GB2290489A - Phthalocyanine dyes for optical recording - Google Patents

Abstract

The use of di(silicon phthalocyanine) compounds, aryloxy substituted phthalocyanine compounds and boron substituted phthalocyanine compounds as absorbers in optical recording and an optical recording medium, for use with a radiation recording beam of a given wavelength, comprising a substrate having on one side a recording layer which comprises one of such compounds which is capable of absorbing radiation of said given wavelength are disclosed.

Description

Optical Recordina Media This invention relates to an optical recording medium, in particular to an optical recording medium having a dye-containing recording layer.

Optical recording typically involves recording information onto an optical recording medium using a modulated light source, for example a laser, which medium may then subsequently be read, for example, with light of a different wavelength and/or reduced power to that of the recording light. One form of optical recording involves deformation or ablation of areas of the recording medium, for example by the formation of pits, as a result of the absorption by the medium of light from the light source. The size, shape and/or position of such deformed or ablated areas represents the information recorded on the medium.

Optical recording media may be in disc or tape form and usually comprise a substrate having a layer comprising recording material (recording layer) on one side into which the information may be recorded and a back coat on the reverse side to provide suitable handling properties. In order for the recording layer to absorb light from the light source, the recording layer conventionally comprises a dye compound which is selected to absorb light of a wavelength, for example in the visible or near infra-red region (400 to 1500nm wavelength), which is present in the light from the light source. The dye may be present as a pure material or as a mixture with a polymeric binder.

In addition to having an appropriate wavelength absorption band, it is necessary that the dye meets other criteria to facilitate production of optical recording media and to provide the media with good optical and physical characteristics.

Phthalocyanine and naphthalocyanine dyes have been disclosed for use in optical recording

media, for example, EP-A-391284 discloses the' use of bis(dimethyloctadecylsiloxy)silicon benzophthalocyanine in optical recording applications. Other mono (silicon phthalocyanines) such as rC4Hg(C6H5)2SiO]2 SiPc and [(nCeH13)3SiO]2 SiPc in which Pc represents an unsubstituted phthalocyanine, may also be used.

Typical problems which have been encountered in optical recording media dyes known in the art include poor wear with repeated reading of the information, poor ageing, difficulties in securing high resolution data storage and problems associated with production of the recording layer due to poor dye solubility and binder compatibility.

However, we have now found that compounds having two silicon phthalocyanine moieties (hereinafter referred to as di(silicon phthalocyanine) compounds), and aryloxy substituted phthalocyanine componds which have not hitherto been disclosed as suitable for use in optical recording media provide a desirable combination of characteristics which are required in optical recording media.

Accordingly, a first aspect of the invention provides an optical recording medium comprising a substrate having thereon a recording layer comprising a dye which is a di(silicon phthalocyanine) compound or a aryloxy substituted phthalocyanine compound.

Advantageously, the di(silicon phthalocyanine) compounds and the aryloxy substituted compounds employed in the present invention exhibit narrow absorption bands, in both the solid-state and in solution, when pure and desirably when mixed with a polymeric binder.

Preferably, the half band width in the solid state is not more than 120 nm and preferably not more than 70nm, for example 50 to 65 nm.

In solution, for example a 1% solution of the di silicon compound in dichloromethane, the half band width is preferably not more than 50 nm, more preferably not more than 30 nm, for example 10 to 20 nm. Similarly for a !% solution of an aryloxy compound in toluene, the half band width is preferably not more than 60nm, more preferably not more than 30nm.These narrow absorption bands provide for very high extinction coefficients, preferably at least 100000, more preferably at least 200000 and especially at least 280000 at the maximum absorption wavelength for the 1% solution of the dye. The high extinction coefficient provides for efficient light absorption and, further, such compounds may efficiently convert the absorbed light into heat with little fluorescence. This combination provides the practical benefit of excellent data writing.

Further advantage is provided as the compounds have improved thermal and photolytic stability thus providing good resistance to degradation of the recording medium with repeated reading of the information and/or with time. Such compounds may also exhibit a low level of saturation crystallisation and are thus suitable for high resolution data storage.

Suitably the di(silicon phthalocyanine) compound has the following formula (1): X-Si(Pc)-Y-Si(PC")-X" (1) wherein Pc' and Pc" represent, independently, an optionally substituted phthalocyanine group; X' and X" represent, independently, halogen, hydroxyl, an optionally substituted organic group containing 1 to 22 carbon atoms or, preferably, a group of formula (2) -Y'-SiAA'A" (2) wherein A, A' and A" represent, independently, halogen, hydroxyl or preferably a monovalent optionally substituted organic group containing 1 to 22 carbon atoms; and Y and Y' represent, independently, a divalent moiety linking two silicon atoms.

The precise properties of compounds of formula (1) may be tailoured to the particular application by provision of suitable substituents on the Pc', Pc", X and/or X" groups Si(Pc') and Si(Pc") are suitably of the following general structural formula (3):

Any one or more of the carbon atoms in positions 1 to 16 in Pc' and/or Pc" may be substituted in order to modify the properties of the compound (1) as compared with the unsubstituted analogue, for example by shifting the absorption band and the maximum absorption wavelength of the said compound.

Suitable substituted phthalocyanines include those in which at least one, for example all, of the carbon atoms in positions 1 to 16 are substituted. Suitable substituents include a halogen for example chlorine, hydroxyl, and/or a monovalent optionally substituted organic group containing 1 to 22 carbon atoms and which may comprise an aryl, alkyl, alkenyl, alicyclic, alkoxy and/or acyl moiety. Examples of preferred substituents include

Y and Y' are preferably 0 but may be selected from S, SO, SO2, NH, a divalent organic moiety which may comprise a aryl, alkyl, alkenyl, alicyclic, alkoxy and/or acyl moiety, for example an alkylene glycol linkage.

Where X' and/or X" is an optionally substituted organic group or a group of formula (II), X'and/or X" or, as the case may be, A, A' and/or A" are, independently, preferably aromatic, alicyclic or branched groups and are suitably aryl, alkyl, alkenyl, alkoxy and/or acyl groups and more preferably contain 4 to 22, preferably 4 to 12 and more preferably 4 to 10, carbon atoms for example butyl, phenyl, hexyl, cyclohexyl, naphthyl nonyl and alkoxy analogues thereof.

It is preferred that X' and/or X" is a relatively bulky group as this generally provides a beneficial increase in the solubility of compound (I) in organic solvents.

The improved solubility of the dye is advantageous as production of the media by a conventional solvent coating process is thereby facilitated. In such processes, the recording layer of the media is suitably formed on the substrate by depositing the dye from a solution comprising the dye in an organic solvent. Such processes are generally much simpler than other techniques, for example vacuum deposition, and also enable other components to be incorporated in the coating solution, for example a polymeric binder and other additives.

