The field of the invention is the optical storage of information on write-once storage media, the information pits being differentiated by the different optical properties of a colorant at written and unwritten sites. This technology is usually termed "WORM" (for example "CD-R", "DVD-R", "DVD+R"); those terms have been retained herein.

By the use of compact high-performance diode lasers that emit in the range of from 630 to 690 nm, it is possible in principle to achieve a 4- to 5-fold improvement in data packing density and a 6- to 8-fold increase in storage capacity in comparison with media having a blue or green layer, in that the track pitch (distance between two turns of the information track) and the size of the pits can be reduced, for example, to approximately half the value in comparison with conventional CDs.

This imposes extraordinarily high demands on the recording layer to be used, however, such as high refractive index, uniformity of script width at different length pulse durations and also high light stability in daylight with, at the same time, high sensitivity to high-energy laser radiation. The known recording layers possess those properties only to an unsatisfactory extent.

J P-A-11/213442 discloses an optical recording medium of geometry suitable for use in the range from 620 to 690 nm, comprising a metal complex of a heterocyclic

azo ligand of the formula While A may be substituted by both an electron-donating or an electron-attracting group, however, B may only be substituted by an electron-donating group.

Leitmotifs in the whole prior art are that a dialkylated amino group in the para- position to the azo group and the complexation with a metal are essential for good performance in optical information media.

EP-A-1 170339 discloses styryl dyes of the generic formula

X , wherein, among other formulae, X may be a

complex of structure . Ri6 and Ri ₇ , however, do not

comprise any deprotonated group. Furthermore, the only example of such complex (chemical formula 8), while lacking embodiment, shows protonated heterocyclic rings (R19/R20) with the metal in the oxidation state +1.

WO 2004/088649 discloses a broad choice of heterocyclic metal complex dyes, for example of structure:

It is disclosed that it is possible to combine these metal complex dyes with other, known chromophores, including the azo dyes and azo metal complexes of JP-A-11/028865 and the styryl dyes of US-6,103,331.

PCT/ EP2005/053215 is a patent application according to Art. 54(3) EPC and Rule 64.3 PCT, which is directed to metal complex dyes comprising the instant ligands and cations.

However, the properties of the known recording media still leave something to be desired, especially in respect of the optical properties (high n, low k) and quality of recordings using a laser of a wavelength around 658 ±5 nm (DVD-R or DVD+R,

hereafter DVD±R).

The aim of the present invention is to provide an optical recording medium, the recording layer of which has high storage capacity combined with excellent other properties. Such a recording medium should be both writable and readable at the same wavelength in the range of from 600 to 700 nm (preferably from 630 to

690 nm).The main features of the recording layer according to the invention are the very high initial reflectivity in the said wavelength range of the laser diodes, which can be modified with great sensitivity; the high refractive index; the good uniformity of the script width at different pulse durations; the excellent light and multiple read stability; and the good solubility in polar solvents, as well as excellent compatibility with laser sources of different wavelengths both for recording and for playback.

Very surprisingly, by the use of salts of certain non-metallized, organic anions having particular substituents and ammonium or phosphonium cations (preferably heterocyclic, especially styryl cations) as recording layer or as an additive to the recording layer, it has been possible to provide an optical recording medium having properties that are astonishingly better than those of the recording media known hitherto. The refractive index in the solid layer is astonishingly very high. The layers are unexpectedly neither hygroscopic nor moisture-sensitive and possess a high environmental, light and multiple read stability. The solubility is high and the optical parameters are excellent.

The invention accordingly relates to an optical recording medium comprising a substrate, a reflecting layer and a recording layer, wherein the recording layer comprises a compound of formula

A ⁺ (I), preferably a compound of formula

or a mesomeric or tautomeric form thereof, wherein

A i h+ is an organic cation having h quaternary ammonium or phosphonium groups;

Qi is N or CRi5 , Q2 is N or CRi ₆ , Q3, Qs and Q ₇ are each independently of the other CRi ₇ Ri8, O, S or NR ₁₉ , Q ₄ is CR13 or N and Q ₆ is CRi ₄ or N ;

one of Ri and R ₃ is ORi ₇ , OR ₂₀ , SRi ₇ , SR ₂₀ , NRi ₇ Ri ₈ , NRi ₈ R ₂₀ or NR ₂₀ R ₂ I, and the other of Ri and R ₃ is O , S or N R ₂₂ ;

R ₂ , R ₄ , R5, R ₆ , R ₇ , R ₈ , R ₉ , R10, Ri ₂ , Ri ₃ , R14, R15 and Ri ₆ are each independently of all others H, halogen, OR ₂₃ , SR ₂₃ , NRi ₉ R ₂₄ , NRi ₉ COR ₂₅ , NRi ₉ COOR ₂₆ , NRi ₉ CONR ₂₆ R ₂₇ , NRi ₉ CN, OSiRi ₉ R ₂₅ R ₂₈ , CORi ₉ , CRi ₉ OR ₂₅ OR ₂₈ , NO ₂ , CN, COOR ₂₃ , CONR ₂₆ R ₂₇ , SO ₂ Ri ₉ , SO ₂ NR ₂₆ R ₂₇ , SO ₃ R ₂₆ , PO(ORi ₉ )(OR ₂₅ ); Ci-C ₆ alkyl, C ₂ -C ₆ alkenyl, C ₂ -C ₆ alkynyl, C ₃ -C ₆ cycloalkyl, C ₃ -C ₆ cycloalkenyl or C ₂ -C ₅ hetero- cycloalkyl each unsubstituted or mono- or poly-substituted by halogen, OR ₂₃ , SR ₂₃ , NRi ₉ R ₂₄ , NRi ₉ COR ₂₆ , NRi ₉ COOR ₂₆ , NRi ₉ CONR ₂₆ R ₂₇ , NRi ₉ CN, CORi ₉ , CRi ₉ OR ₂₅ OR ₂₈ , NO ₂ , CN, COOR ₂₃ , CONR ₂₆ R ₂₇ and/or SO ₂ R ₂₆ ; or C ₇ -Cnaralkyl, C ₆ -Ci ₀ aryl or Ci-C ₅ heteroaryl each unsubstituted or mono- or poly-substituted by Ci-C ₄ alkyl, halogen, OR ₂₃ , SR ₂₃ , NRi ₉ R ₂₄ , CORi ₉ , NO ₂ , CN and/or COOCi-C ₄ alkyl; or

Ri2 and Ri ₃ or Ri ₂ and Ri ₄ are together in pairs , thus forming a phenyl

ring together with the two adjacent carbons to which they are bound;

Rn is Ci-Ci ₂ alkyl, C ₃ -Ci ₂ cycloalkyl, Ci-Ci ₂ heterocycloalkyl, C ₂ -Ci ₂ alkenyl, C ₃ -Ci ₂ cycloalkenyl, C ₄ -Ci ₂ heterocycloalkenyl, C ₇ -Ci ₂ aralkyl, Ci-C ₉ heteroaryl, C ₂ -Ci iheteroaralkyl, C ₆ -Ci ₂ aryl or Ci-Ci ₂ alkyl interrupted by from one to five non- successive oxygen and/or sulfur atoms and/or by from one to five identical or different groups NRi ₉ , each unsubstituted or mono- or poly-substituted by halogen, OR ₂₃ , SR ₂₃ , NRi ₉ R ₂₄ , NRi ₉ COR ₂₅ , NRi ₉ COOR ₂₆ , NRi ₉ CONR ₂₆ R ₂₇ , NRi ₉ CN, OSiRi ₉ R ₂₅ R ₂₈ , CORi ₉ , CRi ₉ OR ₂₅ OR ₂₈ , NO ₂ , CN, COOR ₂₃ , CONR ₂₆ R ₂₇ , SO ₂ Ri ₉ , SO ₂ NR ₂₆ R ₂₇ , SO ₃ R ₂₆ or PO(ORi ₉ )(OR ₂₅ );

