Reversible Photochemical Strain in Langmuir Monolayers

This paper reports investigation of the photoinduced mechanical response of a mono-layer consisting of the copolymer poly(methyl methacrylate)-spiropyran (molecular weight 215 000, 5.1 mole% spiropyran) at an air-water interface. Irradiation with uv-light pulses isomerizes the spiropyran chromophore and leads to a relative surface-pressure increase up to 10% at saturation. The photoexcited state has a typical decay time constant of 20 min. Irradiation with visible light returns the chromophore to the initial state making the mechanical process fully reversible.