WO2007090765A2

WO2007090765A2 - High capacity optical storage media comprising organometallic ion pairs

Info

Publication number: WO2007090765A2
Application number: PCT/EP2007/050922
Authority: WO
Inventors: Frédérique Wendeborn; Jean-Marie Adam; Jean-Pierre Bacher; Gisèle BAUDIN; Jean-Luc Birbaum; Jean-Luc Budry; Tobias Hintermann; Yuichi Nishimae; Jitka Brynjolffssen; Suyou Liu
Original assignee: Ciba Holding Inc.
Priority date: 2006-02-09
Filing date: 2007-01-31
Publication date: 2007-08-16
Also published as: WO2007090765A3; TW200805362A

Abstract

The invention , wherein the recording track comprises a compound of formula (I) or a mesomeric or tautomeric form thereof and are each independently of the other, or ; is or C2-C8heteroaryl unsubstituted or mono- or poly-substituted by R47, R48, R49 and/or R50; Q1 and Q6 are each independently of the other O or S; Q2 and Q4 are each independently of the other O, S or NR51; Q3 is N or CR52; Q5 is N, or is CR14 when Q4 is O or S; Q7 is O, S, CR22R23 or NR35; Q8 and Q10 are each independently of the other CR53R54, O, S or NR55; Q9 is CR43 or N; Q11 is CR56 or N; Q12, Q14 and Q16 are each independently of the other CR57R58, O, S or NR51; Q13 and Q15 are each independently of the other CR59 or N. The structures of the cations and the substituents are defined in the description. The invention also pertains to the use of compounds of the formula (I) in optical recording with a blue laser as well as to optical recording processes wherein pits of either lower or higher reflecticity are written on a track comprising compounds of the formula (I). Hence, the invention finally also relates to an optical recording medium comprising a recording dye which is bathochromic as compared with the laser wavelength, on which medium pits of lower reflectivity are written on a higher reflectivity track.

Description

High capacity optical storage media comprising organometallic ion pairs

The invention relates to new optical recording materials that have excellent recording and playback quality especially at a laser wavelength of 350-500 nm (for example HD DVD-R™ or Blu-ray Disc™ standards). Recording and playback can be effected very advantageously with high sensitivity, and the storage density that is achievable is significantly higher than in the case of materials recordable at a higher wavelength, such as around 658 ± 5 nm (DVD-R or DVD+R standards). In addition, the materials according to the invention have very good storage properties before and after recording, even under especially harsh conditions, such as exposure to sunlight or fluorescent lighting, heat and/or high humidity. Their manufacture is simple and readily reproducible using customary coating processes, such as spin-coating.

WO 04 /088649 discloses optical recording media comprising a broad choice of metal complex dyes and recorded with a laser of wavelength around 658 ± 5 nm. However, the examplified dyes are not well suitable for use with a laser beam of short wavelength, such as 405 ± 5 nm.

WO 06/018352 is a patent application according to Art. 54(3) EPC and Rule 64.3 PCT, which is also directed to optical recording media recordable with a laser of wavelength around 658 ± 5 nm (DVD-R or DVD+R).

It has now been found that some selected dyes that are broadly encompassed by WO 04 /088649 or WO 06/018352 are particularly suitable for use at shorter wavelength, when the disk is constructed differently.

EP-1 265233 discloses an optical information medium suitable for recording at 405 nm, which uses a mixture of two dyes, one of which has an absorption of 0.07 at the recording wavelength. Example 1 uses a mixture of a phthalocyanine and an anthraquinone dyes.

US-2002/ 0034605 discloses an optical recording medium wherein the dye absorbs at a wavelength higher than that of the writing light. Cyanine dyes are used for recording at 390-450 nm. US-2004 / 0058274 and WO 02 / 102598 follow the same idea with trimethinecyanine dyes.

EP-1 587092 and EP-1 587093 disclose low to high recording media suitable for use at 405 nm, using for example the coloring matter C (see figure 1 , chemical

formula 1 ) of formula , the

absorption maximum of which is at 542 nm in methanol.

WO 2005 / 123842 discloses the use of particular hemicyanine dyes having inorganic anions in optical recording media suitable for the blue laser range.

However, still none of the prior art propositions leads to fully satisfactory results. Moreover, it is not possible yet to achieve all blue laser standards with the same recording dyes, what would be highly desirable because switching from one recording dye to another implies a lot of development work as well as breakdown time for cleaning the production lines, and each dye must be registered as well as certified for each standard. Working in parallel with two dyes on the same plant is undesirable, too.

A significant improvement has surprisingly now been obtained by using the anions of WO 04 /088649 together with heterocyclic cations which are more hypsochro-

mical than the hitherto proposed ones (such as , the

UV/VIS absorbtion maximum of which is at 555 nm in ethanol). Due to the unique optical properties of the instant compounds, both high to low and low to high recording modes can surprisingly be achieved with the same recording dye, which is hence compatible with both standards.

The invention accordingly relates to an optical recording medium suitable for optical recording with a laser of wavelength below 600 nm, preferably from 350 to 500 nm, comprising a grooved substrate, a reflecting layer and a recording track of width from 100 to 400 nm, preferably from 150 to 250 nm, depth from 10 to 200 nm, preferably from 20 to 90 nm, and pitch from 250 to 430 nm, preferably from 310 to 399.9 nm, wherein the recording track comprises a compound of formula

or a mesomeric or tautomeric form thereof, wherein

Mi is a metal cation in the oxidation state +3, a hydroxy or halogeno metal group wherein the metal is in the oxidation state +4, or an oxo metal group wherein the metal is in the oxidation state +5;

Zi is a cation having n positive charges, the iodide salt of which has an absorption band in the UV-A or visible range, the absorption maximum of which is at a wavelength of from 350 to 550 nm, which cation is selected from the group consisting of cations of the formulae

or or C₂-C₈heteroaryl unsubstituted or mono-

or poly-substituted by R47, R48, R49 and/or R₅o;

Qi and Q₆ are each independently of the other O or S ; Q₂ and Q₄ are each independently of the other O, S or NR51 ; Q3 is N or CR₅₂ ; Qs is N, or is CR14 when Q₄ is O or S ; Q₇ is O, S, CR₂₂R₂₃ or NR35 ; Qs and Q10 are each independently of the other CR53R54, O, S or NR₅₅ ; Qg is CR₄₃ or N ; Qn is CR₅₆ or N ; Qi₂, Q₁₄ and Qi₆ are each independently of the other CR₅₇R₅S, O, S or NR51 ; Q13 and Qi₅ are each independently of the other CR₅₉ or N ;

R₁, R₃, R₄, R5, R7 and R₈ are each independently of the others H, halogen, OR₆O, SR₆₀, NR₄iR₅₅, NR₅₅COR₆I, OSiR₅₅R₆iR₆₂, COR₅₅, CR₅₅OR₆iOR₆₂, NO₂, CN, COOR₆₀, CONR₆₃R₆₄, SO₂R₅₅, SO₂NR₆₃R₆₄, SO₃R₆₃; Ci-C₆alkyl, C₂-C₆alkenyl, C₂-C₆alkynyl, C₃-C₆cycloalkyl, C₃-C₆cycloalkenyl or C₂-C₅heterocycloalkyl each unsubstituted or mono- or poly-substituted by halogen; or C₇-Cnaralkyl, C₆-Ci₀aryl or Ci-C₈heteroaryl each unsubstituted or mono- or poly-substituted by Ci-C₄alkyl, halogen, OR₆₀, SR₆₀, NR₄iR₅₅, COR₅₅, NO₂, CN and/or COOCi-C₄alkyl;

R₂ and/or R₆ are O, S or NR₆₅;

Rg, R10, R₁1 , R₁₂, R₁4, R₁5, R16, R₁7, R18, R38, R39, R40, R44, R45, R46, R47, R48, R49, R50, R52 and R₅₉ are each independently of the other H, halogen, OR₆₆, SR₆₆, NR₅iR₆₇, NR₅iCOR₆₈, NR₅iCOOR₆₉, N R51 CON R₆₉R₇₀, NR₅iCN, OSiR₅iR₆₈R₇i, COR₅I, CR₅iOR₆₈OR₇i, NO₂, CN, COOR₆₆, CONR₆₉R₇₀, SO₂R₅I, SO₂NR₆₉R₇₀,

SO₃R₆₉; Ci-C₆alkyl, C₂-C₆alkenyl, C₂-C₆alkynyl, C₃-C₆cycloalkyl, C₃-C₆cycloalkenyl or C₂-C₅heterocycloalkyl each unsubstituted or mono- or poly-substituted by halogen, OR₆₆, SR₆₆, NR₅iR₆₇, NR₅iCOR₆₈, NR₅iCOOR₆₆, N R₅₁ CON R₆₉R₇₀, NRsiCN, COR₅I, CR₅iOR₆₈OR₇i, NO₂, CN, COOR₆₆, CONR₆₉R₇₀ and/or SO₂R₆₉; or C₇-Ci iaralkyl, C₆-Ci₀aryl or Ci-C₈heteroaryl each unsubstituted or mono- or poly- substituted by Ci-C₄alkyl, halogen, OR₆₆, SR₆₆, NR₅iR₆₇, COR₅i, NO₂, CN and/or COOCi-C₄alkyl;

