Symmetrical diazo compounds comprising 2-imidazolium groups and a non-cationic linke, compositions comprising them, method of coloring, and device

A dyeing composition comprising, in a medium appropriate for the dyeing of keratin fibers, as direct dye at least one compound of formula (I), or its acid addition salts,

• wherein:
• the radicals R1, which are identical or not, are chosen from:
• optionally substituted C1-C4 alkyl radicals;
• optionally substituted phenyl radicals;
• and
• optionally substituted benzyl radicals;
• the radicals R2, which may be identical or different, are chosen from:
• optionally substituted C1-C16 alkyl radicals optionally interrupted by at least one entity chosen from heteroatom and groups comprising at least one heteroatom, the alkyl radical being further optionally substituted by at least one group chosen from thio (—SH), C1-C4 thioalkyl;
• C1-C4 alkylsulphinyl or C1-C4 alkylsulphonyl groups;
• hydroxyl groups,
• C1-C4 alkoxy groups,
• C2-C4 (poly)hydroxyalkoxy groups;
• alkoxycarbonyl groups (RO—CO—) wherein R is chosen from C1-C4 alkyl radicals,
• alkylcarbonyloxy radicals (RCO—O—) wherein R is chosen from C1-C4 alkyl radicals,
• alkylcarbonyl radicals (R—CO—) wherein R is chosen from C1-C4 alkyl radicals,
• amino groups,
• amino groups substituted by one or two identical or different C1-C4 alkyl radicals optionally carrying at least one hydroxyl group, it being possible for the two alkyl radicals optionally to form, with the nitrogen atom to which they are attached, a heterocycle comprising from 1 to 3 heteroatoms chosen from N, O and S and 5 to 7 ring members, which is saturated or unsaturated, aromatic or non-aromatic and optionally substituted;
• alkylcarbonylamino groups (RCO—NR′—) wherein the radical R is chosen from C1-C4 alkyl radicals and the radical R′ is chosen from hydrogen and C1-C4 alkyl radicals;
• aminocarbonyl groups ((R)2N—CO—) wherein the radicals R independently of one another are chosen from hydrogen and C1-C4 alkyl radicals;
• ureido groups (N(R)2—CO—NR′—) wherein the radicals R and R′ independently of one another are chosen from hydrogen and C1-C4 alkyl radicals;
• aminosulphonyl groups ((R)2N—SO2—) wherein the radicals R independently of one another are chosen from hydrogen and C1-C4 alkyl radicals;
• alkylsulphonylamino groups (RSO2—NR′—) wherein R is chosen from C1-C4 alkyl radicals and R′ is chosen from hydrogen and C1-C4 alkyl radicals;
• optionally substituted aryl radicals;
• optionally substituted (C1-C4) alkylaryl radicals;
• alkylsulphinyl groups (R—SO—) wherein R is chosen from C1-C4 alkyl radicals;
• alkylsulphonyl groups (R—SO2—) wherein R is chosen from C1-C4 alkyl radicals;
• nitro groups;
• cyano groups;
• halogen atoms;
• thio groups (HS—);
• and
• alkylthio groups (RS—) wherein the radical R is chosen from optionally substituted C1-C4 alkyl radicals;
• when e is 2, the two radicals R2 may optionally form, with the carbon atoms to which they are attached, a secondary ring, aromatic or non-aromatic, comprising 5 or 6 ring members which is optionally substituted by at least one identical or non-identical group chosen from hydroxyl groups, C1-C4 alkyl groups, C1-C4 alkoxy groups, C2-C4 (poly)hydroxyalkoxy groups, amino groups, amino groups substituted by one or two identical or different C1-C4 alkyl radicals which optionally carry at least one hydroxyl group;
• e is an integer from 0 to 2;
• when e is less than 2, one or more unsubstituted carbon atom(s) of the heterocycle carry a hydrogen atom,
• the radicals R3, which may be identical or different, are chosen from:
• optionally substituted C1-C16 alkyl radicals optionally interrupted by at least one heteroatom or by at least one group comprising at least one heteroatom, hydroxyl groups,
• C1-C4 alkoxy groups,
• C2-C4 (poly)hydroxyalkoxy groups;
• alkoxycarbonyl groups (RO—CO—) wherein R is chosen from C1-C4 alkyl radicals,
• alkylcarbonyloxy radicals (RCO—O—) wherein R is chosen from C1-C4 alkyl radicals;
• alkylcarbonyl radicals (R—CO—) wherein R is chosen from C1-C4 alkyl radicals;
• amino groups;
• amino groups substituted by one or two identical or different C1-C4 alkyl radicals optionally carrying at least one hydroxyl group;