Ri ₇ and Ri ₈ are each independently of the other Ci-Ci ₂ alkyl, C ₂ -Ci ₂ alkenyl, C ₂ -Ci ₂ alkynyl, C ₃ -Ci ₂ cycloalkyl, C ₃ -Ci ₂ cycloalkenyl or C ₂ -Ci iheterocycloalkyl each unsubstituted or mono- or poly-substituted by halogen, OR ₂₃ , SR ₂₃ , NRi ₉ R ₂₄ , NRi ₉ COR ₂₅ , NRi ₉ COOR ₂₆ , NRi ₉ CONR ₂₆ R ₂₇ , NRi ₉ CN, CORi ₉ , CRi ₉ OR ₂₅ OR ₂₈ , NO ₂ , CN, COOR ₂₃ , CONR ₂₆ R ₂₇ and/or SO ₂ R ₂₆ ; or

Ri ₇ and Ri ₈ are together C ₂ -Ci ₂ alkylen, C ₂ -Ci ₂ alkenylen, C ₂ -Ci ₂ cycloalkylen or C ₂ -Ci ₂ cycloalkenylen, one to five non-successive carbon atoms of which can be replaced by oxygen and/or sulfur atoms and/or by identical or different groups NRi ₉ , C ₂ -Ci ₂ alkylen, C ₂ -Ci ₂ alkenylen, C ₂ -Ci ₂ cycloalkylen or C ₂ -Ci ₂ cycloalkenylen being each unsubstituted or mono- or poly-substituted by halogen, OR ₂₃ , SR ₂₃ , NRi ₉ R ₂₄ , NRi ₉ COR ₂₅ , NRi ₉ COOR ₂₃ , NRi ₉ CONR ₂₆ R ₂₇ , NRi ₉ CN, CORi ₉ , CRi ₉ OR ₂₅ OR ₂₈ , NO ₂ , CN, COOR ₂₃ , CONR ₂₆ R ₂₇ and/or SO ₂ R ₂₆ ;

Ri ₉ , R ₂₅ and R ₂₈ are each independently of the others hydrogen; CrC ₄ alkyl, C ₂ -C ₄ alkenyl, C ₂ -C ₄ alkynyl, [C ₂ -C ₃ alkylene-O-] _k -R ₃₃ or [C ₂ -C ₃ alkylene-N R ₃₄ -J _K -R ₃₃ each unsubstituted or mono- or poly-substituted by halogen; or benzyl;

R ₂ O, F*2i and R22 are each independently of the others H, COR24, CONR26R27, CN, SO2NR26R27 or SO2R26, preferably R ₂ o and/or R ₂ i are H and R22 is COR24, CONR ₂₆ R27, CN, SO ₂ NR ₂₆ R27 or SO2R26; or

each R23, independently of any other R23, is R ₂ 4 or R22, preferably H;

R ₂ 4, R2 ₆ and R27 are each independently of the others H; Ci-C ₆ alkyl, C ₂ -C ₆ alkenyl, C ₂ -C ₆ alkynyl, C ₃ -C ₆ cycloalkyl, C ₃ -C ₆ cycloalkenyl or C ₂ -C ₅ heterocycloalkyl each unsubstituted or mono- or poly-substituted by halogen, OR ₂₃ , SR ₂₃ ', NR _I9 R _2S , CN and/or COORi ₉ ; or C ₆ -Ci ₀ aryl, C ₇ -Cnaralkyl or Ci-C ₅ heteroaryl each unsubstituted or mono- or poly-substituted by Ci-C ₄ alkyl, halogen, OR ₂₃ ', SR ₂₃ , NRi ₉ R ₂₅ , CORi ₉ , CRi ₉ OR ₂₅ OR ₂₈ , NO ₂ , CN and/or COOR ₂₈ ;

each R ₂₃ , independently of any other R ₂₃ , is COR ₂₅ , CONR ₂₅ R ₂₈ , CN, SO ₂ NR ₂₅ R ₂₈ or SO ₂ R ₂₈ , preferably H or COR ₂₅ ;

or NRi ₉ R ₂₄ , NRi ₉ R ₂₅ , NR ₂₅ R ₂₈ or NR ₂₆ R ₂ 7 is a five- or six-membered heterocycle which may contain a further N or O atom and which can be mono- or poly- substituted by methyl or ethyl;

R29, R ₃ o, R31 and R ₃₂ are each independently of the others H, Ci-C ₄ alkyl, halogen, OR ₂₃ , SR ₂₃ , NRi ₉ R ₂₄ , CORi ₉ , NO ₂ , CN and/or COOCi-C ₄ alkyl;

R ₃₃ and R ₃₄ are each independently of the other methyl, ethyl, vinyl and/or allyl;

it being possible once or more times radicals of the same or different substituents each selected from the group consisting of Ri, R ₂ , R ₃ , R ₄ , R ₅ , R ₆ , R7, Re, R9, R10, R12, Ri ₃ , Ri4, R15, R16, Ri7, R19, R21 , R22, R2 ₃ , R24, R25, R26, R28, R29, R ₃ o, R31, R32 and R ₃₃ to be bonded to one another in pairs by way of a direct bond or an -O-, -S- or -N(R ₃₄ )- bridge; and

h and k are each independently from the other an integer from 1 to 4.

Substituents, including a plurality of substituents having the same label, are

generally independent from each other.

Alkyl, alkenyl or alkynyl may be straight-chain or branched. Alkenyl is alkyl that is mono- or poly-unsaturated, wherein two or more double bonds may be isolated or conjugated. Alkynyl is alkyl or alkenyl that is doubly-unsaturated one or more times, wherein the triple bonds may be isolated or conjugated with one another or with double bonds. Cycloalkyl or cycloalkenyl is monocyclic or polycyclic alkyl or alkenyl, respectively.

Ci-Ci ₂ Alkyl can therefore be, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, 2-methyl-butyl, n-pentyl, 2-pentyl, 3-pentyl, 2,2-dimethylpropyl, n-hexyl, heptyl, n-octyl, 1 ,1 ,3,3-tetramethylbutyl, 2-ethylhexyl, nonyl, decyl, undecyl or dodecyl.

C ₃ -Ci ₂ Cycloalkyl can therefore be, for example, cyclopropyl, cyclopropyl-methyl, cyclobutyl, cyclopentyl, cyclohexyl, cyclohexyl-methyl, trimethylcyclohexyl, thujyl, norbornyl, bornyl, norcaryl, caryl, menthyl, norpinyl, pinyl, 1-adamantyl or 2-adamantyl.

C ₂ -Ci ₂ Alkenyl is, for example, vinyl, allyl, 2-propen-2-yl, 2-buten-1-yl, 3-buten-1-yl, 1 ,3-butadien-2-yl, 2-penten-1-yl, 3-penten-2-yl, 2-methyl-1-buten-3-yl, 2-methyl- 3-buten-2-yl, 3-methyl-2-buten-1-yl, 1,4-pentadien-3-yl, or any isomer of hexenyl, octenyl, nonenyl, decenyl or dodecenyl.

C ₃ -Ci ₂ Cycloalkenyl is, for example, 2-cyclobuten-1-yl, 2-cyclopenten-1-yl, 2-cyclo- hexen-1-yl, 3-cyclohexen-1-yl, 2,4-cyclohexadien-1-yl, 1-p-menthen-8-yl, 4(10)- thujen-10-yl, 2-norbornen-1-yl, 2,5-norbornadien-1-yl, 7,7-dimethyl-2,4-norcaradien- 3-yl or cam phenyl.

