Erasable holographic storage in azobenzene polyesters and peptides

We describe novel organic compounds based on polyester and peptide backbones with azobenzenes in the side chain for erasable holographic storage. These materials exhibit high diffraction efficiency, high resolution and long storage hfe and can be used for holographic storage in a broad spectral window of 415-530 nm. In polyester thin film systems with a chiral azobenzene, diffraction efficiencies of about 50% have been achieved with just 300 ms exposure. Through atomic force and near-field optical microscopic investigations, we have found an aggregation process encompassing both the main and side chains to be responsible for the permanent storage in the case of polyesters. The stored information can be erased globally in this case with heat. On the contrary, holograms written in peptide films are not totally erased even after exposure to 250 degrees C for one month. However, the information can be locally erased using circularly polarized light. A strong polarization dependent surface relief is observed both for the polyesters and peptides. Through FTIR and surface profile measurements, we further show that irradiation of the films with p-polarized light results in a large surface roughness. We show that in the case of the polyesters the storage is mostly due to optical anisotropy and in the case of the peptide oligomers, both the anisotropy and surface relief are large.