Chemical photostructuration in iodoform-doped carbazolic copolymers for holographic recording

Carbazol-containing polymers were shown to be good reliefographic photosensitive substrates for holographic registration. Holographic images with satisfactory properties were obtained with carbazolic copolymers containing carbazolylethylmethacrylate and octylmethacrylate units and iodoform as sensitizer. The final goal of this study is to find the best copolymer formulation ensuring large amount of data stored with a high transfer rate and an optimized lifetime of the hologram and of the host polymer. It is then crucial to elucidate the involved photochemical mechanisms. We first carried out irradiations at 405 nm (wavelength of the laser diode used for holographic recording) in order to follow the photostructuration of the doped polymer. Spectroscopic analyses showed that the formation of a charge transfer complex is observed and its increase of concentration in the polymer could be followed versus exposure time. We also focused our attention on the durability of the hologram and of the polymeric matrix itself. Under irradiations representative of natural ageing (λ>300 nm), we have shown that the complex is successively formed and destroyed and that the photodegradation of the polymer matrix was also observed.