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 polyel ectrolytes called ionenes that contain rigid azobenzene chromophores separa ted by flexible spacer chains, i.e., poly(((4,4'-bis(6-dimethylammonio)hexy l)oxy)azobenzene bromide), PAZ-B, poly(((4,4'-bis(10-dimethylammonio)decyl) oxy)azobenzene bromide), PAZ-10, and poly(((4,4'-bis(12-dimethylammonio)dod ececyl)oxy)azobenzene bromide), PAZ-12. UV/vis spectroscopy of solutions sh ows that PAZ-10 and PAZ-12 form robust lamellar aggregates that could be su ccessfully transferred onto a solid substrate by forming multilayer assembl ies with oppositely charged polyelectrolytes, From FTIR spectra of the resu lting 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 t he theoretical values (2.61 and 3.23 nn) determined by a model calculation, based on the tilt angle measurement of chromophore and the molecular lengt h of the repeat unit of the ionenes.