Benzobisazole compound and optical recording medium containing the compound

#The present invention relates to a benzobisazole-based compound which is useful as a dye, pigment, photoelectric function material and recording/memory material, particularly as a recording dye for a high-capacity recordable optical recording medium which can be written information therein and read therefrom by means of a blue laser beam. Further, the present invention relates to an optical recording medium containing the benzobisazole-based compound as a recording material, particularly a recordable optical recording medium which can be written information therein and read therefrom by means of a blue laser beam.

#A CD-R (CD-Recordable) is widely used as a recordable optical recording medium that is adapted to specifications of a compact disk (to be abbreviated as “CD” hereinafter). A recording capacity of the CD-R is about 680 MB. Along with a dramatic increase in an amount of information, demand for an information-recording medium with higher density and higher capacity has been increasing.

#Use of laser beams for recording and reproducing which have short wavelengths can make a beam spot small, thereby making high-density optical recording possible. Lately, development of a short-wavelength semiconductor laser to be used in an optical disk system has been proceeding, and red semiconductor lasers for wavelengths of 680 nm, 660 nm, 650 nm and 635 nm are actually currently used (for example, refer to page 65 of Nikkei Electronics No. 592 published on Oct. 11, 1993). A DVD in which over two hours of motion pictures are digital-recorded by use of these semiconductor lasers has actually been used. Since the DVD is a playback-only medium, development of a recordable optical recording medium (DVD-R) corresponding to the capacity of the DVD is also under way.

#FIG. 1 is a cross-sectional structural diagram showing an example of a layer structure of an optical recording medium according to the present invention.

#FIG. 2 is a cross-sectional structural diagram showing an example of a layer structure of an optical recording medium according to the present invention.

#FIG. 3 is a cross-sectional structural diagram showing an example of a layer structure of an optical recording medium according to the present invention.

#The present invention relates to an optical recording medium which contains a benzobisazole-based compound in a recording layer of the optical recording medium. More specifically, the present invention relates to a novel optical recording medium which makes possible recording and reproduction using a laser beam selected from wavelengths of preferably 300 to 500 nm, more preferably 400 to 500 nm, particularly preferably 400 to 410 nm. Further, the present invention relates to a novel benzobisazole-based compound.

#An optical recording medium according to the present invention refers to an optical recording medium which data can be recorded in and reproduced from. However, hereinafter, a description will be given with reference to, as an appropriate example, an optical recording medium of the present invention which has a recording layer and a reflective layer on a substrate.

#The optical recording medium according to the present invention has, for example, a four-layer structure as shown in FIG. 1 in which a substrate 1, a recording layer 2, a reflective layer 3 and a protective layer 4 are built up in order. Alternatively, the optical recording medium has a laminated structure as shown in FIG. 2. That is, a medium shown in FIG. 2 has a structure in that a recording layer 2 is formed on a substrate 1, a reflective layer 3 is formed in close contact with the recording layer 2, and a protective layer 4 is laminated on the reflective layer 3 via an adhesive layer 5. However, another layer may exist under or on the recording layer 2, and another layer may exist on the reflective layer 3. Further, as shown in FIG. 3, the optical recording medium may have a structure that the substrate 1, the reflective layer 3, the recording layer 2 and the protective layer 4 are built up in the order presented and recording and reproduction are performed on the protective layer. Alternatively, it may have a medium structure as disclosed in Japanese Patent Application Laid-Open No. 326435/1998 in which a thickness of a light transmitting layer is defined by a laser light source wavelength λ of a reproduction system and a numerical aperture, N.A., of an objective lens. As for the compound of the formula (1) in the present invention, it can be used in an optical recording medium as described in Japanese Patent Application Laid-Open No. 203729/1999 which has two or more recording layers as required.