Electric-field induced birefringence in azobenzene thin films

It has been recently shown that solar light is able to induce a small birefringence in azo-benzene chromophore containing thin films, parallel to its surface. In order to enhance this effect, towards the development of energy harvesting devices, poly (1-(4-(3-carboxy-4-hydroxy-phenylazo)benzenesulfonamido)-1,2-ethanediyl, sodium salt) (PAZO) cast films were thermally polarized to achieve a net dipole moment in the medium. Therefore, creation and relaxation kinetics curves of PAZO cast films were obtained in terms of poling at different temperatures and applied voltages. Results show that the maximum birefringence induced is proportional to both temperature and applied external electrical field while the relaxation curves reveal that the residual birefringence increases with the temperature, behaviour which is indicative of cooperative orientation processes between the chromophores which in turn guarantees the stability of chromophores orientation.