The present invention relates to novel organic dye compounds, and particularly to monomethine cyanine dyes which are sensitive to visible light of a relatively short wavelength.
In a multimedia age, optical recording media such as compact disc recordable (CD-R, a write-once memory using compact disc); and digital versatile disc (DVD-R, a write-once memory using digital video disc), have been highlighted. Optical recording media can be classified roughly into inorganic optical recording media which have recording layers composed of inorganic substances such as tellurium, selenium, rhodium, carbon, or carbon sulfide; and organic optical recording media which have recording layers composed of light absorbents containing organic dye compounds.
Among these optical recording media, organic media are usually prepared by dissolving a polymethine dye in an organic solvent such as 2,2,3,3-tetrafluoro-1-propanol (abbreviated as ITFPII hereinafter), coating the solution onto the surface of a polycarbonate substrate, drying the solution to form a recording layer, and sequentially attaching closely a reflection layer made of a metal such as gold, silver or copper and a protective layer made of an ultraviolet ray hardening resin onto the surface of the recording layer. When compared with inorganic optical recording media, organic optical recording media have the drawback that their recording layers may be easily changed by exposure to light such as reading- and natural light, but have the merit that they can be manufactured at a lower cost because their recording layers can be formed by preparing solutions of light absorbents and directly coating the solutions onto the surface of substrates. Also, organic optical recording media are now becoming the predominant low-cost optical recording media because of the merits that they are mainly composed of organic substances so that they are substantially free of corrosion even when contacted with moisture or sea water; and because information, which is stored in optical recording media in a prescribed format, can be read out using a commercialized reader using thermal deformation type optical recording media, a kind of organic optical recording media.
What is urgently required of organic optical recording media is to increase their recording capacity to suit this multimedia age. The research for such an increment now eagerly continued in this field is to shorten the wavelength of 635-650 nm now used as a writing light to a wavelength of 450 nm or less to increase the recording capacity per one side to a level from 4.7 giga bytes (GB) to 15 GB or higher. The optical recording media with such an increased capacity can record six hours of moving images in quality equivalent to standard TV and just record two hours of moving images in quality equivalent to high-quality TV. However, most of the organic dye compounds now used in optical recording media are not applicable to laser beams with a wavelength of 450 nm or less, and therefore such organic dye compounds could not fulfill the need for high storage density required in many fields.
In view of the foregoing, the object of the present invention is to provide organic dye compounds which are sensitive to visible light having a relatively short wavelength, and to provide uses thereof.
To attain the above object, the present inventors eagerly studied and screened compounds. As a result, they found that specific monomethine cyanine dyes (may be called a xe2x80x9cmonomethine cyanine dyesxe2x80x9d hereinafter), which are obtainable through a step of reacting a quaternary ammonium salt of a nitrogen atom-containing heterocyclic compound having an active methyl group with a quaternary ammonium salt of a nitrogen atom-containing compound having a leaving group, have an absorption maximum in a relatively short-wavelength visible region, and which substantially absorbs visible light in such a visible region. They also found that, among these monomethine cyanine dyes, those which have sensitivity to laser beams with a wavelength of 450 nm or less when in a thin layer form can form minute pits on the recording surfaces at a relatively high density when irradiated by a laser beam at a wavelength 450 nm or less. The present invention was made based on the creation of the novel monomethine organic dye compounds which are sensitive to visible light having a relative short wavelength, and the discovery of their industrially useful characteristics.