CONICET | Buscador de Institutos y Recursos Humanos

Photoresponsive polymers containing azobenzene chromophores are actively investigated for various applications, including optical data storage, optical switching, and optoelectronics.[1-3] Their optical properties stem from reversible photoisomerization of the azobenzene moiety when excited with linearly polarized light. Azo groups align their dipolar moments perpendicular to the light polarization by cis-trans isomerization cycles. The concentration of the chromophores aligned perpendicular steadily increases, until saturation level is attained. The net result is an anisotropic material. This process is not in a state of thermodynamic equilibrium therefore the alignment would relax to a random configuration in the absence of irradiation. To prevent the randomization of the orientated molecules, the Azo chromophores were usually incorporated in a polymer which has a high glass transition temperature (Tg). Other attempts to improve chromophore loading and alignment stability were: covalent attachment of the chromophore to the polymer as either pendant group or a comonomer, or crosslinking the active moiety into the polymer system. It is conceivable besides, that the loss of anisotropic ordering could be suppressed by a confinement effect. It would be interesting to know how azobenzene polymers behave in a confined geometry with reference to the photoalignment property. Such a confining environment may be provided by self-organized nanodomains in diblock copolymers (DBC). If the guest is confined within a specific domain of a microstructured DBC due to immiscibility in the surrounding block component, the microstructure may further frustrate any reorientation and aggregation of the chromophore. We have investigated the growth and decay processes of the optically induced birefringence in Azo containing films of polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA).