Photochromism of dihydroindolizines: Part VIII. First holographic image recording based on di- and tetrahydroindolizines photochromes

The photochromic compounds dihydroindolizine (DHI) and tetrahydroindolizines (THIs) containing dicyano and diesters were prepared via nucleophilic addition of the corresponding heterocyclic bases to spirocyclopropenes. These compounds showed good photochromic reactions both in solution and in polymethylmethacrylate (PMMA)-matrix by photo-irradiation. Holographic recording was measured by employing the thin films of PMMA-DHI and PMMA-THI as recording media. The PMMA-films of DHIs 1–3 were studied with regard to their photochemical switching potential of holograms. In the PMMA-film, these coherent beams were interfering to create a holographic pattern, showing equidistant bright and dark lines. Laser light at 532 nm induced the bleaching processes 1a → 1 and 2a, 3a → 2, 3 thus writing the pattern as sinusoidal modulated interference intensity in the photochromic material. The photochemical burning of the interference pattern by the processes 2 → 1a and 2a, 3a → 2, 3 is generating the negative holographic pattern in the form of 1 or 3. The positive recording technique showed that 1-PMMA produce a hologram grating employing a λ > 400 nm laser beam with only 1 mW/cm2 intensity. This was sufficient to generate a holographic grating due to the high-forward quantum yield for 1 → 1a of 0.8. The present results indicate that, the UV-laser generated holograms are produced with lower light intensities compared to the vis-laser process in the negative technique. The recording of volume holograms was achieved on the basis of data and information recording system.