Optimisation of photo-induced geometric isomerisation of azobenzene derivatives in dye-doped polymer films for enhanced photo-induced poling

Photo-induced geometric isomerisation of azobenzene based chromophores can be utilised in a variety of molecular control procedures including photo-induced poling. In such processes additional mobility is imparted to chromophores trapped in a glassy matrix through the photo-induced trans-cis-trans cycle. We show that by using selected narrow wavelength bands of light to induce the isomerisation cycle during photo-induced poling, enhanced levels of polar order can be obtained in comparison to those obtained with monochromatic light. We attribute this to an increase in the fraction of chromophores which undergo isomerisation via an inversion mechanism. As a result, a higher proportion of the chromophores are able to participate in the photo-induced poling process since the free volume for isomerisation is reduced from that required for the rotation mechanism.