Preferred examples of compounds of formula (1) include rC4Hg(CeH )2SiO(SiPc)]2O and KC,H13SiO(SiPc)i2O in which Pc represents an unsubstituted phthalocyanine.

Preferably, the maximum absorption wavelength of the dye solid state spectrum is in the range 400 to 900 nm and more preferably 600 to 780 nm. A laser emitting light of about 685 nm wavelength is particularly suitable for use in optical recording and when such a laser is employed as the light source, it is preferred that the maximum absorption wavelength in the solid spectrum of the dye is in the range 630 to 740 nm, more preferably 640 to 700 nm. Where a 685nm laser is to be employed it is also preferred that the solution spectrum (1% in dichloromethane) of the dye is in the range 600 to 690 nm, especially 630 to 665 nm.

Compounds of formula (I) may be prepared by a multi-stage process for example as described in J. Am. Chem. Soc. Vol 106, No24, pages 7404 to 7410.

A further aspect of the invention provides a process for the production of a di(silicon phthalocyanine) compound which comprises hydrolysing a first silicon phthalocyanine compound, contacting at elevated temperature the hydrolysed first silicon phthalocyanine compound with a second silicon phthalocyanine compound, which may be the same or different as the first said compound, subsequently heating the said contacted first and second compounds in alkaline solution thereby to produce a di(silicon phthalocyanine) compound.

An example of a process for producing a compound of formula (I) is as follows: a silicon phthalocyanine compound may be obtained commercially or altematively, may be produced by heating a mixture of an optionally substituted 1,2-dicyanobenzene with a silicon compound, for example silicon tetrachloride, silicon tetraacetate and tetrapropenyl silicon. This phthalocyanine is then suitably hydrolysed in an alkaline, for example sodium hydroxide solution at elevated temperature for up to 24 hours and contacted, concurrently or successively with water to produce a dihydroxy silicon phthalocyanine. Altematively, hydrolysis of the phthalocyanine may be effected by heating with an alcohol, for example silyl alcohol, preferably in the presence of an organic solvent, for example dried 1 ,2,4-trimethylbenzene.

Suitably, the dihydroxy silicon phthalocyanine is then heated for up to 4 hours at about 220"C with a second silicon phthalocyanine which may be the same or different to the dihydroxy silicon phthalocyanine precursor and which is capable of combining with the dihydroxy silicon phthalocyanine, for example dichloro silicon phthalocyanine, desirably in the presence of a solvent, for example quinoline. Further heating for up to 4 hours, preferably in the presence of an alkali, for example sodium hydroxide, and a solvent, for example water suitably produces a compound having two hydroxy silicon phthalocyanine groups, which groups may be the same or different, linked by an oxygen atom.As desired, further reaction of this compound may be performed, for example by heating of this compound with a compound of formula ClSiAA'A" wherein A, A' and A" are as herein defined in the presence of a solvent, for example pyridine, suitably produces a siloxy substituted di(silicon phthalocyanine) which may then be purified.

Suitably, the aryloxy substituted phthalocyanines have Formula (4): (R),M gc(O-R'),(O-R2)2d (4) wherein: MkPc is a phthalocyanine nucleus of the Formula (5):

in which M is a metal atom; k is inverse of Y2 valency of M; R is a heterocyclic compound or a tertiary amine; each R' independently is an aryl or heterocyclic radical; each R2 independently is an alkyl or cycloalkyl; each X independently is -H or halogen; a is1 or2; b is an integer from 1 to 8; c is 0 or is an integer from 1 to 4; d is an integer from 4 to 15; and b+c+d = 16.

M is preferably a transition metal, more preferably a metal from the first transition row of the Periodic Table and especially iron, copper or cobalt. Where M is iron, copper or cobalt it is preferably present in the divalent state i.e. as Fe", Cu" or Co".

The heterocyclic compound represented by R preferably has one or more heteroatom(s) each of which has at least one pair of electrons and is capable of complexing with the central metal, M. The heterocyclic compound represented by R preferably contains at least one nitrogen, sulphur or oxygen atom as the heteroatom or contains a combination of such atoms. Suitable heterocyclic compounds include pyridine, quinoline, isoquinoline, pyrazine, pyrimidine, pyridazine, triazine, thiophene, furan, pyrrole, pyrazole, imidazole, thiazole, isothiazole, thiadiazole, oxazole, isooxazole, pyran, oxazine, morpholine, indole, bipyridyl each of which may be optionally substituted.Suitable optional substituents for the heterocyclic groups represented by R may be selected from C1.8-alkyl, C1.8-alkoxy, -NH2, -NHC1.6-alkyl, -N(C,.e-alkyl)2, -Cl, -F, -Br, -CN, -CF3, -NO2, -OH, C1.4-alkylphenyl, C 1.8-alkylC1-8-alkoxy,C1-8-alkoxyC1.8-alkyl and C1-8-alkoxyC1-8-alkoxy.

The heterocyclic compound represented by R is preferably an optionally substituted pyridine, quinoline, isoquinoline, and pyrazine, more preferably pyridine, quinoline, isoquinoline and pyrazine which are unsubstituted or which carry C,.ffi-alkyl, C1.4-alkylphenyl, C,."-alkoxy, -CN or -N(C1-8-alkyl) substituents and especially pyridine and pyridines substituted in the 2- and/or 4-positions by t-butyl, benzyl, -CN, -N(CH3)2 or-N(C2H 2.

The tertiary amine represented by R is preferably N(C1.,-alkyl)3 or arylN(C,.-alkyl)2, more preferably N(C,.4-alkyl)3 or phenyl N(C,.4-alkyl)2 and especially N(CH3)3, N(C2H)3, N(C4Hg)3, phenylN(CH3)2, phenylN(C2H 2 or phenylN(C4Hg)2.

Where the heterocyclic group represented by R has more than one heteroatom capable of complexing with the central metal, M, polymeric compounds of the following general Formula (6) may be formed.

wherein: R is a heterocyclic compound having two or more heteroatoms in which at least two heteroatoms are capable of complexing with the central metal; Z is equal to or greater than: 1 and M,Pc, R', R2, X, b, c and d are as hereinbefore defined. Such polymeric compounds form a further feature of the present invention.

The aryl and heterocyclicradicals represented by R' are each independently selected from optionally substituted mono- or bi-cyclic aromatic radicals or from optionally substituted mono- or bi-cyclic heterocyclic radicals. Examples of suitable aryl and heterocyclic radicals are phenyl, naphthyl especially 2-naphthyl, pyridyl, quinolinyl, isoquinolinyl, thiophenyl, furanyl, pyrimidyl, thiazolyl, isothiazolyl, benzothiazolyl and benzoisothiazolyl each of which may be optionally substituted.