R₁3 and R35 are independently of each other Ci-C₂oalkyl, C₃-Ci₂cycloalkyl, Ci-Ci₂heterocycloalkyl, C₂-C₂oalkenyl, C₃-Ci₂cycloalkenyl, C₄-Ci₂heterocyclo- alkenyl, C₂-C₂₀alkynyl, C₇-Ci₈aralkyl, Ci-C₉heteroaryl, C₂-Ci₇heteroaralkyl, C₆-Ci₂aryl or Ci-Ci₂alkyl interrupted by from one to five non-successive oxygen and/or sulfur atoms and/or by from one to five identical or different groups NR₅₁ , each unsubstituted or mono- or poly-substituted by halogen, OR₆6, SR₆6, NR51R67, NR₅iCOR₆8, NR₅ICOOR₆₉, N R51 CON R₆₉R₇₀, NR₅iCN, OSiR₅iR₆₈R₇i, COR₅i, CR₅IOR₆₈OR₇I, NO₂, CN, COOR₆₆, CONR₆₉R₇₀, SO₂R₅I, SO₂NR₆₉R₇₀, SO₃R₆₉;

R₁₉, R₂₀ and R₂i are each independently of the other H, halogen, OR₆₆, SR₆₆, OSiR₅I R₆₈R₇I, CR₅I OR₆₈OR₇I; Ci-C₆alkyl, C₂-C₆alkenyl, C₂-C₆alkynyl, C₃-C₆cycloalkyl, C₃-C₆cycloalkenyl or C₂-C₅heterocycloalkyl each unsubstituted or mono- or poly-substituted by halogen, OR₆₆, SR₆₆, NR₅iR₆₇, NR₅iCOR₆₈, NR₅iCOOR₆₆, NR₅I CON R₆₉R₇₀, NR₅iCN, COR₅i, CR₅iOR₆₈OR₇i, NO₂, CN, COOR₆₆, CONR₆₉R₇₀ and/or SO₂R₆₉; or C₇-Cnaralkyl, C₆-Ci₀aryl or Ci-C₈heteroaryl each unsubstituted or mono- or poly-substituted by Ci-C₄alkyl, halogen, OR₆₆, SR₆₆, NR₅iR₆₇, COR_5I and/or COOCi-C₄alkyl;

R₂₂ and R₂₃ are each independently of the other Ci-Ci₂alkyl, C₂-Ci₂alkenyl, C₂-Ci₂alkynyl, C₇-Ci₂aralkyl, C₃-Ci₂cycloalkyl, C₃-Ci₂cycloalkenyl or C₂-Ci ihetero- cycloalkyl each unsubstituted or mono- or poly-substituted by halogen, OR₆₆, SR₆₆, NR_5I R₆₇, NR_5I COR₆₈, N R_5i COOR₆₆, N R_5i CON R₆₉R₇₀, NR₅iCN, COR₅i, CR₅iOR₆₈OR₇i, NO₂, CN, COOR₆₆, CONR₆₉R₇₀ and/or SO₂R₆₉ ;

or R₂₂ and R₂₃ are together C₂-Ci₂alkylen, C₂-Ci₂alkenylen, C₂-Ci₂cycloalkylen or C₂-Ci₂cycloalkenylen, 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

NR_5I , C₂-Ci₂alkylen, C₂-Ci₂alkenylen, C₂-Ci₂cycloalkylen or C₂-Ci₂cycloalkenylen being each unsubstituted or mono- or poly-substituted by halogen, OR₆₆, SR₆₆, NR₅iR₆₇, NR₅iCOR₆₈, NR₅iCOOR₆₆, N R_5i CON R₆₉R₇₀, NR₅iCN, COR₅i, CR₅iOR₆₈OR₇i, NO₂, CN, COOR₆₆, CONR₆₉R₇₀ and/or SO₂R₆₉ ; R24, R25, R27, R28, R29, R30, R31 and R₃2 are each independently of the other H, halogen, COR₅i, NO₂, CN, SO₃R₆9; or Ci-C₆alkyl, C₆-Ci₂aryl, C₇-Ci₂aralkyl each unsubstituted or mono- or poly-substituted by halogen, Ci-C₈alkyl and/or SO3R69;

R₂₆ is halogen, COOR₆₆, CONR₆₉R₇₀; or Ci-C₂₀alkyl, C₇-d₈aralkyl each unsubstituted or mono- or poly-substituted by halogen, Ci-C₈alkyl, COR51, COOR₆₆, CONR₆₉R₇₀, OR₆₆, CN and/or SO₃R₆₉;

R₃₃ is Ci-Ci₂alkyl, C₂-Ci₂alkenyl, C₂-Ci₂alkynyl, C₇-Ci₂aralkyl, C₃-Ci₂cycloalkyl, C₃-Ci₂cycloalkenyl or C₂-Ci iheterocycloalkyl each unsubstituted or mono- or poly- substituted by halogen, OR₆₆, SR₆₆, NR₅iR₆₇, NR₅iCOR₆₈, NR₅iCOOR₆₆, N R51 CON R₆₉R₇₀, NR51CN, COR51, CR₅iOR₆₈OR₇i, NO₂, CN, COOR₆₆, CONR₆₉R₇₀ and/or SO₂R₆₉ ;

or R_H and R₃₃ are together with the nitrogen and the carbon atoms joining them together a 5- or a 6-membered ring;

R₃₄ is H, CH₃ or C₂H₅ each unsubstituted or mono- or poly-substituted by halogen,

R₃₆ and R₃₇ are each independently of the other H; Ci-Ci₂alkyl, C₂-Ci₂alkenyl, C₂-Ci₂alkynyl, C₃-Ci₂cycloalkyl, C₃-Ci₂cycloalkenyl or C₂-Ci iheterocycloalkyl each unsubstituted or mono- or poly-substituted by halogen, OR₆₀, SR₆₀ or NR₄iR₅₅; or C₇-Ci iaralkyl, C₆-Ci₀aryl or Ci-C₈heteroaryl each unsubstituted or mono- or poly- substituted by d-C₄alkyl, halogen, OR₆₀, SR₆₀, NR₄iR₅₅, COR₅₅, NO₂, CN and/or COOCi-C₄alkyl;

R41, R₆₃, R₆₄, Re7, Reg and R₇₀ are each independently of the others H; Ci-C₆alkyl, C₂-C₆alkenyl, C₂-C₆alkynyl, C₃-C₆cycloalkyl, C₃-C₆cycloalkenyl or C₂-C₅hetero- cycloalkyl each unsubstituted or mono- or poly-substituted by halogen, OR₇₂, SR₇₂, NR₅₅R₆₂, CN and/or COOR₅₅; or C₆-Ci₀aryl, C₇-Cnaralkyl or Ci-C₅heteroaryl each unsubstituted or mono- or poly-substituted by Ci-C₄alkyl, halogen, OR₇₂, SR₇₂, NR₅₅R₆I, COR₅₅, CR₅₅OR₆iOR₆₂, NO₂, CN and/or COOR₆₂; or NR₆3R64 and/or NR69R70 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 and/or ethyl;

R42, R43 and R₅6 are each independently of the others H, halogen, OR₆O, SR₆O, NR41R55, NR₅₅COR₆I, NR₅₅COOR₆₃, NR₅₅CONR₆₃R₆₄, NR₅₅CN, OSiR₅₅R₆iR₆₂, COR₅₅, CR₅₅OR₆iOR₆₂, NO₂, CN, COOR₆₀, CONR₆₃R₆₄, SO₂R₅₅, SO₂NR₆₃R₆₄, SO₃R₆₃, PO(OR₅₅)(OR_6I); Ci-C₆alkyl, C₂-C₆alkenyl, C₂-C₆alkynyl, C₃-C₆cycloalkyl, C₃-C₆cycloalkenyl or C₂-C₅heterocycloalkyl each unsubstituted or mono- or poly- substituted by halogen, OR₆₀, SR₆₀, NR₄iR₅₅, NR₅₅COR₆I, NR₅₅COOR₆₀, NR₅₅CONR₆₃R₆₄, NR₅₅CN, COR₅₅, CR₅₅OR₆iOR₆₂, NO₂, CN, COOR₆₀, CONR₆₃R₆₄ and/or SO₂R₆₃; or C₇-Cnaralkyl, C₆-Ci₀aryl or Ci-C₈heteroaryl each unsubstituted or mono- or poly-substituted by Ci-C₄alkyl, halogen, OR₆₀, SR₆₀, NR₄iR₅₅, COR₅₅, NO₂, CN and/or COOCi-C₄alkyl;

or one or more pairs R₉ and R₁₀ , R₁₀ and Rn , Rn and R₁₂ , R14 and R₁₅ , R₁₄ and R₂₀ , RH and R₂i , R₁₅ and R₁₆ , R₁₅ and R19 , R₁₅ and R₂₀ , R₁₆ and R17 , R₁₆ and R₅₂ , Ru and R₁₈ , R17 and R₂₀ , R₁₇ and R₂i , R₁₈ and R₃₃ , R₁₈ and R₅₂ , R₂₀ and R52 , R21 and R₅₂ , R₂₄ and R₂₅ , R₂₇ and R₂₈ , R₂₉ and R₃₀ , R₃₀ and R₃i , R₃i and R₃2 , R₃9 and R₄₀ , R42 and R₄₃ , R42 and R₅₆ , R₄₄ and R₅₉ , and/or R₄₇ and R₄₈ , are independently from all other of these pairs together a bivalent group of the formula

, thus forming a

benzene, cyclohexene, cyclohexadiene, cyclopentadiene or cyclopentene ring with the two adjacent carbons to which they are bound;

R51, R55, Rei, Re2, Res and R₇i are each independently of the others hydrogen, benzyl; or Ci-C₄alkyl, C₂-C₄alkenyl, C₂-C₄alkynyl, [C₂-C₃alkylen-O-]_k-R₈i or [C₂-C₃alkylen-NR₈₂-]k-R8i each unsubstituted or mono- or poly-substituted by halogen; or NR51R67, NR51R68, NR41R55 and/or NR55R61 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 and/or ethyl;

