Photoinduced anisotropy in a family of amorphous azobenzene polyesters for optical storage

We investigate parameters associated with optical data storage in a variety of amorphous side-chain azobenzene-containing polyesters denoted as E1aX. The polyesters possess a common cyanosubstituted azobenzene chromophore as a side chain, but differ in their main-chain polyester composition. Seventeen different polymers from the E1aX family divided into four classes, depending on the type of the main-chain substituent (one-, two-, and three-ring aromatic or alicyclic) have been thoroughly investigated. Various parameters characterizing the photoinduced birefringence in these materials, such as the response time, thermal and light stability, and long-term stability under ambient light at room temperature have been measured. Each of these parameters is quantitatively represented and therefore it is possible to make a clear comparison between the properties of the polymers. The results indicate that the long-term stability at ambient temperature is closely related to the thermal stability of the photoinduced birefringence. A strong correlation has also been found between the response time and the stability of the induced anisotropy toward illumination with unpolarized white light. One of the classes of E1aX polymers characterized by two-ring aromatic substituent in the main chain is a good candidate for optical data storage media. A recording energy of approximately 2 J/cm2 is sufficient to induce high refractive-index modulations of Δn=0.13 in these materials, which is retained even at elevated temperatures (>130°C). Long-term stability of greater than one year for the induced anisotropy has also been achieved.