Preferred aryl and heterocyclic radicals represented by R' are optionally substituted phenyl, 2-naphthyl and pyridyl.

Suitable substituents for the aryl or heterocyclic radicals represented by R' may be selected from C4,2-alkyl, preferably C48-alkyl and especially branched chain alkyl such as t-butyl and t-octyl; C0-alkoxy; C,,-cycloalkyl; aryl such as phenyl; -CN; -N(C110-alkyl)2 and C1.4-alkylaryl, preferably benzyl and especially those substituents which aid the solubility of the phthalocyanine in organic solvents.

The alkyl radical represented by R2 is preferably optionally substituted C,20-alkyll more preferably C,12-alkyl and especially C,8-alkyl. The cycloalkyl radical represented by R2 is preferably optionally substituted C310-cycloalkyl, more preferably C8-cycloalkyl and especially cyclohexyl.

Suitable optional substituents for the alkyl and cycloalkyl groups represented by R2 are any of those listed above as suitable substituents for the heterocyclic groups represented by R.

Each halogen represented by X is independently selected from fluoro, chloro, bromo and iodo, preferably chloro and bromo and more preferably chloro.

a is preferably 2.

b is preferably an integer from 4 to 8 and more preferably 4 or 8.

c is preferably 0 or 4, more preferably 0.

d is preferably an integer from 8 to 12.

In the compounds of Formula (4) it is preferred that the O-R' groups are substituted in the 2and 3-, the 6- and 7-, the 10- and 11- and the 14- and 15-positions of the phthalocyanine nucleus of Formula (2). Thus where b is 8 the O-R' groups preferably occupy the 2-, 3-, 6-, 7-, 10-, 11-, 14- and 15-positions. Where b is 4 two of the four pairs of positions i.e. 2- and 3- and/or 6- and 7- and/or 10and 11- and/or 14- and 15- are preferably occupied.

A first preferred sub-group of phthalocyanines of Formula (4) are those in which R is pyridine or pyridine substituted in the 2- and/or 4-positions by C,.4-alkyl, C1.4-alkylphenyl, -CN, or -N(C14-alkyl)2, or quinoline or isoquinoline; M is Fe", Cull or Co"; each R' independently is phenyl or naphth-2-yl optionally substituted by straight or branched chain C48-alkyl group; X is -H or halogen; a is2; b is8; c is 0; and d is8.

A second preferred sub group of phthalocyanines of Formula (4) are those in which R is pyridine or pyridine substituted in the 2- and/or 4-positions by C14-alkyl, C,-alkylphenyl, -CN or -N(C,.4-alkyl)2; or quinoline or isoquinoline; M is Fe", Cu" or Co"; each R' independently is phenyl or naphth-2-yl optionally substituted by straight or branched chain C,-alkyl group; each R2 independently is C,.-alkyl or C,,-cycloakyl; X is -H or halogen; a is2; b is 4; c is 4; d is8.

Particularly preferred phthalocyanines of Formula (4) and those of the first and second sub-groups are those in which M is Fe".

The phthalocyanines of Formula (4) of particular interest are those which have a maximum absorbance peak (max) in the 600 to 800nm region of the electromagnetic spectrum, preferably in the region 640 to 750nm and especially in the region 650 to 700nm and which have solubility of at least 1% in organic liquids. The organic liquids are selected from aliphatic, alicyclic and aromatic hydrocarbons, ketones, ethers, halogenated aliphatic and aromatic hydrocarbons, amides and substituted amides.

Particular examples of suitable organic liquids are toluene, cyclohexanone, methylethylketone, tetrahydrofuran (THF), chloroform, dichloromethane and dimethylformamide.

The phthalocyanines of Formula (4) may be prepared by firstly reacting a 2-dicyano benzene of Formula (7)

wherein X, X1, X2 and X3 each independently is H or halogen, provided at least one of X, X', X2 or X3 is halogen, with an optionally substituted phenol, R'OH to form a compound of Formula (8):

wherein Z, Z1, Z2 and Z3 each independently is H, halogen or -OR1, provided at least one of Z, zg, Z2 or Z3 is -OR' in which R' is as hereinbefore defined.

The compound of Formula (8), or a mixture of different compounds of Formula (8), is then reacted with an appropriate metal or metal salt, optionally in an inert liquid at elevated temperature to form a phthalocyanine of Formula (9).

MkPc(O-R')b(O-R5 (9) wherein M Pc, R1, R2, X, b, c and d are as hereinbefore defined.

In the above reaction appropriate metal salts include metal halides, metal oxides and metal hydroxides. For example where H is Fe, FeCI3 may be used as metal salt, where M is Cu, CuCI2 may be used as metal salt and where M is Co, CoBr2 may be used as metal salt.

Suitable inert liquids include halohydrocarbons such as 1-chloronaphthalene or 1 ,2,4-trichlorobenzene, nitrohydrocarbons such as nitrobenzene and diols such as ethylene glycol.

Suitable elevated temperatures are from 80 to 300"C, preferably from 100 to 250"C and especially from 100 to 200"C.

The compounds of Formula (4) may be prepared by reaction of a compound of Formula (9) with a heterocyclic compound or a tertiary amine represented by R. The process may optionally be carried out in an inert liquid medium and at an elevated temperature.

This reaction is preferably carried out in the heterocyclic compounds or the tertiary amine.

However, when an inert liquid medium is used this is preferably an organic liquid and more preferably is selected from aliphatic hydrocarbons such as dichloromethane, aromatic hydrocarbons such as 1-chloronaphthalene, and ethers such as tetrahydrofuran.

As stated above, the light source is, due to the ready availability and relatively low cost, commonly a semiconductor laser emitting light in the range 780-830 nm.

However, semiconductor lasers emitting in the 630-690 nm range are now becoming more readily available and such lasers, because they can be focussed to a smaller spot size, provide the possibility of greater data storage per unit area.

It is well known that phthalocyanine dyes are strong absorbers and that basic metal free phthalocyanine and copper phthalocyanine have absorption maxima in the region of 660nm which is ideal for the new lasers. However, the low solubility of such compounds makes them unsuitable for the formation of a recording layer.

It is also well known, that the solubility can be increased by suitable substituents. However, such substitution also has the effect of increasing the absorption maximum. Indeed, this route has been used to provide phthalocyanine dyes suitable for use with the longer wavelength lasers and reference may be made in this respect to EP 186404 and EP 391284.

Hence a further problem the invention seeks to solve is the provision of a an optical recording medium having a recording layer comprising a phthalocyanine compound which has increased solubility and an absorption maximum lying in the range 610-670 nm.

According to one aspect of the invention, there is provided an optical recording medium comprising a substrate having on one side a recording layer comprising a boron sub-phthalocyanine.