R53, R54, R57 and R₅S are each independently of the other Ci-Ci₂alkyl, C₂-Ci₂alkenyl, C₂-Ci₂alkynyl, C₇-Ci₂aralkyl, C₃-Ci₂cycloalkyl, C₃-Ci₂cycloalkenyl or C₂-Ci iheterocycloalkyl each unsubstituted or mono- or poly-substituted by halogen, OR₆₀, SR₆₀, NR41R55, NR₅₅COR₆I, NR₅₅COOR₆₀, NR₅₅CONR₆₃R₆₄, NR₅₅CN, COR₅₅, CR₅₅OR₆iOR₆₂, NO₂, CN, COOR₆₀, CONR₆₃R₆₄ and/or SO₂R₆₃ ;

or R₅₃ and R₅₄ and/or R₅₇ and R₅₈ are together as a pair C₂-Ci₂alkylen, C₂-Ci₂alkenylen, C₂-Ci₂cycloalkylen or C₂-Ci₂cycloalkenylen, 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 NR₅₅ , C₂-Ci₂alkylen, C₂-Ci₂alkenylen, C₂-Ci₂cycloalkylen or C₂-Ci₂cycloalkenylen being each unsubstituted or mono- or poly-substituted by halogen, OR₆₀, SR₆₀, NR₄iR₅₅, NR₅₅COR₆I, NR₅₅COOR₆₀, NR₅₅CONR₆₃R₆₄, NR₅₅CN, COR₅₅, CR₅₅OR₆iOR₆₂, NO₂, CN, COOR₆₀, CONR₆₃R₆₄ and/or SO₂R₆₃ ;

each R₆₀ or R₆₆, independently of any other R₆₀ or R₆₆, is R₄₁ or R₆₅ ;

R₆₅ is COR41, COOR41, CONR₆₃R₆₄, CN, SO₂NR₆₃R₆₄ or SO₂R₆₃;

each R₇₂, independently of any other R_72, is independently of the others Ci-C₆alkyl, C₂-C₆alkenyl, C₂-C₆alkynyl, C₃-C₆cycloalkyl, C₃-C₆cycloalkenyl or C₂-C₅hetero- cycloalkyl each unsubstituted or mono- or poly-substituted by halogen, NR₅₅R₆₂, CN and/or COOR₅₅; or C₆-Ci₀aryl, C₇-Ci iaralkyl or Ci-C₅heteroaryl each unsubstituted or mono- or poly-substituted by Ci-C₄alkyl, halogen, NR₅₅R₆I, COR₅₅, CR₅₅OR₆iOR₆₂, NO₂, CN and/or COOR₆₂;

R₇₃, R₇₄, R75 and R₇₆ are each independently of the other H, Ci-C₄alkyl, halogen, OR₆₆, SR₆₆, NR₅iR₆₇, COR_5I, NO₂, CN or COOCi-C₄alkyl;

or one or more pairs R₇₃ and R₇₄, R₇₄ and R₇₅ and/or R₇₅ and R₇₆ are independently from both other pairs together - thus

forming a benzene or a partially or fully saturated 6-membered ring with the two adjacent carbons to which they are bound;

R77, R78, R79 and R₈O are each independently of the other H, Ci-C₄alkyl, halogen, OR₆6 or SR₆6, it being possible R73 to form a 3-, A-, 5- or 6-membered ring with R77, R₇₄ to form a 3-, A-, 5- or 6-membered ring with R₇₈, R₇5 to form a 3-, A-, 5- or 6-membered ring with R₈₀ or R₇₆ to form a 3-, A-, 5- or 6-membered ring with R₇₉; or R₇₃ and R₇₇, R₇₄ and R₇₈, R₇₅ and R₇₉ or R₇₆ and R₈₀ are together NR51, O or S;

R₈i and R₈₂ are each independently of the other methyl, ethyl, vinyl and/or allyl;

R₈₃, R₈₄, Res and R₈₆ are each independently of the other H, Ci-C₄alkyl, halogen, OR₆₆, SR₆₆, NR₅iR₆₇, COR₅I, NO₂, CN or COOCrC₄alkyl;

it being possible once or more times radicals of the same or different substituents each selected from the group consisting of R₁, R₃, R₄, R₅, R₇, R₈, R₉, R10, Rn, R12, R₁₃, R₁₄, R₁₅, R₁₆, R₁₇, R₁₈, R₁₉, R₂₀, R₂₁ , R₂₂, R₂₃, R₂₄, R₂₅, R₂₆, R₂₇, R₂₈, R₂₉, R₃₀, R₃₁ , R₃₂, R₃₄, R₃₅, R₃₈, R₃₉, R₄₀, R₄₁ , R₄₂, R₄₃, R₄₄, R₄₅, R₄₆, R₄₇, R₄₈, R₄₉, R₅₀, R₅₁ ,

R₅₃, R₅₅, R₅₆, R₅₇, R₅₉, R₆₀, R₆₁ , R₆₂, R₆₃, R₆₅, R₆₆, R₆₇, R₆₈, R₆₉, R₇₂, R₇₃, R₇₄, R₇₅,

R₇₆, R₈₁, R₈₃, R₈₄, R₈₅ and R₈₆ to be bonded to one another in pairs by way of a direct bond or an -O-, -S- or -N(R₈₂)- bridge, optionally forming a compound comprising two or three identical or different moieties of formula (I);

k is an integer from 1 , 2, 3 or 4; and n is an integer 1 , 2 or 3.

The recording laser has more preferably a wavelength of from 370 to 450 nm. Especially preferred is within the UV-A range a wavelength of from 370 to 390 nm, especially approximately 380 nm, or especially at the edge of the visible range of from 390 to 430 nm, more preferably approximately 405 ± 5 nm. The UV-A range is from 315 to 400 nm, the visible range from 400 to 700 nm. The absorption maximum of the iodide salt of the cation Zi is preferably at a wavelength of up to 545 nm, more preferably from 350 to 520 nm, especially from 420 to 520 nm. The 315 to 700 nm spectrum is most adequately measured at a concentration of 2 ^■ 10^"4 mol/l in ethanol, or alternatively in dichloromethane if the solubility in ethanol is insufficient, or in N,N-dimethylformamide if the solubilities in both ethanol and dichloromethane are insufficient.

Substituents, including a plurality of substituents having the same label, are generally independent from each other. Preferred are compounds of formula (I), wherein n is 1 , as well as alternatively compounds of formula (I), wherein n is 2 and Zi^π+ consists of two identical or different cations Z/ linked together by way of a direct bond or an -O-, -S- or -N(R₈2)- bridge.

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 Al³⁺, As³⁺, Au³⁺, Bi³⁺, Ce³⁺, Co³⁺, Cr³⁺, Dy³⁺, Er³⁺, Eu³⁺, Fe³⁺, Gd³⁺, Ho³⁺, Ir³⁺, La³⁺, Lu³⁺, Mn³⁺, Mo³⁺, Nb³⁺, Nd³⁺, Pm³⁺, Pr³⁺, Rh³⁺, Ru³⁺, Sb³⁺, Sc³⁺, Sm³⁺, Ta³⁺, Tb³⁺, Ti³⁺, [TiCI]³⁺, [TiOH]³⁺, Tm³⁺, V³⁺, [VO]³⁺, W³⁺, Y³⁺, Yb³⁺, [ZrCI]³⁺ or [ZrOH]³⁺, most preferred Co³⁺ or Cr³⁺.

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-Ci₂Alkyl 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. C₃-Ci₂Cycloalkyl 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.

C₂-Ci₂Alkenyl 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.

C₃-Ci₂Cycloalkenyl 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 camphenyl.

C₂-Ci₂Alkynyl 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.

C₇-Ci₂Aralkyl is, for example, benzyl, 2-benzyl-2-propyl, β-phenyl-ethyl, 9-fluorenyl, α,α-dimethylbenzyl, ω-phenyl-butyl, co-phenyl-octyl, co-phenyl-dodecyl or 3-methyl- δ^rj'^'^'-tetramethyl-butyO-benzyl. When C₇-Ci₂aralkyl is substituted, both the alkyl moiety and the aryl moiety of the aralkyl group can be substituted, the latter alternative being preferred.

C₆-Ci₂Aryl 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.

d-CgHeteroaryl 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-oxa- zolyl, 2-imidazolyl, isothiazolyl, triazolyl, tetrazolyl or any other ring system consis- ting of thiophene, furan, thiazole, oxazole, imidazole, isothiazole, thiadiazole, triazo- Ie, pyridine, pyrazine, pyrimidine, pyridazine and benzene rings and unsubstituted or substituted by from 1 to 6 substituents, for example methyl, ethyl, 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 per se, more

especially

wherein R₈₇ is CH₂OH, CH₂OR₄I or COOR₄L

C₃-Ci₂Heterocycloalkyl 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 C₄-Ci₂heteroaryl that is mono- or poly-hydrogenated.

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

are independently from each other preferably

or . Gi and G₂ are most preferred

identical. Preferably, stands for

wherein CR53R54 ist in particular C3-C₆alkyliden or C3-C₆cycloalkyliden, even more preferably 1 -cyclohexyliden or especially 2-butyliden — that is, wherein R53 and R₅₄ together = 1 ,5-pentylen or R₅3= methyl / R₅₄= ethyl, respectively). Q₈ is preferably S. The quinoid structure with double bonds to R2 and R₆ is of course only one mesomeric form of the compound of formula (I), but it is the most likely structure in view of the spectroscopic data. There may alternatively also be drawn a phenylazo with a single bond to R2 or R₆ and a negative charge on R₂ or R₆, which may further be protonated through tautomery. Nevertheless, the electronic delocalisation through mesomerism is an essential feature of the invention and advantageously stabilizes the anion through additional bonds with the metal. Thus, R₂ and/or R₆ are preferably O, S, N-CN or N-SO₂CF₃, especially preferred O.

