Freezing out all-optical poling dynamics of azophenylcarbazole molecules in polycarbonate.

In this work we have extended the application of a theoretical model describing the processes of all-optical poling of isomerizable molecules while taking into consideration the thermoisomerization related findings presented in the literature. A model describing all-optical poling transients using a three relaxation rate approach was contrasted with the experimental results of azophenylcarbazole doped polycarbonate measured in a wide range of temperatures from 150 to 300 K, thus covering the β transition for the host. By means of a long timescale and low temperature, we were able to better resolve the thermoisomerization and orientational diffusion processes. The cis → trans thermoisomerization relaxation rates k1 and k2 were obtained in the range 10−5 to 10−2 s−1 and the relaxation rate k3 of the orientational diffusion of the trans isomer in the range 10−6 to 10−4 s−1. The rates exhibited diverse temperature dependent behaviors: the two lowest (k2,k3) manifested Arrhenius type dependencies (Ek2 = 157 meV), whereas, the highest (k1) showed a temperature dependence that is non-Arrhenius, or undistinguished for our experimental conditions. The latter was interpreted using the geometrical “adjustment” model. By investigating chromophore–polymer systems at temperatures far below Tg, we were able to uncover the situation when the cis → trans transition is switched-off and the orientational randomization is suppressed. Thus, we could consider the chromophores as “frozen”.