• it being possible for the two alkyl radicals optionally to form, with the nitrogen atom to which they are attached, a heterocycle comprising from 1 to 3 heteroatoms chosen from N, O and S and comprising 5 to 7 ring members, which is saturated or unsaturated, aromatic or non-aromatic and is optionally substituted;
• alkylcarbonylamino group (RCO—NR′—) wherein the radical R is chosen from C1-C4 alkyl radicals and the radical R′ is chosen from hydrogen and C1-C4 alkyl radicals;
• aminocarbonyl group ((R)2N—CO—) wherein the radicals R independently of one another are chosen from hydrogen and C1-C4 alkyl radicals;
• ureido groups (N(R)2—CO—NR′—) wherein the radicals R and R′ independently of one another are chosen from hydrogen and C1-C4 alkyl radicals;
• aminosulphonyl group ((R)2N—SO2—) wherein the radicals R independently of one another are chosen from hydrogen or a C1-C4 alkyl radicals;
• alkylsulphonylamino groups (RSO2—NR′—) wherein the radicals R and R′ independently of one another are chosen from hydrogen and C1-C4 alkyl radicals;
• thio groups (HS—);
• alkylthio groups (RS—) wherein the radical R are chosen from C1-C4 alkyl radicals;
• alkylsulphinyl groups (R—SO—) wherein R are chosen from C1-C4 alkyl radicals;
• alkylsulphonyl groups (R—SO2—) wherein R are chosen from C1-C4 alkyl radicals;
• nitro groups;
• cyano groups;
• and
• halogen atoms;
• when m′ is greater than or equal to 2, two adjacent radicals R3 may form, with the carbon atoms to which they are attached, a secondary ring, aromatic or non-aromatic, comprising 6 ring members, which is optionally substituted by at least one group chosen from the following groups:
• hydroxyl groups, C1-C4 alkyl groups, C1-C4 alkoxy groups, C2-C4 (poly)hydroxyalkoxy groups, C1-C4 alkylcarbonylamino groups, amino groups or, amino groups substituted by one or two identical or different C1-C4 alkyl radicals which optionally carry at least one hydroxyl group,
• m′ is an integer from 0 to 4;
• when m′ is less than 4, then one or more unsubstituted carbon atom of the aromatic ring carry a hydrogen atom;
• W1 radicals, which are identical, are chosen from:
• hydrogen,
• halogen atoms chosen from bromine, chlorine and fluorine,
• —NR4-Ph-NR5R6, —NR4-Ph-OR7, —O-Ph-OR7 and —O-Ph-NR5R6 group, where:
• R4 and R7, which may be identical or different, are chosen from hydrogen, optionally substituted C1-C20 alkyl radicals, optionally substituted aralkyl radicals and optionally substituted phenyl radicals;
• R5 and R6, which may be identical or different, are chosen from hydrogen, optionally substituted C1-C20 alkyl radicals, optionally substituted phenyl radicals, optionally substituted aralkyl radicals, and an alkylcarbonyl radical (R—CO—) wherein R is a C1-C4 alkyl radical;
• R5 and R6 may optionally form, with the nitrogen atom to which they are attached, a heterocycle comprising from 1 to 3 heteroatoms chosen from N, O and S and comprising 5 to 7 ring members, which is saturated or unsaturated, aromatic or non-aromatic and optionally substituted;
• Ph is chosen from optionally substituted phenyl radicals;
• —NR5—R6 groups, wherein R5 and R6, independently of each other, form, with the carbon atom of the aromatic ring adjacent to that to which —NR5R6 is attached, a 5- or 6-membered saturated heterocycle;
• the radicals R1, which may be identical or different, are chosen from:
• optionally substituted C1-C4 alkyl radicals;
• optionally substituted phenyl radicals;
• and
• optionally substituted benzyl radicals;
• L, a non-cationic linker connecting the two identical azo chromophores, is chosen from:
• covalent bonds;
• optionally substituted C1-C40 alkyl radicals optionally interrupted by a saturated or unsaturated, aromatic or non-aromatic (hetero)cycle comprising 3 to 7 ring members which are optionally substituted and optionally fused, the alkyls radical being optionally interrupted by at least one heteroatom or group comprising at least one heteroatom, with the proviso that the linker L not comprise an azo, nitro, nitroso or peroxo bonds;
• optionally substituted phenyl radicals;
• the electroneutrality of the compound of formula (I) being ensured by at least one identical or non-identical, cosmetically acceptable anions An.