Either in combination with preferred R₂ and/or R₆ or independently thereof, R₃ and/or R₇ are much preferably H, halogen, NO₂, CN, COR₅₅, COOR₆₀, SO₃R₆₀, NCO or SCN, preferably H. Independently from the counter ion's structure, these preferred substituents surprisingly lead to an improved light and multiple read stability when used in optical recording media, either as the main recording dye or as an additive for other recording dyes, too.

It is especially preferred that, either in combination with preferred R₂, R₃, R₆ and/or R₇ or independently thereof, preferably in the heterocycle comprising Gi or G₂, at least one of R₄₂ and R₅₆ , especially R₄₂ , is CF₃, NO₂, CN, COR₅₅, COOR₆₀, CR₅₅OR₆I OR₆₂, CONR₆₃R₆₄, SO₂R₅₅, SO₃R₆₀, SO₂NR₆₃R₆₄, most preferred CF₃, NO₂, CN, COR₅₅, COOR₆₀, SO₂R₅₅ and/or SO₃R₆₀. Though both R₄₂ and R₅₆ may be such preferred groups, preferably only one of them is a preferred group and the other is hydrogen or Ci-C₄alkyl, or R₄₂ and R₅₆ are together butadienylen either unsubstituted or substituted, preferably unsubstituted or substituted by CF₃, NO₂, CN, COR₅₅, COOR₆₀ and/or SO₃R₆₀.

Preferably, either in combination with preferred R₂, R₃, R₆, R₇, R₄₂ and/or R₅₆ or independently thereof, especially in the heterocycle comprising G₃, R₅₈ is H or F, or together with R₄₄ is butadienylen either unsubstituted or substituted, preferably unsubstituted or substituted by one or more Ci-C₄alkyl, halogen, OR₆₀, SR₆₀, NR₅₅R₆I, CF₃, NO₂, CN, COR₅₅, COOR₆₀, SO₂R₅₅ and/or SO₃R₆₀.

Preferably, each R₆₀ is independently of any other R₆₀ alkyl or H, and each R₆₆ is independently of any other R₆e hydrogen or Ci-C₆alkyl, C₂-C₆alkenyl, C₂-C₆alkynyl, C₃-C₆cycloalkyl, C₃-C₆cycloalkenyl, C₂-C₅heterocycloalkyl or C₇-Ci iaralkyl each unsubstituted or mono- or poly-substituted by OR₇₂, SR₇₂, NR55R62 and/or COOR₅₅.

The number n is preferably 1 or 2.

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

Further preference, which is fully applicable in combination with any or all of above- mentioned preferences, is given to compounds of formula (I) wherein R₄ is hydrogen, hydroxy, Ci-C₄alkoxy or Ci-C₄alkyl; R₄₂ is nitro or cyano, preferably nitro; and/or R55 or R₄i 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, cyclopentylmethyl or cyclohexyl, each unsubstituted or mono- or poly-substituted by fluorine. R53 and R₅₄ are preferably both methyl, both ethyl or R₅₃ ethyl and R₅₄ methyl, or both together 1 ,5-pentylen. Alkyl, alkenyl, alkynyl, cycloalkyl and heterocycloalkyl are generally preferably Ci-C₄alkyl, C₂-C₄alkenyl, C₂-C₄alkynyl and epoxyalkyl, respectively. All these further preferences are fully applicable with particular benefits in the case of

preferred R₂, R₃, Re, R7, R42, R43, Rse, Reo and/or R₆e as well as

When R₅₅, R₆i and R₆₂ are bonded to one another in pairs by way of a direct bond or an -O-, -S- or -NR₈₂- bridge, they are preferably so bonded that a five- or six- membered ring is formed.

Another aspect of the invention are compounds of formula (I) wherein two cations or two ligands of the anion are bridged, for example by way of direct bonds or -O-,

-S- or -NR₈₂- bridges between any substituents in formula (I), it being possible for th e bridged ligands to be complexed either with the same metal cation or optionally with different metal cations, there being formed in the latter case oligomers which are, of course, also to be regarded as being subjects of the invention. Bridgings by way of O or N atoms of the cation or anion, either those in the chromophore or those on substituents, are especially advantageous.

Compounds comprising 2 or 3 different moieties of formula (I) linked together by bonds and/or bridges may be either symmetrical or preferably asymmetrical and can be made purposefully in close analogy to methods which are known perse. In the following illustrative examples (which are on no account limiting), X may be, for example, -CH₂-, -CH₂-CH₂-, -CH₂-O-CH₂- or -CH₂-NH-CH₂- :

The recording medium according to the invention, in addition to comprising the compounds of formula (I), 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(ll) acetate or cobalt(II) chloride, the ions of which may, for example, originate from the components used.

Interesting anions of formula (I) are especially those of the following formulae (all six bonds to the metal have similar length according to the X-ray data) :

Interesting compounds of formula (I), wherein one or more of R₁ to R₄ is different from the corresponding R₅ to R₈ and/or wherein d is different from G₂ may be prepared simply by mixed synthesis, two different ligands being metallated at the same time. The compounds of formula (I) having asymmetric ligands can either be isolated by customary methods, such as chromatography, or preferably used in admixture with the compounds of formula (I) having two identical ligands.

Interesting cations of formula (I) are especially those of the following formulae

Both the anions and cations can be prepared in close analogy to known methods, for example those disclosed in CH-390250, CH-560270, CH-577998, CH-608027, CH-1 098125, DE-1083000, DE-2262780, EP-O 029003, GB-1 111 014, US-3,014,041 , US-2004/0 187231 , WO95/01 772 and WO04/088649, or according or in analogy to the examples given below. This is also true for the salts of formula (I), some examples of which in no way restricting the invention are

and

Some compounds of formula (I) are new. Hence, the invention also relates to a compound of formula (I), wherein the cation Zi comprises a group of the formula

The invention also pertains to the use of a compound of formula (I) optical recording with a laser of wavelength below 600 nm, preferably from 350 to 500 nm, especially from 350 to 450 nm, and to a process for the optical recording or playback of information, wherein a laser beam of wavelength below 600 nm, preferably from 350 to 500 nm, especially from 350 to 450 nm, is focussed onto the recording track of a recording medium comprising a compound of formula (I).

The recording layer advantageously comprises a compound of formula (I) or a mixture of such compounds as main component, for example at least 30% by weight, preferably at least 60% by weight, especially at least 80% by weight. Further customary constituents are possible, for example other chromophores (for example those disclosed in WO 01/75873, or others having an absorption maximum at from 300 to 1000 nm), stabilisers, ¹θ2-, triplet- or luminescence- quenchers, melting-point reducers, decomposition accelerators or any other additives that have already been described in optical recording media. Preferably, stabilisers or fluoresence-quenchers are added if desired.

When the recording layer comprises further chromophores, the amount of such chromophores should preferably be small, so that the absorption thereof at the wavelength of the inversion point of the shortest-wavelength flank of the absorption of the entire solid layer is a fraction of the absorption of the pure compound of formula (I) in the entire solid layer at the same wavelength, advantageously at most ¹/3, preferably at most Vs, especially at most Vio. The absorption maximum is preferably higher than 425 nm, especially higher than 500 nm.

Stabilisers, ¹O₂-, triplet- or luminescence-quenchers are, for example, metal complexes of N- or S-containing enolates, phenolates, bisphenolates, thiolates or bisthiolates or of azo, azomethine or formazan dyes, such as bis(4-dimethylamino- dithiobenzil)nickel [CAS N⁰ 38465-55-3], ^®lrgalan Bordeaux EL, ^®Cibafast N or similar compounds, hindered phenols and derivatives thereof, such as ^®Cibafast AO, o-hydroxyphenyl-triazoles or -triazines or other UV absorbers, such as ^®Cibafast W or ^®Cibafast P or hindered amines (TEMPO or HALS, also as nitroxides or NOR-HALS), and also diimmonium salts, Paraquat™ or Orthoquat TM salts, such as ^®Kayasorb IRG 022, ^®Kayasorb IRG 040, optionally also as radical ion salts, such as N,N,N',N'-tetrakis(4-dibutylaminophenyl)-p-phenyleneamine- ammonium hexafluorophosphate, hexafluoroantimonate or perchlorate. The latter are available from Organica (Wolfen / DE); ^®Kayasorb brands are available from Nippon Kayaku Co. Ltd., and ^®lrgalan and ^®Cibafast brands are available from Ciba Specialty Chemicals Inc.

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, JP-A-07/262604 or JP-A-2000/272241. They may be, for example, salts of the metal complex anions disclosed above with any desired cations, for example the cations disclosed above, or metal complexes, illustrated, for example, by a

compound of formula

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).

The optical recording materials according to the invention exhibit excellent spectral properties of the solid amorphous recording layer. The aggregation tendency in the solid is surprisingly low for such compounds. Crystallites are unexpectedly and very advantageously not formed or are formed only to a negligible extent. The reflectivity of the layers in the range of the writing and reading wavelength is suitable for both low to high and high to low systems.

By virtue of those excellent layer properties it is possible to obtain a rapid optical recording having high sensitivity, high reproducibility and geometrically very precise mark boundaries - also for very short (2T) marks -, the complex refractive index and the reflectivity changing substantially, which gives a high degree of contrast. The differences in the mark lengths and the interval distances ("jitter") are very small, which enables a high storage density to be obtained using a relatively thin recording channel with a narrow track spacing ("pitch"). The dye layer quality is excellent, leading to high signal-to-noise ratio (CNR, PRSNR) and astonishingly low error rate (bER or SbER) upon play-back.

By virtue of the excellent solubility, including in apolar solvents, solutions can be used even in high concentrations without troublesome precipitation, for example during storage, so that problems during spin-coating are largely eliminated. This applies especially to compounds containing branched C₃-C₈alkyl.

