Supramolecular nanostructures formed from dicationic azobenzene compounds and perfluorinated dicarboxylic acids

A new family of supramolecular nano-assemblies is obtained from p.p' -bis-(ω-dipyridyl decylamido)-azobenzene bromide (1) and perfluorinated dicarboxylic acid (HOOC-(CF₂)_n-COOH: n=5; 2, n=6; 3, n=7; 4, n=8; 5). Their aggregation characteristics are studied by UVVis spectroscopy, dynamic light scattering (DLS), FT-IR spectroscopy, transmission electron microscopy (TEM) and atomic force microscopy (AFM). The FT-IR spectra of 1-4 in the solid state exhibit v_c=_o, V_OH, and the Fermi resonance peaks at 1685, 2500, and 1900 cm^-1, respectively. The observed spectral change indicates that 1-4 is complexed by hydrogen bonds formed between the pyridyl and carboxyl groups. When 1-2 and 1-4 are dispersed in CHCl₃/CH₃OH (39/1 by volume), globular aggregates with the average diameter of 700 ∼ 1000 nm (1-2) and 300 ∼ 800 nm (1-4) are observed by TEM. Consistently, spherical aggregates (diameter: ca. 800 nm (1-2), ca. 400 nm (1-4) are observed in solution by DLS. Such aggregate structures are not, however, observed for 1-3, 1-5 complexes. Interestingly, nano-ring structures are obtained by dropping CHCl₃/CH₃OH (39/1 by volume) solution of 1-4 on HOPG. The present supramolecular system provides a novel means to construct molecular patterns which are self-assembled from bifunctional hydrocarbon and perfluorinated subunits.