Photochromic Optical Memory

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Diarylethenes having heterocyclic rings undergo thermally irreversible and fatigue resistant photochromic reactions. In this research we aimed at developing photochromic optical memory systems using the photochromic diarylethenes. The research was focused to synthesize new diarylethenes, which show photochromism even in the bulk crystalline phase, and to reveal necessary recording conditions for the photochromic memory. We also examined the possibility of photochromic near-field optical recording.Diarylperfluorocyclopentenes having 2,4-dimethyl-, 2,5-dimethyl-, or 2-methyl-5-phenylthiophenes as the aryl groups underwent reversible photochromic reactions in the crystalline phase. The reactivity in the crystalline phase was confirmed by measuring the absorption of the closed-ring forms with a polarizing microscope. A very strong color change by rotating the sample was observed under the polarized light. This is clear evidence of alignment of the colored forms in the crystal. The near-field optical recording using the crystalline photochromic compounds was carried out. Initially the bulk amorphous film (300nm) was irradiated with UV light, and then a small spot was bleached by evanescent light from a small micropipette (100nm). Small marks as small as 80 nm were written in the film. The marks could be erased by irradiation with visible light. This system has 100 times larger memory density compared to current optical memory systems.Non-destructive readout using super-low power laser light and super-resolution using photochromic compounds were also examined. Million times readout using 20 nw laser was performed.