Quantum theory and experimental studies of absorption spectra and photoisomerization of azobenzene polymers

The microscopic properties of azobenzene chromophores are important for a correct description of optical storage systems based on photoinduced anisotropy in azobenzene polymers. A quantum model of these properties is presented and verified by comparison to experimental absorption spectra for trans and cis isomers of cyano methoxy azobenzene. In addition, the trans --> cis quantum efficiency is measured, and hence the combined experimental and theoretical work allows one to determine the essential molecular properties, including magnitude and anisotropy of the absorption cross section and various components of the polarizability tensor for both trans and cis isomers. It is shown that the trans isomer is almost perfectly anisotropic, whereas the cis isomer is approximately isotropic in the plane containing the central C-N=N-C azobridge. The implications for models of the storage mechanism are discussed.