The Azobenzene Optical Storage Puzzle — Demands on the Polymer Scaffold?

The basic mechanism of optical information storage utilizing the azobenzene photoaddressable moiety will briefly be introduced. A synthetically flexible polyester matrix covalently integrating cyanoazobenzene in regularly spaced side chains is particularly well suited for holographic storage. Notable figures of merits of thin film materials of liquid crystalline polyesters are: response time to laser light in the order of ns, storage capacity of 5000 lines/mm, high permanent (more than eight years) diffraction efficiency in the order of 50% or higher, and erasability. The implications of the nature of the main chain on polyester morphology and on the permanency of the induced anisotropy are discussed. Arguments for the design and methods of preparation of other very different polymer scaffolds supporting the cyanoazobenzene are elucidated. Whereas oligopeptides invariably form amorphous materials, both copolymethacrylates and dendritic or hyperbranched polyesters provide some materials that exhibit liquid crystallinity. However, none of these other scaffolds offer materials that allow long-lasting anisotropy to be laser light induced.