Head-to-tail assemblies of dipolar, piperazine-linked chromophores: synthesis, x-ray structure, and dielectric characterization

A dimer and a mixture of oligomers of acceptor-substituted anilines were prepared, either by Knoevenagel condensation of substituted cyanoacetylpiperazines with p-aminobenzaldehydes or by carbonyldiimidazole-promoted coupling of phenylpiperazines with p-aminocyanocinnamic acids. The resulting oligomeric amidopiperazines possess significantly additive molecular moments when in extended conformations and therefore are potentially valuable for the fabrication of polymer films containing electric field oriented chromophores, such as required for second-order nonlinear optics. The dimer is conformationally defined, and x-ray structural analysis of a model compound confirmed the stereochemistry and bond angles at the amide linkage. The enforced extended conformation of the dimer resulted in an enhanced dipole moment relative to the constituent monomers and raises the possibility of further enhancements in extended higher oligomers.