Supramolecular assemblies of polyaniline through cooperative bundling by a palladium-complex-appended synthetic cross-linker

A synthetic cross-linker (1) bearing two binding sites for imine moieties in polyaniline has been used to organize polyaniline emeraldine base (EB) or polyaniline emeraldine salt (ES) into aligned assemblies. Complex 1 exhibited highly cooperative binding toward mEB (a repeating unit analogue of EB), for which the association constants K₁ and K₂ were evaluated to be 2.2×10⁴ and 9.4×10⁵M^-1, respectively. ¹H NMR studies revealed that the diimine moieties in mEB are recognized cooperatively in anti-conformation by 1. The ordered structures organized from 1 and EB or ES were efficiently formed through supramolecular bundling. These ordered assemblies have a periodicity of 2.5 nm that was confirmed by means of transmittance electron microscopy (TEM) and high-resolution TEM (HRTEM). The cooperative binding would be important for the bundling and alignment of the polymers, as evidenced by the fact that neither reference compounds 2 nor 3 were capable of producing similar assemblies. The electric conductivity of the samples was measured and the results were discussed.