Rational design of nanofibers and nanorings through complementary hydrogen-bonding interactions of functional pi systems

Abstract

A simple protocol to create nanofibers and -rings through a rational self-assembly approach is described. Whereas the melamine–oligo(p-phenylenevinylene) conjugate 1a self-aggregates to form ill-defined nanostructures, conjugate 1b, which possesses an amide group as an additional interactive site, self-aggregates to form 1D nanofibers that induce gelation of the solvent. AFM and XRD studies have shown that dimerization through the melamine–melamine hydrogen-bonding interaction occurs only for 1b. Upon complexation with 1/3 equivalents of cyanuric acid (CA), conjugate 1a provides well-defined, ring-shaped nanostructures at micromolar concentrations, which open to form fibrous assemblies at submillimolar concentrations and organogels in the millimolar concentration range. Apparently, the enhanced aggregation ability of 1a by CA is a consequence of columnar organization of the resulting discotic complex 1a3·CA. In contrast, coaggregation of 1b with CA does not provide well-defined nanostructures, probably due to the interference of complementary hydrogen-bonding interactions by the amide group.