A boron atom is the only metallic atom small enough to be capable of stabilising a three comered (rather than the normal four cornered) phthalocyanine structure. Reducing the conjugation in the ring by 25% has the effect of reducing the absorption range by approximately the same amount resulting in an absorption range of 500-560 nm. Addition of substituent groups can increase this to 640-660 whilst at the same time conferring solubility.

Advantageously, boron sub phthalocyanine compounds employed in the present invention exhibit narrow absorption bands, in both the solid-state and in solution, when pure and desirably when mixed with a polymeric binder.

Preferably, the half band width in the solid state is not more than 120 nm and preferably not more than 70nm, for example 50 to 65 nm.

In solution, for example a 1% solution of the dye in toluene, the half band width is preferably not more than 60 nm. The narrow absorption band provides for extinction coefficients greater than 90,000 at the maximum absorption wavelength for a 1% solution of the dye in toluene. The high extinction coefficient provides for efficient light absorption and, further, such compounds may efficiently convert the absorbed light into heat with little fluorescence. This combination provides the practical benefit of excellent data writing.

Further advantage is provided as boron sub phthalocyanine compounds employed in the present invention have improved thermal and photolytic stability thus providing good resistance to degradation of the recording medium with repeated reading of the information and/or with time. Such compounds may also exhibit a low level of saturation crystallisation and are thus suitable for high resolution data storage.

The boron subphthalocyanine preferably comprises three optionally substituted isoindole units surrounding a boron atom. Each optional substituent, hereinafter referred to as R, which may be present in the isoindole units is preferably an alkyl, aryl, ether, thioether, halo, nitro, cyano, ester, acyl, sulpho, sulphonamide, carboxy or carbonamide group.

When R is alkyl it is preferably C1.4-alkyl. The preferred aryl substituents represented by R is optionally substituted anphthyl or phenyl. Preferred ethers and thioethers represented by R are alkyl and aryl ethers and thioethers, more preferably C1.4-alkyl, naphthyl, phenyl and tolyl ethers and thioethers.

When R is optionally substituted naphthyl or phenyl the optional substituents are preferably selected from halo, especially chloro; C1 ,-alkyl, especially methyl; nitro; C,4-alkoxy, especially methoxy and cyano.

When R is an ester group it is preferably -CO2T1 wherein T' is C14-alkyl or phenyl.

When R is an acyl group it is preferably -COT1 wherein T1 is as hereinbefore defined.

When R is a carbonamide group it is preferably -CONfTJ wherein T2 and T3 are each independently H, C1.4-alkyl or phenyl.

Preferably the boron subphthalocyanine is unsubstituted or has from 1 to 12, more preferably 3, 6, 9 or 12, substituents represented by R which are different to each other or the same as each other.

Examples of optional substituents represented by R include methyl, ethyl, n-propyle, iso-propyl, n-butyl, sec-butyl, tert-butyl, phenyl, methoxy, ethoxy, -SCH3, -SCH3, -SCH2CH3, naphthyloxy, naphthylthio, phenoxy, phenylthio, chloro, fluoro, bromo, nitro, cyano, methylphenylthio, methylphenoxy, methoxyphenoxy, methoxyphenylthio, nitrophenoxy, t-octylphenoxy, butoxyphenoxy and di-t-butylphenoxy.

A preferred boron subphthalocyanine is a compound of the formula (10)

Z is preferably boron substituted by a halogen, hydroxy or alkoxy Z iS preferably boron substituted by a halogen, hydroxy or alkoxy, more preferably by an alkyl, aryl or aryloxy group. The preferred halogen is Cl, F or Br; the preferred alkoxy group is C1-6-alkoxy; the preferred alkyl group is C1-6-alkyl, especially C1-4-alkyl; the preferred aryl group is phenyl; the preferred aryloxy group is phenoxy. Examples of boron substituted by the aforementioned groups include B-CI, B-F, B-CH3, B-OCH3, B-Phenyl, B-Br, B-OH and B-OCH2ch3.

R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11 and R12 are preferably each independently H or a substituent selected from those mentioned above for R.

It is preferred that R1 is identical to R5, R8, R9 or R12. Preferably R2 is identical to R6, R7, R10 or R11. R3 is preferably identical to R6, R7, R10 or R11. R4 is preferably identical to R5, R8, R9 or R12.

In one embodiment of the present invention R1, R4, R5, R8, R9 and R12 are identical to each other. In a second embodiment RI to R12 are identical to each other. In a third embodiment R2, R3, R6, R7, R10 and R11 are identical to each other and different from R1, R4, R5, R8, R9 and R12.

The phthalocyanines of Formula 10 of particular interest are those which have a maximum absorbance peak (A max) in the 630 to 750 nm region of the electromagnetic spectrum, preferably in the region 650 to 700 nm and especially in the region 650 to 680 and which have solubility of at least 1% in organic liquids. The organic liquids are selected from aliphatic, alicyclic and aromatic hydrocarbons, ketones, ethers, halogenated aliphatic and aromatic hydrocarbons, amides and substituted amides. Particular examples of suitable organic liquids are toluene, cyclohexanone, methylethylketone, tetrahydrofuran (THF), chloroform, dichloromethane and dimethylformamide.

The solubility of the dye is advantageous as production of the media by a conventional solvent coating process is thereby facilitated. In such processes, the recording layer of the media is suitably formed on the substrate by depositing the dye from a solution comprising the dye in an organic solvent.

Such processes are generally much simpler than other techniques, for example vacuum deposition, and also enable other components to be incorporated in the coating solution, for example a polymeric binder and other additivies.

A laser emitting light of about 685 nm wavelength is particularly suitable for use in optical recording and when such a laser is employed as the light source, it is preferred that the maximum absorption wavelength in the solid spectrum of the dye is in the range 630 to 740 nm, more preferably 640 to 700 nm. Where a 685 nm laser is to be employed it is also preferred that the solution spectrum (1% in toluene) of the dye is in the range 600 to 690 nm, especially 630 to 665 nm.

The recording layer of the optical recording media may also comprise a polymeric binder.

Conventional optical recording media binders may be employed including polystyrenes, for example polyhydroxystyrenes, polyethers, polyimides, polyurethanes, vinyl polymers, acrylic polymers and preferably polyesters. A particularly suitable binder comprises an amorphous polyester, for example VYLON 103 available from Toyobo.

The recording layer may comprise one or more dyes and be substantially free of polymeric binder. A binder-free recording layer is suitably employed where adhesion characteristics of the recording layer are not critical and where high sensitivity is required. for example in rigid disc applications. However, it is generally preferred that the recording layer comprises a dye and a polymeric binder to provide a desirable combination of adhesion and sensitivity. In such recording layers, the dye and polymeric binder are suitably present in a dye:binder weight ratio in the range 0.5 to 9:1 and preferably 1 to 7:1, for example 1:1, 3:1 and 7:1. The ratio of dye to binder may be varied for any particular dye and binder mixture to provide a suitable balance of characteristics including adhesion, rheology and optical performance.

