Dynamic monolayer behavior of a photo-responsive azobenzene surfactant

Photo-responsive behavior of an azobenzene surfactant is observed at the ai r-water interface in terms of the surface pressure modulation with 360 and 420 nm wavelength light. The surface pressure response of the monolayer cha nges depends on the degree of compression of the Langmuir monolayer, expres sed in terms of the area per molecule, as well as the light condition durin g the formation of the Langmuir layer. The azobenzene chromophore requires molecular space to undergo photoisomerization, which causes surface pressur e changes at the air-water interface. Closely packed trans molecules do not fully convert to the cis state under 360 nm due to the steric hindrance an d formation of H-aggregates. The bulky cis chromophores do convert to the t rans state. Ultraviolet-visible spectra of Langmuir-Blodgett (LB) films are blue shifted 17 nm relative to the UV-visible spectra for the azobenzene s urfactant in chloroform solutions, indicating formation of H aggregates. La ngmuir-Blodgett films show different molecular conformation depending on th e light wavelength during compression. (C) 2000 Elsevier Science B.V. All r ights reserved.