Recording and playback can take place at the same wavelength, therefore advantageously requiring a simple optical system with a single laser source of advantageously from 350 to 500 nm, preferably from 370 to 450 nm. Especially preferred is the UV range from 370 to 390 nm, especially approximately 380 nm, or especially at the edge of the visible range of from 390 to 430 nm, more especially approximately 405 ± 5 nm. In the field of compact, blue or violet laser diodes (such as Nichia GaN 405 nm) with an optical system of high numerical aperture, the marks can be so small and the tracks so narrow that up to about 20 to 25 Gb per recording layer is achievable on a 120 mm disc. At 380 nm it is possible to use indium-doped UV-VCSELs (Vertical-Cavity Surface-Bnitting Laser), which laser source already exists as a prototype [Jung Han et al., see MRS Internet J. Nitride Semicond. Res. 5S1 , W6.2 (2000)].

The invention therefore relates also to a method of recording or playing back data, wherein the data on an optical recording medium according to the invention are recorded or played back at a wavelength of below 600 nm, preferably from 350 to 500 nm.

The recording medium is based on the structure of known recording media and is, for example, analogous to those mentioned above. It may be composed, for example, of a transparent substrate, a recording layer comprising at least one of the compounds of formula (I), a reflector layer and a covering layer, the writing and readout being effected through the substrate.

Suitable substrates are, for example, glass, minerals, ceramics and thermosetting and thermoplastic plastics. Preferred supports are glass and homo- or co-polymeric plastics. Suitable plastics are, for example, thermoplastic polycarbonates, polyamides, polyesters, polyacrylates and polymethacrylates, polyurethanes, polyolefins, polyvinyl chloride, polyvinylidene fluoride, polyimides, thermosetting polyesters and epoxy resins. Special preference is given to polycarbonate substrates which can be produced, for example, by injection-moulding. The substrate can be in pure form or may comprise customary additives, for example UV absorbers or dyes, as proposed e.g. in JP-A-04/167239 as light stabilisation for the recording layer. In the latter case it may be that in the range of the writing wavelength (emission wavelength of the laser) the dye added to the support substrate has no or at most only very low absorption, preferably up to a maximum of about 20% of the laser light focussed onto the recording layer.

The substrate is advantageously transparent over at least a portion of the range from 350 to 500 nm, so that it is permeable to, for example, at least 80% of the incident light of the writing or readout wavelength. The substrate is advantageously from 10 μm to 2 mm thick, preferably from 100 to 1200 μm thick, especially from 600 to 1100 μm thick, with a preferably spiral guide groove (track) on the coating side, a groove depth of from 10 to 200 nm, preferably from 20 to 90 nm, a groove width of from 100 to 400 nm, preferably from 150 to 250 nm, and a spacing between two turns of from 200 to 600 nm, preferably from 300 to 450 nm. Grooves of different cross-sectional shape are known, for example rectangular, trapezoidal or V-shaped. Analogously to the known CD-R and DVD-R media, the guide groove may additionally undergo a small periodic or quasi-periodic lateral deflection (wobble), so that synchronisation of the speed of rotation and the absolute positioning of the reading head (pick-up) are made possible. Instead of, or in addition to, the deflection, the same function can be performed by markings between adjacent grooves (pre-pits). With such geometry, it is advantageously possible to meet the HD DVD-R™ specifications.

The recording medium is applied, for example, by application of a solution by spin- coating, the objective being to produce a layer that is as amorphous as possible, the thickness of which layer is advantageously from 0 to 40 nm, preferably from 1 to 20 nm, especially from 2 to 10 nm, on the surface ("land") and, depending upon the geometry of the groove, advantageously from 20 to 150 nm, preferably from 30 to 100 nm, especially from 40 to 80 nm, in the groove.

Reflecting materials suitable for the reflector layer include especially metals, which provide good reflection of the laser radiation used for recording and playback, for example the metals of Main Groups 13- 15 and of the Sub-Groups 3 - 12 of the Periodic Table of the Elements. Al₁ In, Sn, Pb, Sb, Bi, Cu, Ag, Au, Zn, Cd, Hg, Sc, Y, La, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt and the lanthanide metals Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu and alloys thereof are especially suitable. On account of its high reflectivity and ease of production special preference is given to a reflective layer of aluminium, silver, gold or an alloy thereof (for example a white gold alloy), especially aluminium on economic and ecological grounds. The reflector layer is advantageously from 5 to 200 nm thick, preferably from 10 to 150 nm thick, especially from 50 to 120 nm thick, but reflector layers of greater thickness, for example 1 mm thick or even more, are also possible.

Materials suitable for the covering layer include chiefly plastics, which are applied in a thin layer to the reflector layer either directly or with the aid of adhesion promoters. It is advantageous to select mechanically and thermally stable plastics having good surface properties, which can be modified further, for example written on. The plastics may be thermosetting plastics and thermoplastic plastics. Directly applied covering layers are preferably radiation-cured (e.g. using UV radiation) coatings, which are particularly simple and economical to produce. A wide variety of radiation-curable materials are 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-C4alkyl groups in at least two ortho-positions of the amino groups, and oligomers with dialkylmaleinimidyl groups, e.g. dimethylmaleinimidyl groups. For covering layers that are applied using adhesion promoters it is preferable to use the same materials as those used for the substrate layer, especially polycarbonates. The adhesion promoters used are preferably likewise radiation-curable monomers and oligomers. Instead of the covering layer applied using an adhesion promoter there may also be used a second substrate comprising a recording and reflector layer, so that the recording medium is playable on both sides. Preference is given to a symmetrical structure, the two parts being joined together at the reflector side by an adhesion promoter directly or by way of an intermediate layer.

In such a structure, the optical properties of the covering layer, or the covering materials, are essentially unimportant per se provided that, where applicable, curing thereof e.g. by UV radiation is achieved. The function of the covering layer is to ensure the mechanical strength of the recording medium as a whole and, if necessary, the mechanical strength of thin reflector layers. If the recording medium is sufficiently robust, for example when a thick reflector layer is present, it is even possible to dispense with the covering layer altogether. The thickness of the covering layer depends upon the thickness of the recording medium as a whole, which should preferably be a maximum of about 2 mm thick. The covering layer is preferably from 10 μm to 1 mm thick.

The recording media according to the invention may also have additional layers, for example interference layers or barrier layers. It is also possible to construct recording media having a plurality of (for example from two to ten) recording layers. The structure and the use of such materials are known to the person skilled in the art. 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-A- 0 353 393 of TiO₂, Si₃N₄, ZnS or silicone resins.

It is also possible to construct recording media having a plurality of recording layers (for example 2, 3, 4, 5, 6, 7, 8, 9 or 10). In particular, a dual layer disk where both recording layers can be recorded and read from the same side can be used: for example Dual Layer HD DVD-R™ featuring 30 GB/side.

One way to manufacture such multilayer 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" or "reversed stack" consists of making on one hand a half-disk with the following embodiment: transparent substrate / recording layer / semi-reflective layer and on the other hand another half-disk with an inverted layer sequence: substrate / reflective layer / recording layer. 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 protec- tive layers can be introduced at various places when required, for example between the recording material and the adhesive layer. Such technique is described for example in WO 04/021 336 and in WO 04/042717. The groove geometries and layer thicknesses are essentially in the same range as described above, with the difference for the inverted stack half disk that recording is made on-groove. The thickness of the recording layer in the latter case is advantageously from 20 to 150 nm, preferably from 30 to 100 nm, especially from 40 to 80 nm on the groove, and, depending upon the geometry of the groove, advantageously from 30 to 200 nm, preferably from 40 to 150 nm, especially from 50 to 100 nm, in the groove.

Hence, the invention also pertains to an optical recording medium suitable for optical recording with a laser of wavelength below 600 nm, preferably from 350 to 500 nm, comprising a grooved substrate, a reflecting layer and at least two recording tracks, wherein the recording track comprises a compound of formula

or a mesomeric or tautomeric form thereof.

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 insensitive to those solvents. Suitable coating methods and solvents are described, for example, in EP-A-O 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, 1 -methoxy-2-propanol, isopropanol, n-propanol or n-butanol, hydroxyketones, for example diacetone alcohol or 3-hydroxy-3-methyl-2-butanone, hydroxy esters, for example lactic acid methyl ester or isobutyric acid methyl ester, or preferably fluorinated alcohols, for example 2,2,3,3-tetrafluoro-1 -propanol or 2,2,2-trifluoroethanol, and mixtures thereof. Further suitable solvents are well- known in the art and disclosed, for example, in EP-A-O 483 387.

The application of the metallic reflector layer is preferably effected by sputtering or by vapour-deposition in vacuo. 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 operation can advantageously be carried out continuously and achieves good reflectivity and a high degree of adhesiveness of the metallic reflector layer.

Recording is carried out in accordance with known methods by writing pits (marks) of fixed or variable length by means of a modulated, focussed laser beam guided at a constant or variable speed over the surface of the recording layer. Readout of information is carried out according to methods known perse by registering the change in reflection using laser radiation, for example as described in "CD-Player und R-DAT Recorder" (Claus Biaesch-Wiepke, Vogel Buchverlag, Wurzburg 1992). The person skilled in the art will be familiar with the requirements.

The information-containing medium according to the invention is especially an optical information material of the WORM type. It can be used, for example, analogously to CD-R (compact disc - recordable) or DVD-R (digital video djsc - recordable) in computers, and also as storage material for identification and security cards or for the production of diffractive optical elements, for example holograms.