Suitably the thickness of the recording layer is at least 20 nm and preferably at least 50 nm.

Suitably the recording layer thickness does not exceed 500 nm and is preferably not in excess of 200 nm. An especially preferred thickness for the recording layer is in the range 60 to 120 nm. The precise thickness of the recording layer is suitably selected depending on the required format of the media and sensitivity and adhesion requirements.

The substrate of the recording media according to the invention may be formed from any synthetic, film-forming polymeric material and, for optical tape applications, suitably has sufficient flexibility to function, when coated with the recording layer and any other desired layers, as a flexible optical tape medium which may be wound up on a spool in a similar manner to magnetic tape media.

Suitable thermoplastics materials include a homopolymer or copolymer of a 1-olefin, such as ethylene, propylene and but-l-ene, a polyamide, a polycarbonate, and, particularly, a synthetic linear polyester which may be obtained by condensing one or more dicarboxylic acids or their lower alkyl (up to 6 carbon atoms) diesters, eg terephthalic acid, isophthalic acid, phthalic acid, 2,5- 2,6- or 2,7naphthalenedicarboxylic acid, succinic acid, sebacic acid, adipic acid, azelaic acid, 4,4'diphenyldicarboxylic acid, hexahydroterephthalic acid or 1 ,2-bis-p-carboxyphenoxyethane (optionally with a monocarboxylic acid, such as pivalic acid) with one or more glycols, particularly aliphatic glycols, eg ethylene glycol, 1,3- propanediol, 1,4- butanediol, neopentyl glycol and 1,4-cyclohexanedimethanol.

A polyethylene naphthalate, and particularly a polyethylene terephthalate film is preferred, especially such a film which has been biaxially oriented by sequential stretching in two mutually perpendicular directions, typically at a temperature in the range 70 to 125"C, and preferably heat set, typically at a temperature in the range 150 to 250"C, for example - as described in British Patent GB-A-838708.

The thickness of the substrate of a medium according to the invention may vary over a wide range, but generally will be up to 300, especially from 2 to 75 ,um.

The substrate may require a surface treatments or provision of a subbing or receptive layer in order to improve adhesion of the recording layer and/or the back coat layer to the substrate.

For optical recording media applications, the substrate is suitably coated with or presents a highly reflective layer comprising for example aluminium, on the recording layer side of the substrate.

Typically there is a smoothing layer provided between the substrate and the reflective layer. The recording layer may be protected by a conventional over coat. The overcoat layer suitably comprises a material which is highly transmissive to the radiation used for writing and reading the medium and which is suitably compatible with the reverse side of the substrate and may also serve to protect the recording layer from the environment and from damage by for example abrasion. The over coat layer is preferably composed of an organic material; such organic material may be a cross-linked plastics material which may be thermally or radiation curable. We do not, however, exclude the possibility that the over coat may be composed of an inorganic material or a composite of an organic and inorganic material.Suitable materials are readily apparent to the skilled man and include for example uv and electron beam curable urethane acrylates, epoxy acrylates and polyester acrylates.

The thickness of the over coat is suitably selected according to the intended method of optical recording. For example, where media are to be employed in an ablative recording method in which the over coat is breached by the recording light, the over coat is preferably of a thickness not in excess of 100 nm. In a non-ablative recording method, the over coat is suitably of a thickness in the range 150 to 350 nm and preferably 240 to 280 nm. The thickness of the over coat is suitably selected to provide a desirable balance of wear, sensitivity and optical characteristics.

Recording media according to the present invention may comprise a back coat in order to impart desirable handling characteristics to the media. Conventional back coats comprising a plastics material, for example an acrylate resin, with an inorganic filler, for example silica, incorporated therein may be employed, however, the back coat is preferably a polymeric surface textured back coat wherein at least part of the texture is provided by the polymer as disclosed in our European Patent Application No 92305216 (EP-A-519629).

One or more of the layers of a media according to the invention may conveniently contain any of the additives conventionally employed in the manufacture of recording media. Thus, agents such as anti-static agents, dyes, pigments, voiding agents, lubricants, anti-oxidants, anti-blocking agents, surface active agents, slip aids, ultra-violet light stabilisers, viscosity modifiers and dispersion stabilisers may be incorporated in the substrate and/or other layer(s) as appropriate.

The recording layer and other layers which are optionally present in the recording medium are suitably coated onto the substrate using conventional coating techniques for example web coating and spin coating.

The invention is illustrated by the following non-limiting examples.

Example 1 A di(silicon phthalocyanine) compound was prepared as follows: dichlorosilicon phthalocyanine (available from Aldrich Chemicals) was heated at 1 OO"C for 20 hours in the presence of excess aqueous sodium hydroxide and quinoline; the reaction mixture was then poured into an acetone/water mixture to produce dihydroxysilicon phthalocyanine (DHSP) which was then dried.The solid DHSP was then ground together with dichlorosilicon phthalocyanine (1 tyo 1 mole parts), heated at 220"C for 4 hours in the presence of quinoline, subsequently combined with sodium hydroxide and water and heated under reflux for 4 hours, cooled in an acetone/water mixture and filtered washed and dried to produce [HO(SiPc)]2O. This compound was then combined with 3 equivalents of t-butyldiphenyl silicon chloride (available from Aldrich Chemicals) and heated under reflux for 6 hours under nitrogen in the presence of dry pyridine, the reaction mixture was then cooled with an acetone/water to mixture, dissolved in dicloromethane and filtered, the solvent was removed from the filtrate and the product was then added to a 2::1 mixture of acetone and methanol which was then concentrated to yield a precipitate of rC4H9(C0H2O(SiPc)2O having the properties as shown in Table 1.

Example 2 The procedure of Example 1 was repeated with the exception that the t-butyldiphenyl silicon chloride in Example 1 was replaced by trihexyl silicon chloride to produce [(C,H,d,O(SiPc)l,O having the properties as shown in Table 1.

ExamDle 3 Optical recording media according to the present invention were prepared by spin coating onto a polyethylene terephthalate substrate (available from ICI under the trade name MELINEX) having an aluminium layer, a series of dye compositions as listed below: the coated composition was dried at 60"C until there was no further change in the reflectivity of the coated substrate to provide a recording layer on the substrate having a thickness of 110 nm.

ComPosition 3A Dye as produced in Example 1 in a toluene solvent.

ComDosition 3B Dye as produced in Example 1 and WLON 103 (polyester binder available from Toyobo) in a dye:binder ratio of 3:1 in a toluene solvent (0.759 dye, 0.259 binder in 26ml toluene).

ComDosition 3C Dye as produced in Example 2 in a toluene solvent.