C ₂ -Ci ₂ Alkynyl is, for example, 1-propyn-3-yl, 1-butyn-4-yl, 1-pentyn-5-yl, 2-methyl- 3-butyn-2-yl, 1 ,4-pentadiyn-3-yl, 1 ,3-pentadiyn-5-yl, 1-hexyn-6-yl, cis-3-methyl-2- penten-4-yn-1-yl, trans-3-methyl-2-penten-4-yn-1-yl, 1 ,3-hexadiyn-5-yl, 1-octyn-8- yl, 1-nonyn-9-yl, 1-decyn-10-yl or 1-dodecyn-12-yl.

C ₇ -Ci ₂ Aralkyl is, for example, benzyl, 2-benzyl-2-propyl, β-phenyl-ethyl, 9-fluorenyl, α,α-dimethylbenzyl, ω-phenyl-butyl, ω-phenyl-octyl, ω-phenyl-dodecyl or 3-methyl- S-O'.r.S'.S'-tetramethyl-butyO-benzyl. When C ₇ -d ₂ aralkyl is substituted, both the alkyl moiety and the aryl moiety of the aralkyl group can be substituted, the latter alternative being preferred.

C ₆ -Ci ₂ Aryl is, for example, phenyl, naphthyl or biphenyl, always preferred phenyl.

Halogen is chlorine, bromine, fluorine or iodine, preferably chlorine or bromine on aryl or heteroaryl and fluorine on alkyl.

Ci-Ci ₂ Heteroaryl is an unsaturated or aromatic radical having 4n+2 conjugated π-electrons, for example 2-thienyl, 2-furyl, 1-pyrazolyl, 2-pyridyl, 2-thiazolyl,

2-oxazolyl, 2-imidazolyl, isothiazolyl, triazolyl or any other ring system consisting of thiophene, furan, pyridine, thiazole, oxazole, imidazole, isothiazole, thiadiazole, triazole, pyridine and benzene rings and unsubstituted or substituted by from 1 to 6 ethyl, methyl, ethylene and/or methylene substituents.

Furthermore, aryl and aralkyl can also be aromatic groups bonded to a metal, for example in the form of metallocenes of transition metals known perse, more especially

wherein R ₃₅ is CH ₂ OH, CH ₂ OR ₂₄ or COOR ₂₄ .

C ₃ -C ₁₂ Heterocycloalkyl is an unsaturated or partially unsaturated ring system radical, for example epoxy, oxetan, aziridine; tetrazolyl, pyrrolidyl, piperidyl, piperazinyl, imidazolinyl, pyrazolidinyl, pyrazolinyl, morpholinyl, quinuclidinyl; or some other C ₄ -Ci ₂ heteroaryl that is mono- or poly-hydrogenated.

5- to 12-membered rings are, for example, cyclopentyl, cyclohexyl, cycloheptyl and cyclooctyl, preferably cyclopentyl and especially cyclohexyl.

The quaternary ammonium groups of A ^h+ are preferably heterocyclic, most preferred unsaturated heterocyclic.

Preferably, one of Ri and R ₃ is OH and the other of Ri and R ₃ is O , S , N -CN or N -SO2CF ₃ , especially preferred O . Most preferred, Ri is OH and R ₃ is O .

Either in combination with preferred Ri and/or R ₃ or independently thereof, R2 ₀ is preferably H, unsubstituted or substituted d-Cβalkyl, C ₂ -C ₆ alkenyl, C ₂ -C ₆ alkynyl, C ₃ -C ₆ cycloalkyl, C ₃ -C ₆ cycloalkenyl or C ₂ -C ₅ heterocycloalkyl, or unsubstituted or substituted C ₇ -Cnaralkyl, Cβ-Cioaryl or Ci-C ₅ heteroaryl, especially unsubstituted or monosubstituted d-Cβalkyl or C ₂ -C ₆ alkenyl, in particular methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, allyl, 2-butylen, 3-butylen or isobutylen.

It is especially preferred that, either in combination with preferred Ri, R ₃ and/or R2 ₀ or independently thereof, at least one of R12 and Ri ₄ , especially R12 , is CF ₃ , NO2, CN, COR19, COOR ₂₃ , CRi ₉ OR ₂₅ OR ₂₈ , CONR ₂₆ R27, SO ₂ Ri ₉ , SO ₃ R ₂₃ , SO ₂ NR ₂₆ R ₂ T or PO(ORi ₉ )(OR ₂₅ ), most preferred CF ₃ , NO ₂ , CN, COR19, COOR ₂₃ , SO ₂ Ri ₉ and/or SO ₃ R ₂₃ . Though both Ri ₂ and Ri ₄ may be such preferred groups, preferably only one of them is a preferred group and the other is hydrogen or Ci-C ₄ alkyl, or Ri ₂ and Ri4 are together butadienylen either unsubstituted or substituted, preferably unsubstituted or substituted by CF ₃ , NO ₂ , CN, COR1 ₉ , COOR ₂₃ and/or SO ₃ R ₂₃ .

Preferably, either in combination with preferred Ri, R ₃ , R ₂ o, Ri ₂ and/or R14 or independently thereof, Ri ₃ is H or F, or together with Ri ₂ is butadienylen either unsubstituted or substituted, preferably unsubstituted or substituted by one or more CrC ₄ alkyl, halogen, OR ₂₃ , SR ₂₃ , NRi ₉ R ₂₅ , CF ₃ , NO ₂ , CN, CORi ₉ , COOR ₂₃ , SO ₂ Ri ₉ and/or SO ₃ R ₂₃ , most preferred unsubstituted butadienylen.

Q ₃ is preferably S or CRi ₇ Ri ₈ , more preferably S in

standing for , and/or CRi ₇ Ri ₈ , in particular C ₃ -C ₆ alkyliden or C ₃ -C ₆ cyclo-

alkyliden, (even more preferably 1-cyclohexyliden or especially 2-butyliden — that is, CR17R18 wherein R ₁₇ and R ₁₈ together = 1 ,5-pentylen or R ₁₇ = methyl / R ₁₈ = ethyl,

respectively), in . Most preferably,

stands for - . Q ₅ and Q ₇ are preferably S. These preferences are independent of the preferred R ₁ , R3, R20, R12, R13 and/or R ₁₄ ; however, the preferences disclosed herebefore for R ₁ , R ₃ , R ₂ o, R12, R13 and/or R ₁₄ are fully applicable with particular benefits in the case of

preferred --<Xu| ¹ , Q ₅ and Q ₇ , too.

The preferences for the cationic and anionic sub-structures contained in formula (I) and/or (II) are independent of each other. However, it is preferable to combine preferred cations with preferred anions.

Further preference is given to compounds of formula (I) or (II) wherein R ₅ is hydrogen, hydroxy, CrC ₄ alkoxy or CrC ₄ alkyl; R ₁₂ is nitro or cyano, preferably nitro; and/or R ₁₉ or R ₂₄ are methyl, ethyl, n-propyl, isopropyl, n-butyl, 2-butyl, isobutyl, tert-butyl, 3-pentyl, n-amyl, tert-amyl, neopentyl, 2,2-dimethyl-but-4-yl, cyclopropyl, cyclopropylmethyl, cyclobutyl, cyclobutylmethyl, cyclopentyl, cyclopentyl methyl or cyclohexyl, each unsubstituted or mono- or poly-substituted by fluorine. R ₁₇ and R ₁₈ are preferably both methyl, both ethyl or R ₁₇ ethyl and R ₁₈ methyl, or both together 1 ,5-pentylen. Alkyl, alkenyl, alkynyl, cycloalkyl and heterocycloalkyl are generally preferably CrC ₄ alkyl, C ₂ -C ₄ alkenyl, C ₂ -C ₄ alkynyl and epoxyalkyl, respectively. All these further preferences are fully applicable with particular benefits in the case of

preferred R ₁ , R ₃ , R ₄ , R ₂₀ , R ₁₂ , R ₁₃ and/or R ₁₄ as well as , Q ₅ and Q ₇ , too.

When R ₁₉ , R ₂₅ and R ₂₈ are bonded to one another in pairs by way of a direct bond

or an -O-, -S- or -NR ₃₄ - bridge, they are preferably so bonded that a five- or six- mem bered ring is formed.

