Atomic Force Microscopy Studies of Photoisomerization of an Azobenzene Derivative on Langmuir-Blodgett Monolayers

Materials which undergo a reversible change in their optical transmission characteristics when irradiated (the photochromics) offer potentially exciting applications for optical data storage or as molecular switching devices. The azobenzenes belong to this family of photochromic materials. They undergo a reversible cis/trans photoisomerization upon UV irradiation in solution. For the incorporation of these materials in functional molecular devices the organic molecules can be deposited on solid substrates as thin films using the Langmuir-Blodgett technique. However, once the organic molecules are incorporated into a rigid matrix, the question arises as to whether the cis/trans isomerization process occurs and, if so, to what extent. Extensive photochemical studies of azobenzene chromophores in polymer solids have addressed the influence of free volume distribution on the extent of trans/cis isomerization. It is also of interest to study the effect of spatial restrictions on the isomerization process in Langmuir-Blodgett films.