Synthesis of Thermally Irreversible Photochromic Compounds and Their Application for Optical Data Storage Media

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Photochromic compounds are characterized by exhibiting two different chemical forms. A reversible transformation from one to the other is induced by irradiation with light of an appropriate wavelength. The instant image forming property without processing has led to the consideration of their use in rewritable direct read after systems. The requirements for the reversible optical data storage media are followings. (1) Archival storage capability. (2) Low fatigue (can be cycled many times without any significant loss of performance). (3) Sensitivity at diode laser wavelength. (4) Non-destructive read out capability. The present study aimed at development of photohromic compounds which fulfill the above requirements. This was carried out by chemical modification of diarylethenes with heterocyclic rings.In order to gain access to compounds which have sensitivity at longer wavelengths, symmetric diarylethenes with various heterocyclic rings, such as benzothiophene, selenophene, or indole r … More ing, were synthesized. Although diindolylmaleic anhydride shifted the absorption maximum of the closed-ring form to 620 nm, the closed-form was thermally unstable. In an attempt to get thermally stable compounds having the absorption bands at longer wavelengths, unsymmetrically substituted non-symmetric diarylethenes were synthesized. Non-symmetric maleic anhydride with indole ring on one end a thiophene ring on the other end became thermally stable and the absorption maximum of the closed-ring form was observed at 595 nm. The absorption maximum was further shifted to 680 nm by introducing a methoxy group at 5 position of the indole ring and a cyano group at 5 position of the thiophene ring. The non-symmetric compounds showed fatigue resistant property. The intensity of the closed-ring form of non-symmetric maleic anhydride with an indole ring on one end and a benzothiophene ring on the other end remained almost constant even after 1.1 x 10^4 ring-closure/ring-opening cycles. The next problem to be solved is to design compounds which have non-destructive read out capability. Less