Another aspect of the invention are compounds of formula (I) or (II) wherein two cations or two anions are bridged, for example by way of direct bonds or -O-, -S- or -NR ₃₄ - bridges between any substituents in formula (I) or (II), it being possible oligomers to be formed, which are, of course, also to be regarded as being subjects of the invention. Bridgings by way of N atoms of the cation or anion, either those in the chromophore or those on substituents, are especially advantageous.

Such dimer, trimer or higher oligomer formation is illustrated by the following examples (which are on no account limiting) wherein X and X' independently from each other may be, for example, -CH ₂ -, -CH ₂ -CH ₂ -, -CH ₂ -O-CH ₂ - or -CH ₂ -NH-CH ₂ -:

Of course, in dimers, trimers and oligomers the stoichiometry should be such that the resulting compound of formula (I) or (II) is not charged. Such and similar oligomers are generally prepared unintentionally together with the monomeric compounds, but they can be separated by known methods. The formation of

monomers or oligomers can be favoured by usual means through control of the reaction conditions, in particular the respective concentrations of the reagents and the sequence and speed of addition.

The recording medium according to the invention, in addition to comprising the compounds of formula (I) and/or (II), may additionally comprise salts, for example ammonium chloride, pentadecylammonium chloride, sodium chloride, sodium iodide, sodium sulfate, sodium hydrogen sulfate, sodium methyl sulfate, sodium methylsulfonate, sodium tosylate, sodium acetate, sodium hexafluorophosphate, cobalt(II) acetate or cobalt(II) chloride, the ions of which may, for example, originate from the components used.

Interesting anions of formula (I) or (II) are especially those of formulae

The compounds of formula (I) and (II) are new. Some of their components are known, in particular the styryl cation part, for example from US-6 103 331. The final salts of formula (I) and/or (II) are simply prepared by mixing each a soluble salt of the cation and anion. Hence, the invention also pertains to a compound of formula (I) or a tautomeric or mesomeric form thereof.

The compounds of formula (I) and/or (II) are especially useful in combination with the known dyes such as those mentioned herein below.

The substrate, which acts as support for the layers applied thereto, is advantageously semi-transparent (T > 10%) or preferably transparent (T>90%). The support can be from 0.01 to 10 mm thick, preferably from 0.1 to 5 mm thick.

The recording layer is preferably arranged between the transparent substrate and the reflecting layer. The thickness of the recording layer is from 10 to 1000 nm, preferably from 30 to 300 nm, especially about 80 nm, for example from 60 to 120 nm. The absorption of the recording layer is typically from 0.1 to 1.0 at the absorption maximum. The layer thickness is very especially so chosen in known manner in dependence upon the respective refractive indices in the non-written state and in the written state at the reading wavelength that in the non-written state constructive interference is obtained, but in the written state destructive interference is obtained, or vice versa.

The reflecting layer, the thickness of which can be from 10 to 150 nm, preferably has high reflectivity (R>45%, especially R>60%), coupled with low transparency (T < 10%). In further embodiments, for example in the case of media having a

plurality of recording layers, the reflector layer may likewise be semi-transparent, that is to say may have comparatively high transparency (for example T>50%) and low reflectivity (for example R<30%).

The uppermost layer, for example the reflective layer or the recording layer, depending upon the layer structure, is advantageously additionally provided with a protective layer having a thickness of from 0.1 to 1000 μm, preferably from 0.1 to 50 μm, especially from 0.5 to 15 μm. Such a protective layer can, if desired, serve also as adhesion promoter for a second substrate layer applied thereto, which is preferably from 0.1 to 5 mm thick and consists of the same material as the support substrate.

The reflectivity of the entire recording medium is preferably at least 15%, especially at least 40%.

The main features of the recording layer according to the invention are the very high initial reflectivity in the said wavelength range of the laser diodes, which can be modified with great sensitivity; the high refractive index; the especially narrow absorption band in the solid state; the good uniformity of the script width at different pulse durations; as well the good light stability and the good solubility in polar solvents.

The recording medium according to the invention is neither writable nor readable using the infra-red laser diodes of customary CD apparatus in accordance with the requirements of the Orange Book Standard. As a result, the risk of damage in the event of an erroneous attempt at writing using an apparatus not capable of high resolution is largely averted, which is of advantage. The use of dyes of formula (I) and/or (II) results in advantageously homogeneous, amorphous and low-scatter recording layers having a high refractive index, and the absorption edge is surprisingly especially steep even in the solid phase. Further advantages are high light stability in daylight and under laser radiation of low power density with, at the same time, high sensitivity under laser radiation of high power density, uniform script width, high contrast, and also good thermal stability and storage stability.

At a high recording speed (for example 2*, 4*, 8* or 16*, preferably 8* or 16*, corresponding to a range of about 20 to 60 m s ^"1 ), the results obtained are surprisingly better than with previously known recording media. The marks are more precisely defined relative to the surrounding medium, and thermally induced deformations do not occur. The error rate (BLER) and the statistical variations in mark lengths G'tter) are also low both at normal recording speed and at elevated recording speed, so that an error-free recording and playback can be achieved over a wide range of speeds. There are virtually no rejects even at high recording speed, and the reading of written media is not slowed down by the correction of errors. The advantages are obtained over the entire range from 600 to 700 nm (preferably from 630 to 690 nm), but are especially marked at from 640 to 680 nm, more especially from 650 to 670 nm, particularly at 658 ±5 nm.

Suitable substrates are, for example, glass, minerals, ceramics and thermosetting or thermoplastic plastics. Preferred supports are glass and homo- or co-polymeric plastics. Suitable plastics are, for example, thermoplastic polycarbonates, poly- amides, polyesters, polyacrylates and polymethacrylates, polyurethanes, poly- olefins, polyvinyl chloride, polyvinyl idene fluoride, polyimides, thermosetting polyesters and epoxy resins. The substrate can be in pure form or may also comprise customary additives, for example UV absorbers or dyes, as proposed e.g. in JP 04/167 239 to provide light-stabilisation for the recording layer. In the latter case it may be advantageous for the dye added to the support substrate to have an absorption maximum hypsochromically shifted relative to the dye of the recording layer by at least 10 nm, preferably by at least 20 nm.

The substrate is advantageously transparent over at least a portion of the range from 600 to 700 nm (preferably as indicated above), so that it is permeable to at least 90% of the incident light of the writing or readout wavelength. The substrate has preferably on the coating side a spiral guide groove having a groove depth of from 50 to 500 nm, a groove width of from 0.2 to 0.8 μm and a track pitch between two turns of from 0.4 to 1.6 μm, especially having a groove depth of from 100 to 200 nm, a groove width of from 0.35 ± 0.10 μm and a pitch between two turns of

from 0.6 to 0.8 μm. The recording layer is advantageously of different thickness in and outside the groove, depending upon the depth of the groove; the thickness of the recording layer in the groove is usually about from 2 to 20* greater than outside, typically 5-10 ^χ greater in the groove than outside. The recording layer can also be present exclusively in the groove.

The storage media according to the invention are therefore suitable especially advantageously for the optical recording of DVD media having the currently customary minimum pit length of 0.4 μm and track pitch of 0.74 μm. The increased recording speed relative to known media allows synchronous recording or, for special effects, even accelerated recording of video sequences with excellent image quality.

The recording layer, instead of comprising a single compound of formula (I) and/or (II), may alternatively comprise a mixture of such compounds having, for example, 2, 3, 4 or 5 azo dyes according to the invention. By the use of mixtures, for example mixtures of isomers or homologues as well as mixtures of different structures, often the solubility can be increased and/or the amorphous content improved. If desired, mixtures of ion pair compounds may have different anions, different cations or both different anions and different cations.

