and evaluated to explore the effects on EO behavior of end-on relative to side-on chromophore attachment geometry as well as differing chromophore-to-dendrimer core tether groups. Composite samples of APC and dendritic chromophores were found to exhibit considerably more thermally stable EO properties as compared to samples of the corresponding isolated chromophore. Side-on type binding geometry was found most thermally stable, requiring larger thermal activation energies to induce dipole randomization. Incorporation of a long, flexible chromophore-core tether group greatly enhanced average EO coefficients of the dendritic systems.