Supramolecular chirality from an achiral azobenzene derivative through the interfacial assembly: Effect of the configuration of azobenzene unit

The Langmuir-Schaefer (LS) films of an achiral azobenzene derivative, 4-octyl-4'-(5-carboxypentamethyleneoxy) azobenzene (C8AzoC5), were fabricated and their optical activities were investigated. It was found that the LS film of the trans-C8AzoC5 showed strong Cotton effect, while that of cis-C8AzoC5 did not. The characterization of the LS films by UV-vis, Fourier transform infrared (FT-IR) spectra, and X-ray diffraction (XRD) revealed that this interesting phenomenon was due to the different packing of the azobenzene unit in the LS film. The planar conjugated trans-azobenzene favored ordered cooperative packing in a helical sense and produced the supramolecular chirality, while the cis-isomer did not due to the bulky twisted configuration.