Composition 3D Dye as produced in Example 2 and WLON 103 (polyester binder available from Toyobo) in a dye:binder ratio of 1:1 in a toluene solvent (0.759 dye, 0.759 binder in 30ml toluene).

In all of the compositions 3A to 3D the dye was readily soluble in the solvent thus allowing a conventional coating process to be employed. All the compositions, when coated onto the aluminmised substrate provided a smooth recording layer and had a low level of crystallisation, rendering them suitable for high resolution data storage.

Table 1 Prnoertv ExamPle 1 ExamDle 2 Bandwidth (1% weight solution in dichloromethane) 15 nm 14nm Melting point > 300"C I 97-2000C Maximum absorption wavelength (solid-state) 667 nm 646nm " (1 % dichloromethane solution) 635nm 632nm Extinction coefficient (Emax) 313000 291000 Examole 4 PreDaration of octa-4,5-(4-t-octylphenoxy)iron(II)phthalocyanine.dipyridine i) Preoaration of 4.5-DichloroDhthalicanhvdride 4,5-Dichlorphthalic acid (250.769, 1.07mol) was stirred and heated at reflux in acetic anhydride (505cm3) for 16 hours.The reaction mixture was cooled and the solid collected by filtration and washed with toluene (750cm3) to yield the 4,5-dichlorophthalicanhydride (177.669, 77%) as a pale yellow solid, m.p. 183-186"C; max (KBr) 1831 (C=0), 1784 (C=0) cm-1.

ii) PreDaration of 4.5-Dichloroohthalamide 4,5-Dichlorophthalicanhydride (190.12g, 0.88mol) was stirred and heated at approximately 210 C with urea (52.89, 0.88mol) for 16 hours. The reaction mixture was cooled and the solid was ground and then stirred in water (200cm3) for 1 hour. The resulting solid was collected by filtration and washed with water (1000cm3) and then dried in air to yield the 4,5-dichlorophthalamide (182.69, 96%) as an off-white solid, max (KBr) 3430, 3304, 3146 (NH2), 1688 (C=0), 1667 (C=0) cm1.

iii) Preoaration of 4.5-Dichlornhthalamide 4,5-Dichlorophthalamide (176.29, 0.81 8mol) and concentrated ammonia solution (1825cm3) were stirred together at room temperature for 16 hours. The resulting solid was collected by filtration, washed with water (4 litres) and dried at 50 C over calcium chloride to yield the 4,5-dichlorophthalamide (182.69, 96%) as an off-white solid, max (KBr) 3430, 3304, 3146 (NH2), 1688 (C=0), 1667 (C=0) cm-1.

iv) Preoaration of 4.5-Dichloroohthalonitrile A solution of the 4,5-dichlorophthalamide (182.69, 0.78mol) in pyridine (1.3 litres) was cooled to 0 C and phosphorus oxychloride (187cm3) was added dropwise over 1 hour maintaining the temperature below 0 C. The mixture was allowed to warm to room temperature and left to stand for 48 hours during which time a brown purple colour developed. The mixture was poured into ice/water (5 litres) and the solid was collected by filtration and washed with ice/water (1.5 litres) and cold methanol (500ml) and then dried in vacuo to leave a brown solid.The solid was recrystallised from acetone and waterto yield the desired 4,5-dichlorophthalonitrile (120.59, 86%) as a beige solid, m.p. 178-181 C; max (KBr) 2238 (CN) cm~'; Found: %C 49.1, %H 1.2, %N 14.3. C,H2N2C12 requires %C 48.7, %H 1.0, %N 14.2.

v) Preparation of 4.5 < li(4-t-octylphenoxv)phthalonitrile 4,5-Dichlorophthalonitrile (9.859, 0.05mol), t-octylphenol (22.79, 0.11mol) and potassium carbonate (15.29, 0.11 mol) in N,N-dimethylformamide (75cm3) were stirred and heated at 120"C for 2 hours and then allowed to cool to room temperature. Water (100ml) was added and the resulting solid was collected by filtration through filter aid (clarcel-flo) and washed with water. The solid was dissolved in dichloromethane (250cm3) and washed from the filter aid, and then washed with water (250cm), 5% potassium hydroxide in water (200cm3) and then water (3x200cm3), dried (MgSOJ, carbon screened and then evaporated to dryness in vacuo to leave a solid.The solid was recrystallised from acetone and water to yield 4,5-di(4-t-octylphenoxy) phthalonitrile (15.599) as a pale solid, m.p. 168-171 C.

vi) Preparation of octa-4.5-(4-t-octvlphenoxy)irnnphthalocvanine The 4,5-di(4-t-octylphenoxy)phthalonitrile (8.529, 0.016mol), iron (III) chloride hexahydrate (1.429, 0.0053mol), urea (0.319, 0.0052mol) and ammonium molybdate (0.00629, 3.16 x 10-5mol) were stirred at 190-210"C for 35 minutes. 1-Chloronaphthalene (5cm3) was then added to mobilise the mixture and heating and stirring was continued for a further 25 minutes after which time the mixture was then allowed to cool to approximately 50"C and methanol (50cm) was added.The resulting suspension was stirred at room temperature for 14 hour and the solid was collected by filtration and washed with methanol. The solid was then dissolved in toluene and passed through silica gel eluting with a solution of 20% ethyl acetate in toluene. The combined eluent was concentrated and methanol was added to precipitate a solid which was collected by filtration and washed with methanol to yield octa-4,5-(4-t-octylphenoxy)ironphthalocyanine (7.369) as a dull green solid, m.p. 280-320"C; max (toluene) 657nm (Emax 71,000).

vii) Preparation of octaA.5-di(4-t-octvlphenoxv)iron(ll)phthalocvanine. dipyridine A suspension of octa-4,5-(4-t-octylphenoxy)iron (29) in pyridine (80cm) was stirred and heated at reflux for 15/4 hours and the allowed to cool to room temperature. The resulting precipitate was collected by filtration and washed with methanol (25cm3) and then dried in air to yield octa-4,5-di(4-t-octylphenoxy)iron(ll)phthalocyanine.dipyridine (1.55g) as a bright green solid, m.p.

> 300 C; max (toluene) 658nm (Emax 152000).

Examole 5 Optical recording media were prepared in the same way as in Example 3 using the compositions: Composition 5A Dye as produced in Example 4 in a toluene solvent.

Composition 5B Dye as produced in Example 4 and VYLON 103 (polyester binder available from Toyobo) in a dye:binder ratio of 3:1 in a toluene solvent (0.759 dye, 0.259 binder in 26ml toluene).

In all of the compositions 3A to 3D the dye was readily soluble in the solvent thus allowing a conventional coating process to be employed. All the compositions, when coated onto the aluminised substrate provided a smooth recording layer and had a low level of crystallisation, rendering them suitable for high resolution data storage.

