Characterization and structure of side-on azo copolymers in Langmuir-Blodgett films

Three different azobenzene derivatives, namely, 2-(6-methacryloxyhexyloxy)-4-hexyloxy-4′-hexyloxyazobenzene (A1) and poly{6-[5-hexyloxy-2-(4-hexyloxypheny)azophenyloxy]hexyl methacrylate}_x-co-{2-hydroxyethyl methacrylate}_y, (A2, x = 0.8, y = 0.2), and (A3, x = 0.2. y = 0.8), have been synthesized to study the characterization of Langmuir monolayers at the air-water interface and the aggregation and orientation of Langmuir-Blodgett (LB) films on a solid substrate. The surface pressure-area isotherms showed that they could form well-defined condensed-type monolayers, with A1 and A2 undergoing conformational transition. The monolayers of A1 and A3 could be deposited onto substrate at 20 mN/m at 20 °C with a near unity transfer ratio. The polarized Fourier transform infrared and polarized UV-vis spectra revealed that LB films of A1 and A3 on substrates had in-plane orientation with the long axis of azobenzene moiety exhibiting a large tilt angle (42° and 35°, respectively) with respect to the substrate normal. The UV-vis spectra of A1 and A3 gave us information that A1 and A3 formed J-aggregate both in solution and in LB films.