It is also judicious to use the instant compounds of formula (I) and/or (II) in admixtures with one or more salts of the cation of formula (I) and/or (II) with a suitable inorganic, organic or organometallic anion, and/or with one or more salts of the anion of formula (I) and/or (II) with a proton, a suitable metal, ammonium or phosphonium cation or a positively charged organic or organometallic chromophore. In many cases, the optical properties still remain satisfactory while the solubility and amorphicity of the solid layer can be improved. Compounds of formula (II) provide a particular benefit.

Suitable anions are, for example, hydroxide, oxide, fluoride, chloride, bromide, iodide, perchlorate, periodate, carbonate, hydrogen carbonate, sulfate, hydrogen sulfate, phosphate, hydrogen phosphate, dihydrogen phosphate, tetrafluoroborate,

hexafluoroantimonate, acetate, oxalate, methanesulfonate, trifluoromethane- sulfonate, tosylate, methyl sulfate, phenolate, benzoate or a negatively charged metal complex.

Metal, ammonium or phosphonium cations are, for example, Ca ²⁺ , Co ²⁺ , Co ³⁺ , Cr ³⁺ , Cu ²⁺ , Fe ²⁺ , Fe ³⁺ , K ⁺ , La ³⁺ , Li ⁺ , Mg ²⁺ , Na ⁺ , Ni ²⁺ , Sn ²⁺ , Zn ²⁺ , methylammonium, ethylammonium, pentadecylammonium, isopropylammonium, dicyclohexyl- ammonium, tetramethylammonium, tetraethylammonium, tetrabutylammonium, benzyltrimethylammonium, benzyltriethylammonium, methyltrioctylammonium, tridodecylmethylammonium, tetrabutylphosphonium, tetraphenylphosphonium, butyltriphenylphosphonium or ethyltriphenylphosphonium, or protonated Primene 81 R™ or Rosin Amine D™. Preference is given to H, Na ⁺ , K ⁺ , NH ₄ ⁺ , primary, secondary, tertiary or quaternary ammonium and also to cationic chromophores, especially those mentioned below, as well as cations of the additional chromophores mentioned below (obtainable for example through quaternisation of N). Other metal cations, such as those disclosed hereafter for M-i, are also suitable.

As positively charged organic chromophores there may be used any cations that absorb in the range of from 300 to 1500 nm, especially in the range of from 300 to 800 nm. The person skilled in the art will preferably select especially chromophore cations that have already been previously proposed for use in optical information media, for example cyanine, xanthene, dipyrromethene, styryl, triphenylmethine, azo, metal complex, quinone diimmonium, bipyridinium and other cations. Cyanine, xanthene (for example those of US-5 851 621 , WO-03/098617 or WO-03/098618), dipyrromethene and azo metal complex cations are preferred. Further chromophores suitable for use in cationic form are known from WO-01 /75873, but those examples are on no account to be regarded as a limiting selection.

It has been found that the instant compounds of formulae (I) and/or (II) are especially preferably used in combination with metal complexes, thus providing surprising advantages with respect to the optical properties and sensitivity to the laser recording wavelength while getting good light stability. The instant compounds of formula (I) and/or (II) are most suitably used in optical recording media together

with one or more metal complexes, in a weight ratio of from 5 : 95 to 95 : 5, preferably from 10 : 90 to 90 : 10, especially preferably from 30 : 70 to 70 : 30, it being possible further components comprising metal and/or not comprising metals to be present as well. Preferably, the metal complexes to be combined with the compounds of formulae (I) and/or (II) have a solid state absorption maximum in the spectral range of from 520 to 620 nm.

Most preferred metal complexes to be used in combination with the instant compounds are those of PCT/EP2005/053215 (the contents of which are included herein by reference) of general formula:

(HI), wherein

G ₃ , R36, R37, R38 and R39 independently from Gi, R ₂ , R3, R4 and R ₅ have the same definition as Gi, R ₂ , R ₃ , R4 and R ₅ , respectively, and Mi is a cation in the oxidation state +3, a hydroxy or halogen metal cation wherein the metal is in the oxidation state +4, or an oxo metal cation wherein the metal is in the oxidation state +5, of an at least trivalent metal of groups 3 to 15 (formerly groups IIIA to VB), preferably Al ³⁺ , As ³⁺ , Au ³⁺ , Bi ³⁺ , Ce ³⁺ , Co ³⁺ , Cr ³⁺ , Dy ³⁺ , Er ³⁺ , Eu ³⁺ , Fe ³⁺ , Gd ³⁺ , Ho ³⁺ , Ir ³⁺ , La ³⁺ , Lu ³⁺ , Mn ³⁺ , Mo ³⁺ , Nb ³⁺ , Nd ³⁺ , Pm ³⁺ , Pr ³⁺ , Rh ³⁺ , Ru ³⁺ , Sb ³⁺ , Sc ³⁺ , Sm ³⁺ , Ta ³⁺ , Tb ³⁺ , Ti ³⁺ , [TiCI] ³⁺ , [TiOH] ³⁺ , Tm ³⁺ , V ³⁺ , [VO] ³⁺ , W ³⁺ , Y ³⁺ , Yb ³⁺ , [ZrCI] ³⁺ or [ZrOH] ³⁺ , most preferred Co ³⁺ or Cr ³⁺ .

For a further increase in stability it is also possible, if desired, to add known stabilisers in customary amounts, for example a nickel dithiolate described in JP 04/025 493 as light stabiliser.

The recording layer comprises a compound of formula (I) and/or (II) or a mixture of such compounds advantageously in an amount sufficient to have a substantial influence on the refractive index, for example at least 5% by weight, preferably at least 10% by weight, especially at least 20% by weight, based on the total recording layer. In combination with other recording dyes, in particular metal complex dyes, the amount of compound of formula (I) is preferably from 10 to 70% by weight, especially from 20 to 60% by weight, based on the total recording layer. The recording layer can especially valuably comprise a compound of formula (I) or (II) or a mixture of a plurality of such compounds as one component, or may also consist exclusively or substantially of one or more compounds of formula (I) and/or (II).

Further customary constituents are possible, for example other chromophores (for example those having an absorption maximum at from 300 to 1000 nm), UV absorbers and/or other stabilisers, ¹ O ₂ -, triplet- or luminescence-quenchers, melting-point reducers, decomposition accelerators or any other additives that have already been described in optical recording media, for example film-formers.

When the recording layer comprises further chromophores, such chromophores may in principle be any dyes that can be decomposed or modified by the laser radiation during the recording, or they may be inert towards the laser radiation. When the further chromophores are decomposed or modified by the laser radiation, this can take place directly by absorption of the laser radiation or can be induced indirectly by the decomposition of the compounds of formula (I) and/or (II) according to the invention, for example thermally.

Naturally, further chromophores or coloured stabilisers may influence the optical properties of the recording layer. It is therefore preferable to use further chromophores or coloured stabilisers, the optical properties of which conform as far as possible to, or are as different as possible from, those of the compounds of formula (I) and/or (II) or the amount of further chromophores is kept small.

Further chromophores exhibiting optical properties and/or behaviour in respect of

laser radiation similar to the compounds of formula (I) and/or (II) can for example be used, such as known recording agents, the performance of which is commonly synergistically enhanced or heightened by the compounds of formula (I) and/or (II).

When further chromophores or coloured stabilisers having optical properties that are as different as possible from those of compounds of formula (I) or (II) are used, they advantageously have an absorption maximum that is hypsochromically or bathochromically shifted relative to the dye of formula (I) or (II). In that case the absorption maxima are preferably at least 50 nm, especially at least 100 nm, apart. Examples thereof are UV absorbers that are hypsochromic to the dye of formula (I) or (II) or coloured stabilisers that are bathochromic to the dye of formula (I) or (II) and have absorption maxima lying, for example, in the NIR or IR range. Other dyes can also be added for the purpose of colour-coded identification, colour-masking ("diamond dyes") or enhancing the aesthetic appearance of the recording layer. In all those cases, the behaviour of the further chromophores or coloured stabilisers towards light and laser radiation should preferably be as inert as possible.