Examole 6 PreDaration of the comoounds of Formula (10) wherein Rlto L; are 4-methvlohenvithio and Z is B-Ph. B-CI. B-OCH1 or B-OH Phenyldichloroborane (3.869, 0.0243 mol) was added dropwise to a stirred solution of tetra-4-methylthiophenylphthalonitrile (preparable by condensation of 4-methylthiophenol and tetrachlorophthalonitrile) (10g, 0.0162 mol) in l-chloronaphthalene (20 ml) at 200"C under an atmosphere of nitrogen. The mixture was stirred at 250"C under nitrogen for 30 minutes and then allowed to cool to room temperature.The mixture was drowned out into methanol (200 ml) and the supematant liquid decanted off to leave a bluish-green gum. The gum was triturated with methanol (2 x 200ml) to give a solid which was placed in a soxhlet thimble and extracted under reflux with methanol for 30 hourse. The remaining solid was collected by filtration as a mixture of differently substituted boron subphthalocyanines.The individual components were separated by column chromatography on silica eluting with: (i) hexane 3:1 dichloromethane to give a mixture of the title compounds wherein Z is B-Ph/B-CI (0.5g, 5%) as a bluish-green solid, m.p. 155-165 "C and lambda max (CH2CLJ 640nm (E max 97800); (ii) hexane 1:1 dichloromethane gave the title compound wherein Z is B-OCHl (1.39G, 14%) as a bluish-green solid, m.p. 130-140"C; lambda max (CH2CI2) 635 nm E max 99500); (iii) hexane 10:1 dichloromethane gave the title compound wherein Z is B-OH (0.39, 3%) as a greenish-blue solid, m.p. 140-160"C; lambda max (CH2CI2) 630 nm (E max 98100).

ExamDle 7 Preparation of the compound of Formula (10) wherein R: to Ra are 2-naphthvloxv and Z is B-Cl Staae a A mixture of tetrachlorophthalonitrile (26.59, 0.1 mol), 2-naphthol (869, 0.6 mol) and potassium carbonate (55.59, 0.4 mol) in dimethylformaide (200 ml) was stirred and heated at 120"C for 2 hours. The mixture was cooled, drowned out into water (500 ml) and extracted using dichloromethane (2x200 ml). The combined organic extracts were washed with aqueous 5% potassium hydroxide and water. The organic layer was dried (MgSO4), carbon screened and evaporated to dryness in vacuo to leave a solid.The solid was crystallised from acetonelwater to yield tetra(2-naphthyloxy)phthalonitrile (42.649, 69.6%) as a pale yellow powder, m.p. 196-198"C.

Staae b Phenyldichloroborane (0.299, 1.8 mmol) was added dropwise to a stirred solution of tetra(2-naphthyloxy)phthalonitrile (5g, 7.18 mmol) in l-chloronaphthalene (12 ml) at 200"C under an atmosphere of nitrogen. The resultant mixture was stirred at 250"C under nitrogen for 10 minutes then allowed to cool to room temperature. The mixture was drowned out into methanol (100 ml) and the resultant precipitate collected by filtration and washed with methanol to leave a blue solid. The solid was purified by column chromatography on silica eluting with hexane 3:2 dichloromethane to give the title compound (0.1759, 1.1%) as a reddish-blue gum; lambda max (CH2C12) 608.4 nm (E max 71000).

Examole 8 Preparation of the compounds of Formula (10) wherein Z is B-OCH1or a mixture of -B-CI/-B-Ph and R2 R R RQ. R and R" are 2-naphthvlthio Staae a 2-Thionaphthol (16.989, 0.106 mol) was added to a stirred solution of sodium methoxide (6.05g, 0.112 mol) in methanol (50 ml) under nitrogen. The mixture was stirred for 1 hour and then added dropwise over 1 hour to a stirred solution of 4,5-dichlorophthalonitrile (10g, 0.0507 mol) in methanol (100 ml). The resultant suspension was stirred and heated under reflux for 2 hours and then cooled and drowned out into water (300 ml).The solid was collected by filtration, filtered through a pad of silica, eluting with toluene, and the filtrate evaporated to dryness in vacuo to give a solid which was crystallised from acetone/water to yield 4-2-thionaphthyl)-5-chlorophtalonitrile (11.29, 68%) as a white solid, m.p. 209-212"C.

Staae b 2-Thionaphthol (11.099, 0.069 mol) was added to a stirred solution of sodium methoxide (3.929, 0.073 mol) in methanol (50 ml) under nitrogen. the mixture was stirred for 1 hour and then added dropwise over 1 hour to a stirred solution of 4-(2-thionaphythyl)-5-chlorophthalo nitrile (119, 0.0345 mol) in methanol (100 ml). The resultant suspension was stirred and heated under reflux for 3 hours and then cooled and drowned out into water (400 ml). the solid was collected by filtration, dissolved in dichloromethane (41) and washed with 10% aqueous potassium hydroxide (2 x 11), then water (11) and dried (MgSOj and evaporated to dryness in vacuo to leave an off-white solid which was recrystallised from toluene to give 4,5-di(2-thionaphthyl) phthalonitrile (12.39, 80%) as a white fluffy solid, m.p. 244-246"C.

Staae c Phenyldichloroborane (1.229, 7.71 mmol) was added dropwise to a stirred solution of 4,5-di(-2-thionaphthyl)-phthalonitrile (2.159, 4.86 mmol) in 1-chloronaphthalene (10 ml) at 200"C under an atmosphere of nitrogen. The resultant mixture was stirred at 250"C under an atmosphere of nitrogen. The resultant mixture was stirred at 250"C for 10 minutes and then allowed to cool to room temperature. The mixture was drowned out into methanol (100 ml) and the resultant precipitate collected by filtration and washed with methanol to leave a blue solid. The solid was placed in a soxhlet thimble and washed with refluxing methanol for 18 hours.The remaining solid was purified by column chromatography on silica eluting with hexane 1:1 dichloromethane to give the title mixture where Z is -B-CI/-B-Pn as a reddish-blue solid, m.p. 160-170"C (dec); lambda max (CH2CI > ) 605 nm (E max 64000). Elution with hexane 1:3 dichloromethane gave the title compound wherein Z is B-OCH3 (0.03G) as a reddish-blue solid, m.p. 135-140"C-(dec) lambda max 600 nm (E max 80000).

ExamDle 9 Preparation of a comoound of Formula (10) wherein R . RZ Z RIP and R" are 4-nitroDhenoxv and Z is B-Ph) A mixture of 4,5-dichlorophthalonitrile (1so, 0.076 mol), 4-nitrophenol (21.299, 0.153 mol), potassium carbonate (21.29, 0.153 mol) in dimethylformamide (100 ml) was stirred at 1200C for 2 hours and cooled to room temperature before adding to water (250 ml). The mixture was extracted using dichloromethane (2 x 100 ml) and the combined organic extracts washed with water, with 5% potassium hydroxide and water (2 x 100 ml). The organic phase was dried (MgSO ), carbon screened and evaporated to dryness in vacuo.The resultant solid was crystallised from acetone and water to yield 4,5-bis(4-nitrophenoxy)phthalonitrile (8.219, 36.5%) as a yellow solid.

