The photoisomerization kinetics of azobenzene (Az) chromophores tagged to polystyrene (PS) in thin films, was analyzed. It was observed that absorbance monotonically increased with decreasing wavelength, even though the Az probes were not present in the film. To confirm whether the presence of the surface layer truly accelerates the trans to cis photoisomerization, a 160 nm thick film of PS was put onto the PS-Az film with the thickness of 40 nm. The bilayer's x value decreased to 0.67 ∓ 0.01 because of the interfacial region was composed of the two original surfaces. The results show that surface region dynamically behaves as liquid for the photoinduced trans to cis isomerization of the Az probes.
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