Photochromic data storage

Photochromic Organic Dyes. Intensive investigations into this category of substances have led to numerous patent appHcations. Copper—phthalocyanine pigments, organic dyes based on cyanine (Ricoh, Pioneer), naphthochinone (Nippon Denki), and ben2othiopyrane (Sony) (123) have been described. They did not lead, however, to any commercial use. Surveys on the possibiUties of optical data storage with photochromic dyes can be found (124,125). 

The practical use of photochromic dyes as memory layers in erasable and rewritable data storage disks fails not only because of their physical limitations (lacking sensitivity, insufficient stabiHty, low number of cycles), but also because the diode lasers required for switching in the visible range (wavelength between 450 and 600 nm) and the uv-range (around 350 nm) are not available. 

The application of nonlinear optical recording techniques for reversible optical data storage based on the excitation of photochromic molecules by two-photon processes also has been described (154). 

FiaaHy, the use of photoreversible change of the circular dichroism for optical data storage is of iaterest. This technique offers an advantage over photochromic materials ia that the data can be read ia a way that does not damage the stored information. These chirooptic data storage devices have been demonstrated with the example of chiral peptides with azobenzene side groups (155). 

Solid films of spiropyrans are important in optical data storage. Thin films of spirobenzopyran (1.0 (tm) have been prepared by vacuum deposition, and its reversible photochromism has been confirmed.39 The J-aggre-... 

Corredor CC, Huang Z, Belfield KD (2006) Two-photon 3D optical data storage via fluorescence modulation of an efficient fluorene dye by a photochromic diarylethene. Adv Mater 18 2910-2914... 

Photochromism Light Ophthalmic lenses, novelty printing, security printing, cosmetics, optical data storage, memories and switches, sensors... 

Polymer-based photochromic systems have been studied extensively and are attractive in terms of practical applications because of their advantages of stability and processability. A number of reviews and articles dealing with various aspects of photochromic polymers and photoactive biomaterials have been published. 68 Chiral photochromic peptides are discussed in Chapter 13, and photochromic liquid crystals and polymers for holographic data storage and nonlinear optics have been reviewed. 69 Specific stereochemical effects in chiral photoresponsive polymers include ... 

The use of photochromic compounds for optical data storage has been proposed. One of the unsolved problems for practical application is the development of techniques that allow nondestructive reading since the optical data are usually read at the same wavelength as that used in the recording process, the data may fade during the reading process. Sisido et al. 101-104 have proposed the use of photochromic... 

Another interesting possible application of photochromic materials is in the construction of new data storage systems for computers. For some time, researchers have been considering the possibility of... 

Photochromic compounds could possibly be used for rewritable optical storage materials. This is one of the reasons for the widespread current interest in photochromies. Hirshberg is the first person who suggested that a photochromic compound could be used as an optical data storage material. Heller et a .3 summarized the basic requirement of photochromic compounds for rewritable optical storage materials. 

M. Irie, Advances in photochromic materials for optical data storage media, Jpn. J Appl. Rhys. 28, Suppl. 3, 215-219(1989). 

M. Irie, Photochromic diarylethenes for optical data storage media, Mol. Cryst. Liq. 227, 263-270 (1993). 

The combination of these features presents photochromic IsoSm films as interesting and diverse media for optical data storage. In Section 5.4, we consider holographic grating recording in copolymer films and related (combined) photorecording techniques. 

Photochromic materials have been developed in order to dramatically increase the memory density. These materials can be used for photon-mode recording, which is based on the photochemical reaction of the medium. In photon-mode recording, light characteristics such as wavelength, polarization, and phase can be multiplexed in data storage and thus can, in a potentially dramatic ways, increase the memory density. 

Toriumi, A., and Kawata, S. Reflection confocal microscope readout system for three-dimensional photochromic optical data storage. Opt. Lett. 23,1924, 1998. 

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