Phenyldichloroborane (0.9g, 5.6 mmol) was added dropwise to a stirred solution of 4,5-bis(4-nitrophenoxy)phtalonitrile (I .5g, 3.73 mmol) in I-chloronaphthalene (5ml) at 200 C under an atmosphere of nitrogen. The resultant solution was stirred and heated at 250 C under nitrogen for 30 minutes, allowed to cool to room temperature and then drowned out into methanol (100 ml). The resultant solid was purified by column chromatography on alumina eluting with dichloromethane to yield the title compound as a magenta solid, m.p. 235-255"C (dec); lambda max (CH2CI2) 570 nm.

ExamDle10 PreDaration of the compound of Formula (10) wherein R1to R12 are chloro and Z is a mixture of B-Ph and B-CI Phenyldichloroborane (1.3 mls, 0.013 mol), was added dropwise to a stirred solution of tetrachlorophthalonitrile (lOg, 0.038 mol) in 1-chloronaphthalene (20 ml) at 240 C under an atmosphere of ntirogen. The mixture was then stirred and heated for 214 hours at 240"C. The mixture was allowed to cool to room temperature and drowned into methanol (200 mls). The product precipitated along with unreacted starting material and was filtered off under vacuum.

Starting material was removed from the crude mixture by column chromatography on silica, eluting with dichloromethane. A bluish-red solid was isolated and found to be a mixture of 3 differently substituted sub-phthalocyanines all of which gave fluorescent bands on t.l.c. (eluting with 1:1 hexane:dichloromethane), r.f. values (1) 0.84 major product (isolated); (2) 0.66 minor product; and (3) 0.54 minor product.

The major product (1) was isolated by column chromatography on silica, eluting with 1:1 hexane:dichloromethane as a bluish-red solid (0.5g, 6.2%); m.p. 184-188"C; lambda max (CH2CI2) 587 nm; the major product being Z = B-CI, with minor amounts of Z=B-Ph.

Examole 11 Preparation of a comoound of Formula (10) wherein R1 to Ra are H and Z is B-Ph Phenyldichloroborane 93.19, 0.02 mol) was added dropwise to a stirred solution of diiminoisoindoline (i 1.329, 0.078 mol) in l-chloronaphthalene (20 ml) at 200"C under an atmosphere of nitrogen. The mixture was stirred and heated to 260"C for 1 hour and then allowed to cool to room temperature. The mixture was drowned into methanol (400 ml) and the precipitated starting material filtered off to leave a dark red filtrate which was extracted with n-Hexane (5 x 250 ml).Solvent was evaporated from the combined extract to give a crude product which contained some i-chloronaphthalene. The crude product was dissolved in dichloromethane (40 ml) and purified by column chromatography on silica, eluting with dichloromethane to yield the title product as a magenta solid (0.20 g, 2.4%), m.p. 122-124"C, lambda max (CH2CIJ 558 nm, m/z 472 (M+(Ph), 52%).

Example 12 Optical recording media according to the present invention were prepared by spin coating onto a polyethylene terephthalate substrate (available from ICI under the trade name MELINEX) having an aluminium layer, a series of dye compositions as listed below: the coated composition was dried at 60"C until there was no further change in the reflectivity of the coated substrate to provide a recording layer on the substrate having a thickness of 110 nm.

Composition 7A Dye as produced in Example I (ii) in toluene as solvent.

Composition 7B Dye as produced in Example 1 (ii) and VYLON 103 (polyester binder available from Toyobo) in a dye:binder ratio of 3:1 in toluene as solvent (0.789 dye, 0.269 binder in 17ml toluene).

Composition 7C Dye as produced in Example 1 (i) and VYLON 103 in a dye:binder ratio of 3:1 in toluene as solvent (0.51g dye, 0.179 binder in 16 ml toluene).

Composition 7D Dye as produced in Example 1 (iii) and VYLON 103 in a dye:binder ratio of 1:1 in toluene as solvent (0.119 dye, 0.119 binder in 6ml toluene).

In all of the compositions 7A to 7D the dye was readily soluble in the solvent thus allowing a conventional coating process to be employed. All the compositions, when coated onto the aluminmised substrate provided a smooth recording layer and had a low level of crystallisation, rendering them suitable for high resolution data storage.

Table 1 Prooertv ExamDle 1 (i) Example 1 (ii) Example I (iii) Bandwidth (in nm) solid state 55 64 53 1% weight solution 55 49 53 in toluene Maximum absorption wavelength (in nm) (solid-state) 653 647 635 (1% dichloromethane solution) 640 635 630 Extinction coefficient (EmZ) 97800 99500 98100

Claims (5)

1. Claims 1. An optical recording medium comprising a substrate having thereon a recording layer comprising a dye which is a di(silicon phthalocyanine) compound or a aryloxy substituted phthalocyanine compound.
2. 2. An optical recording material according to Claim 1, in which the di(silicon phthalocyanine) compound has the following formula: X'-Si(Pc')-Y-Si(Pc")-X" wherein Pc' and Pc" represent, independently, an optionally substituted phthalocyanine group; X' and X" represent, independently, halogen, hydroxyl, an optionally substituted organic group containing 1 to 22 carbon atoms or, preferably, a group of formula -Y'-SiAA'A" wherein A, A' and A" represent, independently, halogen, hydroxyl or preferably a monovalent optionally substituted organic group containing 1 to 22 carbon atoms; and Y and Y' represent, independently, a divalent moiety linking two silicon atoms.
3. 3. An optical recording material according to Claim 1, in which the aryloxy substituted phthalocyanines have the formula: (R),MkPc(O-R1)b(0-R5 wherein: MkPc is a phthalocyanine nucleus of the formula

   in which M is a metal atom; k is inverse of 5M2 valency of M; R is a heterocyclic compound or a tertiary amine; each R1 independently is an aryl or heterocyclic radical; each R2 independently is an alkyl or cycloalkyl; each X independently is -H or halogen; a islor2; b is an integer from 1 to 8; c is 0 or is an integer from 1 to 4; d is an integer from 4 to 15; and b+c+d = 16.
4. 4. An optical recording medium comprising a substrate having thereon a recording layer comprising a dye which is a boron sub-phthalocyanine.
5. 5. An optical recording material according to Claim 4, in which the boron subphthalocyanine is a compound of the formula:

   wherein: Z is optionally substituted boron; and R',- 12are each independently H or a substituent