Organized photochromic azo-polymeric structures: self-assembled and Langmuir—Blodgett—Kuhn layers

Abstract

Self-assembled monolayers (SAMs) of azo-silane molecules exhibit persistent dichroism upon linearly polarized light irradiation. This dichroism could be both written and erased by irradiation with light of an appropriate wavelength. In addition, the sign of this dichroism can be inverted by choosing the appropriate polarization of the irradiating light, thus showing a ‘smart communication’ between the light polarization and the ultra-thin photochromic layers. Langmuir—Blodgett—Kuhn (LBK) multilayer assemblies of ‘hairy rod’ polyglutamates with stiff main chains and flexible side chains containing photochromic azo units exhibit a highly optically anisotropic structure when the azo molecules are in the trans form, and a nearly optically isotropic structure when the azo molecules are in the cis form. The trans ⇔ cis photoisomerization of the azo molecules switches them between a highly oriented trans configuration and a bent cis configuration, thus turning the anisotropy ‘on’ and ‘off’. In contrast to spun-cast polymer films containing azobenzene units, photoselection under polarized light irradiation does not occur in these LBK structures.