Photoinduced switching in self-assembled multilayers of ionenes and bolaamphiphiles containing azobenzene units

New organized molecular films with photoswitchable properties are described. The films are composed of oppositely charged ionic compounds in alternating sequence, at least one of them bearing azobenzene moieties. Suitable photoswitchable compounds are cationic and anionic bolaamphiphiles containing azobenzene units, and ionene polyions carrying the azobenzene units in the main chain. Multilayer films are prepared upon electrostatic layer-by-layer adsorption of azobenzene derivatives, either as trans (E-) or cis (Z-) isomer, and oppositely charged polyelectrolytes. Adsorption of cis-rich polyions is found to be advantageous over adsorption of the trans-isomer, because up to three times more material is deposited per dipping cycle. Alternate irradiation of the self-assembled films with UV (<370 nm) and visible light (<450 nm) allows to switch between the trans-isomer and the cis-rich photostationary state. In multilayers of the anionic azobenzene bolaamphiphile, the photoreactivity is controlled by the appropriate choice of the polyelectrolyte counterion. The molecular assemblies are useful as a medium for reversible optical storage of information.