When another dye is added in order to modify the optical properties of the compounds of formula (I) and/or (II) the amount thereof is dependent upon the optical properties to be achieved. The person skilled in the art will find little difficulty in varying the ratio of additional dye to compound of formula (I) and/or (II) until he obtains the desired result.

When chromophores or coloured stabilisers are used for other purposes, the amount thereof should preferably be small so that their contribution to the total absorption of the recording layer in the range of from 600 to 700 nm is a maximum of 20%, preferably a maximum of 10%. In such a case, the amount of additional dye or stabiliser is advantageously a maximum of 50% by weight, preferably a maximum of 10% by weight, based on the recording layer.

Further chromophores which can optionally be used in the recording layer in addition to the compounds of formula (I) and/or (II) are, for example, cyanines also including zwitterions (EP-A-1 464678) and metal complexes thereof

(US-5 958 650), oxonol dyes (EP-A-833 314), azo dyes and azo metal complexes (JP-A-11/028865), phthalocyanines (EP-A-232 427, EP-A-337 209, EP-A-373 643, EP-A-463 550, EP-A-492 508, EP-A-509 423, EP-A-511 590, EP-A-513 370, EP-A-514 799, EP-A-518 213, EP-A-519 419, EP-A-519 423, EP-A-575 816, EP-A-600427, EP-A-676 751 , EP-A-712 904, WO-98/14520, WO-00/09522, CH-693/01), porphyrins and azaporphyrins (EP-A-822 546, US-5 998 093), dipyrromethene dyes and metal chelate compounds thereof (EP-A-822 544, EP-A-903 733), xanthene dyes and metal complex salts thereof (US-5 851 621) or quadratic acid compounds (EP-A-568 877), or oxazines, dioxazines, diazastyryls, formazans, anthraquinones or phenothiazines; this list is on no account exhaustive and the person skilled in the art will interpret the list as including further known dyes.

Especially preferred additional compounds are metal complexes, either such known as recording dyes or also as stabilisers or other additives. Most suitable metal complex dyes to be used in combination with the compounds of formula (I) and/or (II) are metal complexes having a solid state absorption maximum in the range of from 520 to 620 nm.

Stabilisers or fluorescence-quenchers are, for example, metal complexes of N- or S-containing enolates, phenolates, bisphenolates, thiolates or bisthiolates or of azo, azomethine orformazan dyes, such as ^® lrgalan Bordeaux EL (Ciba Specialty Chemicals Inc.), ^® Cibafast N3 (Ciba Specialty Chemicals Inc.) or similar compounds, hindered phenols and derivatives thereof (optionally also as anions X ^" ), such as ^® Cibafast AO (Ciba Specialty Chemicals Inc.), 7,7',8,8 ^l -tetracyanoquino- dimethane (TCNQ) and compounds thereof (optionally as an anion of a charge transfer complex), hydroxyphenyl-triazoles or -triazines or other UV absorbers, such as ^® Cibafast W or ^® Cibafast P (Ciba Specialty Chemicals Inc.) or hindered amines (TEMPO or HALS, also as nitroxides or NOR-HALS, optionally also as anions X ^~ ).

Many such structures are known, some of them also in connection with optical recording media, for example from US-5,219,707, JP-A-06/199045, JP-A-07/76169

or JP-A-07/262604. They may be, for example, salts of the metal complex anions disclosed above with any desired cations, for example the cations disclosed above.

Also suitable are neutral metal complexes, for example those metal complexes disclosed in EP 0 822 544, EP 0 844 243, EP 0 903 733, EP 0 996 123, EP 1 056 078, EP 1 130 584 or US 6 162 520, for example

and other known metal complexes, illustrated, for example, by the compounds of formulae

Further suitable additives are organometallic compounds, such as for example ferrocenes, for example those of EP-A-O 600427 or US-A-2003/0224293, which provide some stability while controlling the decomposition temperature.

Especially preferred additional compounds are metal complexes and organometallic compounds, either such known as recording dyes or also as stabilisers or other additives, including in particular all metal complexes disclosed herein before or disclosed in the prior art referred to herein before.

The person skilled in the art will know from other optical information media, or will easily identify, which additives in which concentration are particularly well suited to which purpose. Suitable concentrations of additives are, for example, from 0.001 to 1000% by weight, preferably from 1 to 50% by weight, based on the recording medium of formula (I). This range is also valid for the compounds of formula (II).

The recording medium according to the invention, in addition to comprising the compounds of formula (I) and/or (II) may additionally comprise salts, the ions of which may originate, for example, from the components used, such as those

mentioned above. If present, the additional salts are preferably present in amounts of up to 20% by weight, based on the total weight of the recording layer.

Reflecting materials suitable for the reflective layer include especially metals, which provide good reflection of the laser radiation used for recording and playback, for example the metals of Groups 3- 12, 13, 14 and 15 of the Periodic Table of the Chemical Elements. Ag, Al, Au, Bi, Cd, Ce, Co, Cr, Cu, Dy, Er, Eu, Fe, Gd, Hf, Hg, Ho, In, Ir, La, Lu, Mo, Nb, Nd, Ni, Os, Pb, Pd, Pm, Pr, Pt, Rh, Ru, Sb, Sc, Sm, Sn, Ta, Tb, Ti, Tm, V, W, Y, Yb, Zn and Zr and alloys thereof are especially suitable. Special preference is given to a reflective layer of aluminium, silver, copper, gold or an alloy thereof, on account of its high reflectivity and ease of production. It is suitable to check the compatibility of the reflecting layer with the recording layer compound, which is sometimes borderline at higher temperatures in a moist environment, depending on the chemical structure of the quinoid anion of the recording layer compound and the reflective layer's metal (potential redox reaction).

Materials suitable for the protective layer include chiefly plastics, which are applied in a thin layer to the support or to the uppermost layer either directly or with the aid of adhesive layers. It is advantageous to select mechanically and thermally stable plastics having good surface properties, which may be modified further, for example written on. The plastics may be thermosetting plastics or thermoplastic plastics. Preference is given to radiation-cured (e.g using UV radiation) protective layers, which are particularly simple and economical to produce. A wide variety of radiation-curable materials is known. Examples of radiation-curable monomers and oligomers are acrylates and methacrylates of diols, triols and tetrols, polyimides of aromatic tetracarboxylic acids and aromatic diamines having Ci-C ₄ alkyl groups in at least two ortho-positions of the amino groups, and oligomers having dialkyl- maleinimidyl groups, e.g. dimethylmaleinimidyl groups.

The recording media according to the invention may also have additional layers, for example interference layers. It is also possible to construct recording media having a plurality of (for example two, three, four or five) recording layers. The structure and the use of such materials are known to the person skilled in the art (dual layer

media are described more in detail below). Where present, interference layers are preferably arranged between the recording layer and the reflecting layer and/or between the recording layer and the substrate and consist of a dielectric material, for example as described in EP 0353393 of TiO ₂ , Si ₃ N ₄ , ZnS or silicone resins.

The recording media according to the invention can be produced by processes known per se, it being possible for various methods of coating to be employed depending upon the materials used and their function.

Suitable coating methods are, for example, immersion, pouring, brush-coating, blade-application and spin-coating, as well as vapour-deposition methods carried out under a high vacuum. When, for example, pouring methods are used, solutions in organic solvents are generally employed. When solvents are employed, care should be taken that the supports used are not sensitive to those solvents. Suitable coating methods and solvents are described, for example, in EP-A-401 791.

