Theoretical model of photoinduced anisotropy in liquid-crystalline azobenzene side-chain polyesters

A theoretical framework for the temporal behavior of photoinduced anisotropy in liquid-crystalline azobenzene side-chain polyesters is constructed. The domain structure of the material is taken into account and intermolecular interactions are included through a mean-field description. Photoinduced $\mathit{trans}\leftrightarrow \mathit{cis}$ isomerization is taken as the dominating source of chromophore reorientation events, and it is demonstrated how this mechanism in conjunction with the multidomain picture is able to account for the long-term stability of the anisotropy. The photoinduced birefringence is calculated by means of a truncated basis method, and in addition the photostationary solution is obtained. Comparison between theory and experiment shows excellent agreement in the entire range of intensities used experimentally.