Novel Orientation of Azobenzene Pendant Group in Hybrid Monolayers Composed of Polyimide Langmuir‒Blodgett Film and Alkyl Polysiloxane Self-Assembled Monolayer

A new technique for preparing hybrid monolayers composed of azobenzene pendant type polyimide LB films and self-assembled alkyl polysiloxane monolayers is reported. The hybrid monolayers were prepared by octadecyltrichlorosilane (OTS) adsorption onto the azobenzene containing LB films. Contact angle measurements suggest a stable formation of the hybrid monolayers after the chemical adsorption of OTS molecules onto the LB films. The molecular orientation was determined by FTIR reflection‒adsorption (RA) spectroscopy and second harmonic generation (SHG) technique. In the hybrid monolayers, the molecular orientation of the azobenzene units is sustained by the tightly packed structure of the self-assembled monolayers. The molecular tilt angles relative to the surface normal direction were estimated to be 16° and 39° for the alkyl chain and the azobenzene unit, respectively. Minimal conformational change was observed even after heating the films to 120 °C.