Effects of spacer chain lengths on layered nanostructures assembled with main-chain azobenzene ionenes and polyelectrolytes

With the aim of fabricating internally ordered multilayer assemblies using the layer-by-layer electrostatic deposition method, we have prepared polyelectrolytes called ionenes that contain rigid azobenzene chromophores separated by flexible spacer chains, i.e., poly(((4,4'-bis(6-dimethylammonio)hexyl)oxy)azobenzene bromide), PAZ-B, poly(((4,4'-bis(10-dimethylammonio)decyl)oxy)azobenzene bromide), PAZ-10, and poly(((4,4'-bis(12-dimethylammonio)dodececyl)oxy)azobenzene bromide), PAZ-12. UV/vis spectroscopy of solutions shows that PAZ-10 and PAZ-12 form robust lamellar aggregates that could be successfully transferred onto a solid substrate by forming multilayer assemblies with oppositely charged polyelectrolytes, From FTIR spectra of the resulting multilayer assemblies, the alkyl chains appeared to be highly ordered, especially in the case of longer spacer chain. The thicknesses of the PAZ monolayers measured atomic force microscopy were overall consistent with the theoretical values (2.61 and 3.23 nn) determined by a model calculation, based on the tilt angle measurement of chromophore and the molecular length of the repeat unit of the ionenes.