The recording layer is applied preferably by the application of a dye solution by spin-coating, solvents that have proved satisfactory being especially alcohols, e.g. 2-methoxyethanol, n-propanol, isopropanol, isobutanol, n-butanol, 1-methoxy-2- propanol, amyl alcohol or 3-methyl-1-butanol, or preferably fluorinated alcohols, for example 2,2,2-trifluoroethanol or 2,2,3,3-tetrafluoro-1-propanol, and mixtures thereof. It will be understood that other solvents or solvent mixtures can also be used, for example those solvent mixtures described in EP-A-O 511 598 and EP-A-O 833316. Ethers (dibutyl ether), ketones (2,6-dimethyl-4-heptanone, 5-methyl-2-hexanone), esters (e.g. the lactic acid esters known from WO-03/098617) or saturated or unsaturated hydrocarbons (toluene, xylene or as disclosed in WO-03/034146 tert-butyl-benzene and similar compounds) can also be used, optionally also in the form of mixtures (e.g. dibutyl ether / 2,6-dimethyl- 4-heptanone) or mixed components.

The person skilled in the art of spin-coating will in general routinely try all the solvents with which he is familiar, as well as binary and ternary mixtures thereof, in order to discover the solvents or solvent mixtures which result in a high-quality and,

at the same time, cost-effective recording layer containing the solid components of his choice. Known methods of process engineering can also be employed in such optimisation procedures, so that the number of experiments to be carried out can be kept to a minimum.

The invention therefore relates also to a method of producing an optical recording medium, wherein a solution of a compound of formula (I) or (II) in an organic solvent is applied to a substrate having depressions. The application is preferably carried out by spin-coating.

The application of the metallic reflective layer is preferably effected by sputtering, vapour-deposition in vacuo or by chemical vapour deposition (CVD). The sputtering technique is especially preferred for the application of the metallic reflective layer on account of the high degree of adhesion to the support. Such techniques are known and are described in specialist literature (e.g. J. L. Vossen and W. Kern, "Thin Film Processes", Academic Press, 1978).

The structure of the recording medium according to the invention is governed primarily by the readout method; known function principles include the measurement of the change in transmission or, preferably, reflection, but it is also known, for example, to measure the fluorescence instead of the transmission or reflection.

When the recording material is structured for a change in reflection, the following structures, for example, can be used: transparent support / recording layer

(optionally multilayered) / reflective layer and, if expedient, protective layer (not necessarily transparent); or support (not necessarily transparent) / reflective layer / recording layer and, if expedient, transparent protective layer. In the first case, the light is incident from the support side, whereas in the latter case the radiation is incident from the recording layer side or, where applicable, from the protective layer side. In both cases the light detector is located on the same side as the light source. The first-mentioned structure of the recording material to be used according to the invention is generally preferred.

In particular, a dual layer disk where both recording layers can be recorded and read from the same side can be used: for example DVD+R Dual Layer or DVD-R Dual Layer featuring both 8.5GB/side.

One way to manufacture such dual layer media called "2P Process" uses the following embodiment: transparent substrate / recording material / semi-reflective layer / spacer layer applied by spin-coating and cured through a transparent stamper / second recording layer / reflective layer / adhesive layer / second half disk. Intermediate protective layers can be introduced when required.

Another way to manufacture dual layer media called "inverted stack" consists of making on one hand a half-disk with the following embodiment: transparent substrate / recording material / semi-reflective layer and on the other hand another half-disk with an inverted layer sequence: substrate / reflective layer / recording materials. The two half disks are then bonded together with an adhesive layer so that the two substrates form the two sides of the final disk. Intermediate protective layers can be introduced at various places when required, for example between the recording material and the adhesive layer. Such technique is described in WO-04/021 336 and in WO-04/042717.

Of course, similar or analogue techniques can be used for media with a higher number of recording layers, too.

When the recording material is structured for a change in light transmission, the following different structure, for example, comes into consideration: transparent support / recording layer (optionally multilayered) and, if expedient, transparent protective layer. The light for recording and for readout can be incident either from the support side or the recording layer side or, where applicable, the protective layer side, the light detector in this case always being located on the opposite side.

Suitable lasers are those having a wavelength of from 600 to 700 nm, for example commercially available lasers having a wavelength of 602, 612, 633, 635, 647, 650, 670 or 680 nm, especially semi-conductor lasers, such as GaAsAI, InGaAIP or

GaAs laser diodes having a wavelength especially of about 635, 650 or 658 nm. The recording is effected, for example, point for point in a manner known perse, by modulating the laser in accordance with the mark lengths and focussing its radiation onto the recording layer. It is known from the specialist literature that other methods are currently being developed which may also be suitable for use.

The method according to the invention allows the storage of information with great reliability and stability, distinguished by very good mechanical and thermal stability and by high light stability and by sharp pit boundary zones. Special advantages include the high contrast, the low jitter and the surprisingly high signal/noise ratio, so that excellent readout is achieved. The high storage capacity is especially valuable in the field of video and multimedia.

The readout of information is carried out according to methods known per se by registering the change in absorption or reflection using laser radiation, for example as described in "CD-Player und R-DAT Recorder" (Claus Biaesch-Wiepke, Vogel Buchverlag, Wurzburg 1992).

The information-containing medium according to the invention is especially an optical information material of the WORM type. It can be used, for example, as a playable DVD (digital versatile disk), as storage material for a computer or as an identification and security card or for the production of diffractive optical elements, for example holograms.

The invention accordingly relates also to a method for the optical recording, storage and playback of information, wherein a recording medium according to the invention is used. The recording and/or the playback advantageously take place in a wavelength range of from 600 to 700 nm, preferably as already indicated.

The following Examples illustrate the invention in greater detail (all percentages are by weight, unless otherwise indicated):

Example 1 : 60.0 g of 97% 2-amino-5-nitrothiazole are dissolved, with stirring, in 880 ml of 50% (vol.) sulfuric acid at 23°C. The light-brown solution is cooled to -10 ⁰ C. In the course of 40 minutes, 100 ml of 4N aqueous sodium nitrite solution are added. The now dark blue-green solution is stirred at from -10 to -8°C for a further 15 minutes. During that time, 48 g of resorcinol are dissolved in 400 ml of ethanol and cooled to -10 to -15°C. The resulting solution is then added slowly to the diazonium solution. Immediately a thick, dark red precipitate is formed and the temperature rises to about 0 ⁰ C. The reaction mixture is then stirred for a further 2 hours at from 0 to 5°C, diluted with 500 ml of water and filtered with suction. The suction-filtered material is washed with 4 liters of water and dried for 24 hours at 60 ⁰ C /10 ³ Pa, yielding 78 g of red-brown product of formula:

.

¹ H-NMR [ppm]: 8.87 (s, H _a ); 7.71 /7.74 (d, H _d ); 6.49/6.52 (d, H _c ); 6.46 (s, H _b ).

Example 2: 33.3 g of the compound according to example 1 are dissolved, with stirring, in 550 ml of methanol at 23°C. To the red suspension, 10.25 g of sodium acetate are added. The now violet solution is stirred at room temperature for 3 hours. The solution is filtered with suction, evaporated under vacuum yielding after drying for 12 hours at 50 ⁰ C / 10 ³ Pa 30.76 g of a black powder of formula:

¹ H-NMR [ppm]: 8.45 (s, H _a ); 7.04/7.01 (d, H _d ); 6.16/6.13 (d, H _c ); 5.53/5.52 (d, H _b ).

Example 3: 25 ml of 98% sulfuric acid are dissolved in 260 ml of ethanol under stirring, with some cooling in order to keep a temperature close to 25°C. 28.1 g of phenylhydrazine hydrochloride are added, followed by 38.3 ml of 3-methyl-2- pentanone. The reaction media is then stirred at 75°C for 3 h. After cooling to 23°C,

some ethanol is evaporated under reduced pressure, and 200 ml of 5% aqueous NaOH solution are slowly added. The aqueous phase is extracted with ethyl acetate, and this organic phase is evaporated under reduced pressure to 41.8 g of brown resin. The product of the following formula is used crude for the next step:

¹ H-NMR [ppm]: 7.43 / 7.40 (d, H _a ); 7.34 / 7.33 (d, H _d ); 7.33-7.31 (dd, H _b );

7.16-7,14 (dd, H _c ); 2.15 (s, 3H _e ); 1.98-1.69 (m, 2H _f ); 1.21 (s, 3H _g ); 0.26 (t, 3H _h ).