Alternatively, however, there are also recording media which differ substantially from CD-R and DVD-R and in which recording and playback take place not through the substrate but through the covering layer (in-groove or on-groove recording). Accordingly, the respective roles of the covering layer and the substrate, especially the geometry and the optical properties, are reversed in comparison with the structure described above. Analogous concepts are described a number of times in Proceedings SPIE-lnt. Soc. Opt. Eng. 1999, 3864 for digital video recordings in conjunction with a blue GaN laser diode. For such recording media, which are especially suitable for a high storage density and have correspondingly small marks ("pits"), precise focussing is important, so that the manufacturing process, while essentially analogous, is considerably more awkward.

The compounds of formula (I) according to the invention, however, also meet the increased demands of an inverse layer structure surprisingly well. Preference is therefore given to an inverse layer structure having the layer sequence substrate, reflector layer, recording layer and covering layer. The recording layer is therefore located between the reflector layer and the covering layer. A thin covering layer approximately from 50 to 400 μm in thickness is especially advantageous (typically 100 μm for recording and reading with a numerical aperture of 0.85).

The recording and reflector layers in an inverse layer structure have in principle the same functions as indicated above. As with the groove geometry, they therefore usually have dimensions within the ranges indicated above.

The inverse layer structure requires particularly high standards, which the compounds used according to the invention fulfil astonishingly well, for example when the recording layer is applied to the metallic reflector layer and especially when a covering layer is applied to the recording layer, the covering layer being required to provide the recording layer with adequate protection against rubbing, photo-oxidation, fingerprints, moisture and other environmental effects and advantageously having a thickness in the range of from 0.01 to 0.5 mm, preferably in the range of from 0.05 to 0.2 mm, especially in the range of from 0.08 to 0.13 mm.

The covering layer preferably consists of a material that exhibits a transmission of 80% or above at the writing or readout wavelength of the laser. Suitable materials for the covering layer include, for example, those materials mentioned above, but especially polycarbonate (such as Pure Ace^® or Panlite^®, Teijin Ltd), cellulose triacetate (such as Fujitac^®, Fuji Photo Film) or polyethylene terephthalate (such as Lumirror^®, Toray Industry), special preference being given to polycarbonate. Especially in the case of directly applied covering layers, radiation-cured coatings, such as those already described above, are advantageous, for example SD 347™ (Dainippon Ink).

The covering layer can be applied directly to the solid recording layer by means of a suitable adhesion promoter. In another embodiment, there is applied to the solid recording layer an additional, thin separating layer of a metallic, crosslinked organometallic or preferably dielectric inorganic material, for example in a thickness of from 0.001 to 10 μm, preferably from 0.005 to 1 μm, especially from 0.01 to 0.1 μm, for example from 0.05 to 0.08 μm in the case of dielectric separating layers and from 0.001 to 0.02 μm in the case of metallic separating layers. Separating layers and corresponding methods are disclosed in WO 02/082438, to which reference is expressly made here. If desired, such coatings can be applied, for example, in the same thickness also between the support material and the metallic reflector layer or between the metallic reflector layer and the optical recording layer. This may be advantageous in certain cases, for example when a silver reflector is used in combination with sulfur-containing additives in the recording layer.

In a special variant, there is applied to the solid recording layer an additional, thin separating layer of a metallic, crosslinked organometallic or dielectric inorganic material, for example in a thickness of from 0.001 to 10 μm, preferably from 0.005 to 1 μm, especially from 0.01 to 0.1 μm. On account of their high reflectivity, metallic separating layers should advantageously be a maximum of 0.02 μm thick. Separating layers and corresponding methods are disclosed in WO 02/082438, to which reference is expressly made here.

In addition to comprising one or more compounds of formula (I) and optionally customary additives, the optical recording media according to the invention may also comprise other chromophores, preferably metal-free chromophores. Other chromophores may, if desired, be added in an amount of from 1 to 200% by weight, based on the total of the compounds of formula (I). The amount of other chromophores is preferably from 5 to 100% by weight, especially from 10 to 50% by weight, based on the total of the compounds of formula (I).

The optical recording disks comprising the compounds of formula (I) lead to excellent results when recorded and played back at 405 nm, particularly with respect to the reflectivity, modulation, jitter, PRSNR and/or bER or SbER. As disclosed above, it is possible to use them for high to low recording as well as for low to high recording.

Hence, the invention also pertains to an instant recording medium, wherein the maximum reflectivity of the recording track is from 14 to 28% after irradiation, on which track pits are writable with a 405 ± 5 nm laser of power 7 ± 5 mW, and the modulation of the pits measured with a 405 ± 5 nm laser of power 0.4 ± 0.2 mW is at least 0.30, preferably from 0.38 to 0.60 .

The modulation is defined as usual in the art as the ratio of the reflectivity ( R ) change before and after the pit mark formation: modulation = (R_max - Rmin) / Rmax-

The invention further pertains to an instant recording medium, wherein the reflectivity of the recording track is from 10 to 30%, preferably from 12 to 25% before irradiation, on which track pits are writable with a 405 ± 5 nm laser of power 5 ±4 mW, and the modulation of the pits measured with a 405 ± 5 nm laser of power 0.35 ± 0.15 mW is at least 0.30, preferably from 0.38 to 0.60.

Upon irradiation with a laser having a wavelength of 350-500 nm, the optical properties of the instant compounds change in a fully unexpected way. The imaginary part of the complex index of refraction (k) is readily lowered with high sensitivity, while the real part of the index of refraction (n) remains significant without changing much. Surprisingly, this unique combination leads to optical recording systems wherein the reflectivity decreases upon irradiation with a laser of power 5 ±4 mW having a wavelength of 350-500 nm. Extremely advantageously, it is possible to use a standard groove geometry, preferably the geometry matching the Blu-ray Disc™ standard such as described above. Likely owing to light interference phenomena, disks can be made which are either suitable for use with high to low recording polarity or show improved performance when used with low to high recording polarity.

Hence, the invention finally also relates to an optical recording medium comprising a recording dye which is bathochromic as compared with the laser wavelength, on which medium pits of lower reflectivity are written on a higher reflectivity track.

Such high to low optical recording medium has preferably a reflectivity of from 10 to 30%, preferably from 12 to 25% before irradiation, and a reflectivity of from 0 to 20%, preferably from 1 to 15% after irradiation with a laser of power 5 ±4 mW having a wavelength of 350-500 nm. Preferably, the compound of formula (I) used in such medium has an index of refraction (n) of 1.5 ± 0.4, especially 1.5 ± 0.25, most preferred 1.5 ± 0.15, with an extinction coefficient (k) of more than 0.20, typically from 0.25 to 0.60, especially from 0.25 to 0.50, most preferred from 0.30 to 0.40 at the laser writing and/or reading wavelength.

Highly surprisingly, the invention therefore provides an optical recording medium which is compatible with the Blu-ray Disc™ standard, enabling to use existing readers. This highly desirable goal had never been achieved in the prior art yet.

The examples which follow illustrate the invention, without limiting it ("%" are by weight where not otherwise specified):

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°C. In the course of 40 minutes, 100 ml of aqueous 4N 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°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 litres of water and dried for 24 hours at 60°C/ 10³ Pa, yielding 78 g of red-brown product of formula:

¹H-NMR [ppm]: 8.87 (s, H₃); 6.46 (s, H_b); 6.49/6.52 (d, H_c); 7.71 /7.74 (d, H_d).

Example 2: 25 g of the compound according to example 1 are introduced into 100 ml of dimethylacetamide and stirred at 23°C. Then 12.7 g of cobalt(II) acetate tetrahydrate are added. Both starting materials slowly dissolve and an almost black solution is formed which is stirred at room temperature for 3 hours. After that time a dark-red precipitate has formed, which is filtered with suction through a Buchner filter and washed with 20 ml of dimethylacetamide. The suction-filtered material is suspended, with stirring, in 1.2 litres of methanol. After the addition of 10 g of sodium acetate (anhydrous) the reaction mixture is heated to 60-65°C and clarified by filtration at that temperature. The filtrate is concentrated to 200 ml using a rotary evaporator and cooled to from 5 to 10°C, whereupon crystallisation begins. The precipitate is filtered with suction and washed with 50 ml of methanol of a temperature of 0-5°C. Drying at 50-55°C/ 10³ Pa yields 15 g of an almost black product of formula:

¹H-NMR [ppm]: 7.99 (s, H₃); 5.32 (s, H_b); 6.22/6.25 (d, H_c); 7.81 /7.85 (d, H_d).

Example 3 (synthesis of thiazolium): 4 g of 2,5-dimethylbenzothiazol and 3.48 g of iodomethane are dissolved with stirring in 15 ml of acetone. The solution is heated with stirring at 62°C for 5 hours, cooled down to room temperature and evaporated at 10³ Pa and 60°C yielding a quantitative yield of 1 ,2,5-trimethylbenzothiazolium iodide as an off-white powder of formula:

Example 4 (synthesis of styryl thiazolium): 1 g of the product according to example 3 and 0.58 g of 4-diethylamino-benzaldehyde are dissolved with stirring in 15 ml of chloroform. The solution is heated with stirring at 62°C for 5 hours, cooled down to 10°C and filtered. Washing twice each with 10 ml of cold methanol gave the product as a dark violet solid of formula:

Example 5 (synthesis of salt): 0.66 g of the product according to example 2 is added to 10 ml of methoxypropanol at 23°C. A solution of 0.50 g of the product according to example 4 in 10 ml of methanol is added and the resulting solution is stirred for 15 h at 23°C, thus giving a violet suspension. The product is filtered with suction through a Buchner filter and washed with methanol, then a 1 :1 mixture of methanol and water and finally with methanol. Drying at 40°C / 10³ Pa yields 0.67 g of an almost black product of formula:

¹H-NMR [ppm]: 8.77 (m, 1 H); 8.33 -7.80 (m, 7 H); 7.64 -7.48 (m, 4 H);

7.32 (m, 1 H); 6.81 (m, 1 H); 6.22 (d, 2 H); 5.30 (s, 2 H); 4.15 (s, 3 H); 3.37 (m, 4 H); 3.13 (s, 3 H); 1.15 (t, 6 H).

