Indole compound, optical filter and optical recording material

#This invention relates to a novel indole compound, an optical filter, and an optical recording medium. The indole compound is useful as an optical element and the like. The indole compound is particularly useful as an ultraviolet (UV) absorber incorporated into an optical filter for application to image displays. It is also useful as an optical recording material for use in optical recording media capable of high density optical writing and reading with low energy lasers having wavelengths in the visible to near infrared regions.

#Optical recording media have been widespread generally because of their superiority such as high recording capacity and non-contact write/read system. Recordable optical disks such as WORMs, CD-Rs, and DVD-Rs record information by irradiating a very small area of the optical recording layer with a focused laser beam to change the properties of the irradiated area and reproduce the recorded information making use of the difference in reflected light quantity between the recorded area and the non-recorded area.

#Wavelengths of semiconductor lasers used in writing and reading information on the currently available optical disks of the type described are in the ranges of 750 to 830 nm for CD-Rs and of 620 to 690 nm for DVD-Rs. In pursuit of a further increased capacity, optical disks using shorter wavelength lasers have been under study. For example, those using a write wavelength of 380 to 420 nm have been studied.

#The indole compound and the optical filter and optical recording material containing the indole compound will be described in detail with reference to their preferred embodiments.

#The indole compound of the invention is described first.

#In general formula (I), examples of the hydrocarbon group having 1 to 30 carbon atoms represented by R1, R2, R5, R6, R7, and R8 include alkyl groups, such as methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, tert-butyl, isobutyl, amyl, isoamyl, tert-amyl, hexyl, cyclohexyl, cyclohexylmethyl, 2-cyclohexylethyl, heptyl, isoheptyl, tert-heptyl, n-octyl, isooctyl, tert-octyl, 2-ethylhexyl, nonyl, isononyl, decyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, and octadecyl; alkenyl groups, such as vinyl, 1-methylethenyl, 2-methylethenyl, propenyl, butenyl, isobutenyl, pentenyl, hexenyl, heptenyl, octenyl, decenyl, pentadecenyl, and 1-phenylpropen-3-yl; phenyl; naphthyl; alkylaryl groups, such as 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, 4-vinylphenyl, 3-isopropylphenyl, 4-isopropylphenyl, 4-butylphenyl, 4-isobutylphenyl, 4-tert-butylphenyl, 4-hexylphenyl, 4-cyclohexylphenyl, 4-octylphenyl, 4-(2-ethylhexyl)phenyl, 4-stearylphenyl, 2,3-dimethylphenyl, 2,4-dimethylphenyl, 2,5-dimethylphenyl, 2,6-dimethylphenyl, 3,4-dimethylphenyl, 3,5-dimethylphenyl, 2,4-di-t-butylpheyl, and cyclohexylphenyl; arylalkyl groups, such as benzyl, phenethyl, 2-phenylpropan-2-yl, diphenylmethyl, triphenylmethyl, styryl, and cinnamyl; and the above recited hydrocarbon groups interrupted by an ether and/or a thioether linkage, such as 2-methoxyethyl, 3-methoxypropyl, 4-methoxybutyl, 2-butoxyethyl, methoxyethoxyethyl, methoxyethoxyethoxyethyl, 3-methoxybutyl, 2-phenoxyethyl, 3-phenoxypropyol, 2-methylthioethyl, and 2-phenylthioethyl. These hydrocarbon groups may be substituted, e.g., with an alkoxy group, an alkenyl group, a nitro group, a cyano group, or a halogen group. When the hydrocarbon group is substituted with one or more groups selected from alkoxy groups, alkenyl groups, and a cyano group, the total carbon atom number of the hydrocarbon group inclusive of the substituent(s) is 30 at the most.