Example 4: The crude material according to example 3 is dissolved in 150 ml of chloroform, and 20 ml of methyliodide are added. Then, the reaction medium is heated to reflux for 4 hours. It is then cooled to 0 ⁰ C and filtrated at this temperature. The solid obtained is washed with cold acetone, yielding 45 g of a beige compound of formula:

¹ H-NMR [ppm]: 7.97-7.91 (dd, H _a ); 7.82-7.76 (d, H _d ); 7.69-7.61 (m, H _b and H _c );

4.03 (s, 3Hi); 2,80 (s, 3H _e ); 2.28-2.03 (m, 2H _f ); 1.53 (s, 3H _g );

Example 5: 8 g of the compound according to example 4 are dissolved in 200 ml of methanol. 4.8 g of 4-diethylamino-salicylaldehyde are added. The solution is refluxed for 4 hours and stirred for 18 hours at room temperature. The solution is adjusted to a volume of 220 ml and used directly in example 6. An analytical sample is evaporated under reduced pressure to yield a dark-violet crude compound of formula:

¹ H-NMR [ppm]: 11.02 (br. S, OH); 8.42 / 8.37 (d, 1 H); 7.98 / 7.95 (d, 1 H); 7.68-7.61 (m, 2H); 7.55-7.50 (dd, 1 H); 7.44-7.39 (dd, 1 H); 7.23 / 7.18 (d, 1 H); 6.55-6.51 (dd, 1 H); 6.23 / 6.22 (d, 1H); 3.86 (s, 3H); 3.51-3.41 (m, 4H); 3.35 (s, 3H); 2.40-2.18 (m, 2H);

1.69 (s, 3H); 1.17 (t, 6H); 0.34 (t, 3H).

Example 6 (synthesis of salt): 0.3 g of the product according to example 2 is added to 20 ml of methanol at 23°C. 8.8 ml of the solution of example 5 corresponding to 0.5 g of pure compound are added and the resulting solution is stirred for 2 h at 23°C, thus giving a violet suspension. 15 ml of water are added to the suspension and the product is filtered with suction through a Buchner filter and washed with a 1 :1 mixture of methanol and water. Drying at 50 ⁰ C/ 10 ³ Pa yields 0.24 g of an almost black product of formula:

0.16 g of this product are added to 8 ml of 2,2,3, 3-tetrafluoropropanol and sonicated in for 10 minutes. After standing for 2 days at ~23°C, the solution is filtered through a 0.2 μm Teflon™ filter. The dye solution is then applied at 250 rev/min to a 1.2 mm thick, planar polycarbonate disc (diameter 120 mm) and the speed of rotation is increased to 1200 rev/min so that the excess of solution is spun off and a uniform solid layer is formed. After drying, the layer thickness and the complex refractive index of the solid layer are determined by means of spectral transmission and reflection measurements using an optical measuring system (ETA-RT™, Steag ETA-Optik GmbH). The photostability is determined with a calibrated xenon lamp (Hanau), the relative decrease in absorption -D ₂₄ being

measured after 24 hours' irradiation.

Example 7: The compound of formula

is prepared according to example 88 of PCT/EP2005/053215, coated onto a disk and measured according to the method of example 6.

Example 8: 0.08 g of the compound according to example 6 and 0.08 g of the compound of example 7 are added to 8 ml of 2,2,3, 3-tetrafluoropropanol and sonicated in for 10 minutes. After standing for 2 days at ~23°C, the solution is filtered through a 0.2 μm Teflon™ filter. The dye solution is then applied onto a disk and measured according to the method of examples 6 and 7.

The data show that the compounds of formula (II) are highly suitable as optical

recording dyes. In combination with a metal complex, the λ _max of the mixture is advantageously shifted to the wavelength of the compound of formula (II), however with n ₆ 5β of the metal complex and a light stability even better than the pure metal complex.

Example 9: 7.2 g of the compound according to example 2 are dissolved in 180 ml of methanol. 5.5 g of tetramethyl ammonium chloride are added. The solution is stirred at 23°C for 16 hours. The solution is then evaporated at 45°C under reduced pressure until precipitation occurs, then cooled down to 20 ⁰ C. The suspension is filtered with suction through a Buchner filter and washed off with methanol. Drying at 50 ⁰ C / 10 ³ Pa yields 4.4 g of a black product of formula

Example 10: 0.1 g of the compound according to example 9 and 0.9 g of the compound according to example 7 are dissolved together in 99 g of 2,2,3, 3-tetrafluoro- propanol and filtered through a 0.2 μm Teflon™ filter. The dye solution is then applied to a 1.2 mm thick, planar polycarbonate disc (diameter 120 mm) at 250 rpm and the speed of rotation is increased to 1200 rpm so that the excess of solution is spun off and a uniform solid layer is formed. After drying, the layer thickness and the complex refractive index of the solid layer are determined by means of spectral transmission and reflection measurements using an optical measuring system (ETA-RT™, Steag ETA-Optik GmbH). At 658 nm, the dye layer has a refractive index n of 2.42 and an extinction coefficient k of 0.07. The photostability is determined with a calibrated xenon lamp (Hanau), the relative decrease in absorption -D ₂₄ after 24 hours' irradiation is 14%.

The same dye solution is then applied at 250 rpm to the surface of a 0.6 mm thick, grooved polycarbonate disc (groove depth 175 nm, groove width 375 nm, track pitch 0.74 mm) having a diameter of 120 mm. The excess of solution is spun off by increasing the speed of rotation. When the solvent is evaporated off, the dye

remains behind in the form of a uniform, amorphous solid layer. Drying is carried out in a circulating-air oven at 70 ⁰ C for 20 minutes. In a vacuum-coating apparatus (Twister™, Balzers Unaxis), a 120 nm thick silver layer is then applied to the recording layer by sputter coating. An adhesive layer of a UV-curable photopolymer (LMD2277™, Vantico/ Huntsman) is then applied thereto by spin-coating, and a second polycarbonate disc (0.6 mm thick, 120 mm diameter) is adhesively bonded thereto. On a commercial test apparatus (ODU-1000™, Pulstec Japan), using a laser diode of wavelength 658 nm and a numerical aperture of 0.65, marks are written into the active layer at speeds of -8.4 m ^■ s ^"1 (8.38 = 2.4 x) and 42 m ^■ s ^"1 (12x). On the same apparatus, the following dynamic parameters are determined: R14H reflectivity, I14/I14H modulation, and data-to-clock (DTC) jitter.

The performance is excellent at both low (2.4 x) and high (12 x) recording speeds.

Example 11 : The same procedure as described in example 10 is applied to the pure compound described in example 7. Discs are made and the following dynamic parameters are determined: R14H reflectivity, I14/I14H modulation, and data-to- clock (DTC) jitter.

Both reflectivity and modulation values are lower than in example 10 while the jitter is identical at high recording speed. The compound of example 9 is synergistically boosting the performance of the compound of example 7.

The instant optical recording media according to above examples are compatible with both DVD+R and DVD-R formats. Excellent performance, both at low (2.4 x) and high (16 *) recording speeds, are obtained in particular with a groove depth of from 150 to 190 nm and a groove width of from 0.35 to 0.40 μm, preferably with a groove depth of from 160 to 180 nm and a groove width of from 0.36 to 0.39 μm, most preferred with a groove depth of from 165 to 175 nm and a groove width of from 0.37 to 0.38 μm; preferably in combination with a groove side wall angle of from 60 to 85°, more preferably from 65 to 80°, most preferred from 70 to 75°.