λ_max (ethanol solution): 523 nm (ε = 1 13900).

Example 6: 1.5 g of the compound according to example 5 are dissolved in 98.5 g of 2,2,3,3-tetrafluoropropanol and filtered through a 0.2 μm Teflon™ filter. The dye solution is then applied at 250 r.p.m. to a 1.2 mm thick, planar polycarbonate disc (diameter 120 mm) and the speed of rotation is increased to 1200 r.p.m. so that the excess of solution is spun off and a uniform solid layer is formed. After drying at 70°C for 20 minutes, 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, Germany). At 405 nm, the dye layer has a refractive index n of 1.52 and an extinction coefficient k of 0.24.

Examples 7- 106: The following compounds are made and measured in analogy with examples 1 -6:

Figure 1 shows the real part of the complex index of refraction (n) of a solid layer of the compound according to example 10. Figure 2 shows the imaginary part of the complex index of refraction (k) of a solid layer of the compound according to example 10. Figure 3 shows the absorption spectrum of a solid layer of the compound according to example 10.

The photostability is determined with a calibrated xenon lamp (Hanau). The relative decrease in absorption -D₂₄ at λ_maχ after 24 hours' irradiation under UV exposure is excellently low for all compounds of examples 7 to 106. Example 107: 0.95 g of the compound according to example 41 are dissolved in 99 g of 2,2,3,3-tetrafluoropropanol and filtered through a 0.2 μm Teflon™ filter. The dye solution is then applied at 400 r.p.m. to the surface of a 0.6 mm thick, grooved polycarbonate disc (groove depth 49 nm, groove width 215 nm, track pitch 400 nm) having a diameter of 120 mm. The excess of solution is spun off by increasing the speed of rotation up to 4000 r.p.m.. When the solvent is evaporated off, the dye remains behind in the form of a uniform, amorphous solid layer, characterized by an optical density of 0.60. Drying is carried out in a circulating-air oven at 70°C for 20 minutes. In a vacuum-coating apparatus, a 120 nm thick silver layer is then applied to the recording layer by sputter coating. An adhesive layer of a UV-curable photopolymer (XD 4760™, 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 405 nm and a numerical aperture of 0.65, marks are written into the active layer at speeds of 6.61 m ^■ s^~1. Read out is then performed on the same apparatus by applying a read power of 0.4 mW and the following dynamic parameters are determined: optimum recording power, reflectivity, 11 1 / 111 H modulation, 2T-11T signal asymmetry, CNR signal-to-noise ratio, multi- track PRSNR (Partial Response Signal to Noise Ratio).

Example 108 - 115: The same procedure is used as in example 107, with the difference that the compounds according to examples 10, 12, 13, 15, 37, 38 and 63 (which are particularly preferred as well as the compounds of examples 65, 66, 73, 74, 76, 83, 89, 90, 91 , 92, 94, 95, 96, 98, 99, 100, 101 , 102, 103 and 106) are used instead of the compound according to example 41. The test results of all examples 107 to 115 are summarized in the following table:

The recording characteristics are very good and overall satisfy the specifications of the HD DVD-R™ format. The smallest marks (2T) can be precisely written and detected, leading to particularly advantageous (near to zero) signal asymmetries.

Example 116: In a vacuum-coating apparatus (CDI ™, Balzers) a 50 nm thick silver reflector layer is applied onto a 1.1 mm thick grooved polycarbonate disc (diameter 120 mm, groove pitch 320 nm, groove depth 21 nm, groove width 150 nm). 2 g of the compound according to example 10 are dissolved in 100 g of 2,2,3, 3-tetra- fluoropropanol and filtered through a 0.2 μm Teflon filter. The dye solution is applied onto the reflector layer by the spin-coating method in order to form a uniform solid film having, after drying in an oven for 15 min at 70°C, an effective absorption of 0.59 at 560 nm wavelength obtained after substracting the absorption of the silver layer itself. A 40 nm thick dielectric layer (SiON) is successively applied by RF-sputtering in a vacuum-coating apparatus (SDS131 ™, Balzers). Finally a polycarbonate film covered on one side with a pressure-sensitive adhesive (Lintec, 100 μm total thickness) is bonded onto the dielectric layer. Using a commercial disc testing equipment (ODU-1000™ for Blu-ray^® Disc, Pulstec, Japan) based on a 407 nm laser diode and an objective lens numerical aperture of 0.85, marks are recorded on the disc with a linear speed of 5.28 m/s and a laser power of 7.1 mW. The unrecorded and recorded areas are then read back with 0.35 mW laser power and the following signal parameters are measured: reflectivity before recording = 14%; reflectivity measured on a recorded mark (8T length) = 2.9% showing a high to low signal polarity; modulation I8pp/I8H = 0.78 ; CNR = 52.8 dB ; crosstalk = 28.3 dB.

Example 1 17: It is proceded in close analogy to example 107, with the differences that the compound according to example 15 (n ₄o5πm = 1.24 / k₄₀5πm = 0.33) is used instead of the compound according to example 41 , and that the groove depth is 60 nm instead of 49 nm.

Example 1 18: 0.8 g of the compound according to example 15 are dissolved in 99.2 g of 2,2,3, 3-tetrafluoropropanol and filtered through a 0.2 μm Teflon™ filter. The dye solution is then applied at 400 r.p.m. to the surface of a 0.58 mm thick, grooved polycarbonate disc (groove depth 75 nm, groove width 187 nm, track pitch 400 nm) having a diameter of 120 mm. The excess of solution is spun off by increasing the speed of rotation up to 4000 r.p.m. . When the solvent is evaporated off, the dye remains behind in the form of a first uniform, amorphous solid layer, characterized by an optical density of 0.58 at 518 nm. Drying is carried out in a circulating-air oven at 70°C for 20 minutes. In a vacuum-coating apparatus (Twister™ , Balzers Unaxis) a 7 nm thick semi-transparent silver layer is then applied to the recording layer by sputter coating. A transparent UV-curable photo- polymer (573™, Eques) is then applied thereto by spin-coating, and a second grooved disc (made of Zeonor™ (Nippon Zeon), thickness 0.6 mm, diameter 120 mm, groove depth 81 nm, groove width 233 nm, track pitch 400 nm) is bonded thereto, with the grooved surface facing the photopolymer. The photopolymer is cured under UV light, forming a 25 μm thick solid transparent layer. The Zeonor™ substrate is then mechanically split away from the original disc and discarded. A second dye solution is prepared using the compound according to example 37, 1 g of which is dissolved in 99 g of 2, 2, 3, 3-tetrafluoropropanol. On the newly-formed polymer grooved surface, the second dye solution is applied by spin-coating, thus obtaining a second uniform, amorphous solid layer having an optical density of 0.45 at 551 nm after drying in a circulating-air oven as for the first layer. A 120 nm thick silver layer is then applied to the second recording layer by sputter coating in the same vacuum coating equipment as for the semi-transparent layer. An adhesive layer of a UV-curable photopolymer (XD4820™, Huntsman) is then applied thereto by spin-coating, and a second dummy polycarbonate disc (thickness 0.6 mm, diameter 120 mm) is adhesively bonded thereto.

On a commercial test apparatus (ODU-1000™, Pulstec Japan), using a laser diode of wavelength 405 nm and a numerical aperture of 0.65, marks are written into the first and second active layers at speeds of 6.61 m ^■ s^~1. Read out is then performed on the same apparatus by applying a read power of 0.6 mW and the following dynamic parameters are determined: Optimum recording power, Reflectivity after recording, 11 1 / 111 H modulation, 2T-1 1 T signal Asymmetry, CNR signal-to-noise ratio, multi-track PRSNR (Partial Response Signal to Noise Ratio). The test results are summarized in the following table:

The recording characteristics are good on both layers. With this set of two dyes, it is possible to make double layer discs reaching the levels of reflectivity and sensitivity as defined in the specifications of the Double Layer HD DVD-R™ format.

Example 1 19 (comparative): It is proceeded as in example 1 17, with the only difference that the compound of example 15 is replaced through the compound of the following formula (chemical formula 1 according to EP-1 587092 and EP-1 587093; n ₄₀5nm = 1.48 / k₄₀5nm = 0.29): (II).

The test results of examples 1 17 and 1 19 are summarized in the following table:

The recording medium based on the comparative compound of formula (II) has too low modulation, PRSNR and SbER, all not sufficient to meet the HD DVD-R™ specifications even through groove geometry optimization.

Example 120 (comparative): It is proceeded in close analogy to example 1 17, with the difference that the compound of formula (II) is replaced through the compound of following formula (n ₄o5πm = 1.30 / k₄₀5πm = 0.25):

The test results are summarized in the following table: _i E _peamx

The recording medium has much too low modulation and a very strong signal asymmetry, leading to non measurable CNR, PRSNR and SbER signals.

Comparative examples 1 19 and 120 shows clearly that the choice of cation is just as essential as the choice of anion. Good results are only obtained with the instant combination of cation and anion of formula (I).

