Photochromic Behaviour of Nano-Structurable Azo-Polysiloxanes with Potential Application in Biology

The miniaturization process involved in the devices of the future industry will require the use of functional molecules capable to response to external stimuli at nanoscale and to integrate into complex architectures. Nanotechnology has a significant impact in drug delivery, genomics, bioengineering, energy storage, electronics etc. The azobenzene-based polymers are one of the most interesting classes of external stimuli sensitive materials due to azo- chromophores trans-cis reversible photoisomerization capacity. This work presents a study of the photochromic behavior of a siloxanic main-chain polymer containing different azo-benzene groups in the side-chain and the correlations with the surface properties modification, using the contact angle method. As a function of the azobenzenic group dipole-moment value and substitution degree, the contact angle method is capable, or not, to evidence the surface properties modifications. The capacity to generate nano-structured surfaces in the case of azo-polysiloxanic films was demonstrated. The polymer chemical structure and the UV irradiation conditions allow controlling the relief topology. As an additional investigation method, molecular modeling studies were effectuated, in order to calculate the azobenzenic groups' dipole- moment values and the supramolecular organization at the film surface.