Claims

Claims:

1. An optical recording medium suitable for optical recording with a laser of wavelength below 600 nm, preferably from 350 to 500 nm, comprising a grooved substrate, a reflecting layer and a recording track of width from 100 to 400 nm, preferably from 150 to 250 nm, depth from 10 to 200 nm, preferably from 20 to 90 nm, and pitch from 250 to 430 nm, preferably from 310 to 399.9 nm, wherein the recording track comprises a compound of formula

or a mesomeric or tautomeric form thereof, wherein

Zi is a cation having n positive charges, the iodide salt of which has an absorption band in the UV-A or visible range, the absorption maximum of which is at a wave- length of from 350 to 550 nm, which cation is selected from the group consisting of cations of the formulae

are each independently of the other

or or C₂-C₈heteroaryl unsubstituted or mono-

or poly-substituted by R47, R48, R49 and/or R₅o;

R₂ and/or R₆ are O, S or NR₆₅;

R₁3 and R35 are independently of each other Ci-C₂oalkyl, C₃-Ci₂cycloalkyl, Ci-Ci₂heterocycloalkyl, C₂-C₂oalkenyl, C₃-Ci₂cycloalkenyl, C₄-Ci₂heterocyclo- alkenyl, C₂-C₂₀alkynyl, C₇-Ci₈aralkyl, Ci-C₉heteroaryl, C₂-Ci₇heteroaralkyl, C₆-Ci₂aryl or Ci-Ci₂alkyl interrupted by from one to five non-successive oxygen and/or sulfur atoms and/or by from one to five identical or different groups NR₅₁ , each unsubstituted or mono- or poly-substituted by halogen, OR₆e, SR₆6, NR51R67, NR₅iCOR₆8, NR₅ICOOR₆₉, N R51 CON R₆₉R₇₀, NR₅iCN, OSiR₅₁R₆₈R₇I, COR₅i, CR₅IOR₆₈OR₇I, NO₂, CN, COOR₆₆, CONR₆₉R₇₀, SO₂R₅I, SO₂NR₆₉R₇₀, SO₃R₆₉;

R₂₂ and R₂₃ are each independently of the other Ci-Ci₂alkyl, C₂-Ci₂alkenyl, C₂-Ci₂alkynyl, C₇-Ci₂aralkyl, C₃-Ci₂cycloalkyl, C₃-Ci₂cycloalkenyl or C₂-Ci ihetero- cycloalkyl each unsubstituted or mono- or poly-substituted by halogen, OR₆₆, SR₆₆, NR₅iR₆₇, NR₅iCOR₆₈, NR₅iCOOR₆₆, N R₅₁ CON R₆₉R₇₀, NR₅iCN, COR₅I, CR₅iOR₆₈OR₇i, NO₂, CN, COOR₆₆, CONR₆₉R₇₀ and/or SO₂R₆₉ ;

NR_5I , C₂-Ci₂alkylen, C₂-Ci₂alkenylen, C₂-Ci₂cycloalkylen or C₂-Ci₂cycloalkenylen being each unsubstituted or mono- or poly-substituted by halogen, OR₆₆, SR₆₆, NR₅iR₆₇, NR₅iCOR₆₈, NR₅iCOOR₆₆, N R₅₁ CON R₆₉R₇₀, NR₅iCN, COR₅₁, CR₅₁OR₆SOR₇I, NO₂, CN, COOR₆₆, CONR₆₉R₇₀ and/or SO₂R₆₉ ; R24, R25, R27, R28, R29, R30, R31 and R₃2 are each independently of the other H, halogen, COR₅i, NO₂, CN, SO₃R₆9; or Ci-C₆alkyl, C₆-Ci₂aryl, C₇-Ci₂aralkyl each unsubstituted or mono- or poly-substituted by halogen, Ci-C₈alkyl and/or SO3R69;

, thus forming a

each R₇₂, independently of any other R_72, is independently of the others Ci-C₆alkyl, C₂-C₆alkenyl, C₂-C₆alkynyl, C₃-C₆cycloalkyl, C₃-C₆cycloalkenyl or C₂-C₅hetero- cycloalkyl each unsubstituted or mono- or poly-substituted by halogen, NR₅₅R₆₂, CN and/or COOR₅₅; or C₆-Ci₀aryl, C₇-Ci iaralkyl or Ci-C₅heteroaryl each unsubstituted or mono- or poly-substituted by Ci-C₄alkyl, halogen, NR₅₅R₆I, COR₅₅, CR₅₅OR₆I OR₆₂, NO₂, CN and/or COOR₆₂;

R₈₃, R₈₄, R₈₅ and R₈₆ are each independently of the other H, Ci-C₄alkyl, halogen, OR₆₆, SR₆₆, NR₅iR₆₇, COR₅I, NO₂, CN or COOCrC₄alkyl;

it being possible once or more times radicals of the same or different substituents each selected from the group consisting of R₁, R₃, R₄, R₅, R₇, R₈, R₉, R₁₀, R_{1 1}, R₁₂, R₁₃, R₁₄, R₁₅, R₁₆, R₁₇, R₁₈, R₁₉, R₂₀, R₂₁ , R₂₂, R₂₃, R₂₄, R₂₅, R₂₆, R₂₇, R₂₈, R₂₉, R₃₀, R₃₁, R₃₂, R₃₄, R₃₅, R₃₈, R₃₉, R₄₀, R₄₁ , R₄₂, R₄₃, R₄₄, R₄₅, R₄₆, R₄₇, R₄₈, R₄₉, R₅₀, R₅₁ ,

k is an integer from 1 , 2, 3 or 4; and n is an integer 1 , 2 or 3.

2. An optical recording medium according to claim 1 , wherein and/or

are independently from each other , preferably

_s _ S^.

^R ₄T<\ Tr °^r V^N" ■

^K ₄3

3. An optical recording medium according to claim 1 or 2, wherein R₂ and/or R₆ are O, S, N-CN or N-SO₂CF₃, preferably O.

4. An optical recording medium according to claim 1 , 2 or 3, wherein R₃ and/or R₇ are H, halogen, NO₂, CN, COR₅₅, COOR₆₀, SO₃R₆₀, NCO or SCN, preferably H.

5. An optical recording medium according to claim 1 , 2, 3 or 4, wherein in the heterocycle comprising Gi or G₂, at least one of R₄₂ and R₅₆ , especially R₄₂ , is CF₃, NO₂, CN, COR₅₅, COOR₆₀, CR₅₅OR₆iOR₆₂, CONR₆₃R₆₄, SO₂R₅₅, SO₃R₆₀, SO₂NR₆₃R₆₄, most preferred CF₃, NO₂, CN, COR₅₅, COOR₆₀, SO₂R₅₅ and/or SO₃R₆₀, or R₄₂ and R₅₆ are together butadienylen either unsubstituted or substituted, preferably unsubstituted or substituted by CF₃, NO₂, CN, COR₅₅, COOR₆₀ and/or SO₃R₆₀.

6. An optical recording medium according to claim 1 , 2, 3, 4 or 5, wherein in the heterocycle comprising G₃, R₅₈ is H or F, or together with R₄₄ is butadienylen either unsubstituted or substituted, preferably unsubstituted or substituted by one or more Ci-C₄alkyl, halogen, OR₆₀, SR₆₀, NR₅₅R_6I, CF₃, NO₂, CN, COR₅₅, COOR₆₀, SO₂R₅₅ and/or SO₃R₆₀.

7. An optical recording medium according to claim 1 , 2, 3, 4, 5 or 6, wherein Mi is Al³⁺, As³⁺, Au³⁺, Bi³⁺, Ce³⁺, Co³⁺, Cr³⁺, Dy³⁺, Er³⁺, Eu³⁺, Fe³⁺, Gd³⁺, Ho³⁺, Ir³⁺, La³⁺, Lu³⁺, Mn³⁺, Mo³⁺, Nb³⁺, Nd³⁺, Pm³⁺, Pr³⁺, Rh³⁺, Ru³⁺, Sb³⁺, Sc³⁺, Sm³⁺, Ta³⁺, Tb³⁺, Ti³⁺, [TiCI]³⁺, [TiOH]³⁺, Tm³⁺, V³⁺, [VO]³⁺, W³⁺, Y³⁺, Yb³⁺, [ZrCI]³⁺ or [ZrOH]³⁺, preferably Co³⁺ or Cr³⁺, and n is 1 or 2.

8. A compound of formula (I), wherein the cation Zi comprises a group of the formula

9. The use of a compound of formula (I) according to any claim 1 , 2, 3, 4, 5, 6, 7 or 8 in optical recording with a laser of wavelength below 600 nm, preferably from 350 to 500 nm.

10. A process for the optical recording or playback of information, wherein a laser beam of wavelength below 600 nm, preferably from 350 to 500 nm, is focussed onto the recording track of a recording medium according to any claim 1 , 2, 3, 4, 5, 6 or 7.

11. A process according to claim 10, wherein pits of modulation at least 0.30, preferably from 0.38 to 0.60 are written.

12. An optical recording medium according to claim 1 , 2, 3, 4, 5, 6 or 7, wherein the maximum reflectivity of the recording track is from 14 to 28% after irradiation, on which track pits are writable with a 405 ± 5 nm laser of power 7 ± 5 mW, and the modulation of the pits measured with a 405 ± 5 nm laser of power 0.4 ±0.2 mW is at least 0.30, preferably from 0.38 to 0.60.

13. An optical recording medium according to claim 1 , 2, 3, 4, 5, 6 or 7, wherein the reflectivity of the recording track is from 10 to 30%, preferably from 12 to 25% before irradiation, on which track pits are writable with a 405 ±5 nm laser of power 5 ±4 mW, and the modulation of the pits measured with a 405 ±5 nm laser of power 0.35 ±0.15 mW is at least 0.30, preferably from 0.38 to 0.60.

14. An optical recording medium according to claim 1 , 2, 3, 4, 5, 6 or 7, having a reflectivity of from 10 to 30%, preferably from 12 to 25% before irradiation, and a reflectivity of from 0 to 20%, preferably from 1 to 15% after irradiation with a laser of power 5 ±4 mW having a wavelength of 350-500 nm, the reflectivity after irradiation being lower than the reflectivity before irradiation.