A method of coloring keratin fibers comprising contacting the fibers, which are dry or wet, with a symmetrical cationic diazo compound chosen from those of formula (I) below, their resonance forms, and their acid addition salts and their solvates:

• wherein:
• the radicals R1, which are identical or not, are chosen from:
• optionally substituted C1-C4 alkyl radicals;
• optionally substituted phenyl radicals;
• and
• optionally substituted benzyl radicals;
• the radicals R2, which may be identical or different, are chosen from:
• optionally substituted C1-C16 alkyl radicals optionally interrupted by at least one entity chosen from heteroatom and groups comprising at least one heteroatom, the alkyl radical being further optionally substituted by at least one group chosen from thio (—SH), C1-C4 thioalkyl;
• C1-C4 alkylsulphinyl or C1-C4 alkylsulphonyl groups;
• hydroxyl groups,
• C1-C4 alkoxy groups,
• C2-C4 (poly)hydroxyalkoxy groups;
• alkoxycarbonyl groups (RO—CO—) wherein R is chosen from C1-C4 alkyl radicals,
• alkylcarbonyloxy radicals (RCO—O—) wherein R is chosen from C1-C4 alkyl radicals,
• alkylcarbonyl radicals (R—CO—) wherein R is chosen from C1-C4 alkyl radicals,
• amino groups,
• amino groups substituted by one or two identical or different C1-C4 alkyl radicals optionally carrying at least one hydroxyl group, it being possible for the two alkyl radicals optionally to form, with the nitrogen atom to which they are attached, a heterocycle comprising from 1 to 3 heteroatoms chosen from N, O and S and 5 to 7 ring members, which is saturated or unsaturated, aromatic or non-aromatic and optionally substituted;
• alkylcarbonylamino groups (RCO—NR′—) wherein the radical R is chosen from C1-C4 alkyl radicals and the radical R′ is chosen from hydrogen and C1-C4 alkyl radicals;
• aminocarbonyl groups ((R)2N—CO—) wherein the radicals R independently of one another are chosen from hydrogen and C1-C4 alkyl radicals;
• ureido groups (N(R)2—CO—NR′—) wherein the radicals R and R′ independently of one another are chosen from hydrogen and C1-C4 alkyl radicals;
• aminosulphonyl groups ((R)2N—SO2—) wherein the radicals R independently of one another are chosen from hydrogen and C1-C4 alkyl radicals;
• alkylsulphonylamino groups (RSO2—NR′—) wherein R is chosen from C1-C4 alkyl radicals and R′ is chosen from hydrogen and C1-C4 alkyl radicals;
• optionally substituted aryl radicals;
• optionally substituted (C1-C4)alkylaryl radicals;
• alkylsulphinyl groups (R—SO—) wherein R is chosen from C1-C4 alkyl radicals;
• alkylsulphonyl groups (R—SO2—) wherein R is chosen from C1-C4 alkyl radicals;
• nitro groups;
• cyano groups;
• halogen atoms;
• thio groups (HS—);
• and
• alkylthio groups (RS—) wherein the radical R is chosen from optionally substituted C1-C4 alkyl radicals;
• when e is 2, the two radicals R2 may optionally form, with the carbon atoms to which they are attached, a secondary ring, aromatic or non-aromatic, comprising 5 or 6 ring members which is optionally substituted by at least one identical or non-identical group chosen from hydroxyl groups, C1-C4 alkyl groups, C1-C4 alkoxy groups, C2-C4 (poly)hydroxyalkoxy groups, amino groups, amino groups substituted by one or two identical or different C1-C4 alkyl radicals which optionally carry at least one hydroxyl group;
• e is an integer from 0 to 2;
• when e is less than 2, one or more unsubstituted carbon atom(s) of the heterocycle carry a hydrogen atom,
• the radicals R3, which may be identical or different, are chosen from:
• optionally substituted C1-C16 alkyl radicals optionally interrupted by at least one heteroatom or by at least one group comprising at least one heteroatom, hydroxyl groups,
• C1-C4 alkoxy groups,
• C2-C4 (poly)hydroxyalkoxy groups;
• alkoxycarbonyl groups (RO—CO—) wherein R is chosen from C1-C4 alkyl radicals,
• alkylcarbonyloxy radicals (RCO—O—) wherein R is chosen from C1-C4 alkyl radicals;
• alkylcarbonyl radicals (R—CO—) wherein R is chosen from C1-C4 alkyl radicals;
• amino groups;
• amino groups substituted by one or two identical or different C1-C4 alkyl radicals optionally carrying at least one hydroxyl group;
• it being possible for the two alkyl radicals optionally to form, with the nitrogen atom to which they are attached, a heterocycle comprising from 1 to 3 heteroatoms chosen from N, O and S and comprising 5 to 7 ring members, which is saturated or unsaturated, aromatic or non-aromatic and is optionally substituted;
• alkylcarbonylamino group (RCO—NR′—) wherein the radical R is chosen from C1-C4 alkyl radicals and the radical R′ is chosen from hydrogen and C1-C4 alkyl radicals;
• aminocarbonyl group ((R)2N—CO—) wherein the radicals R independently of one another are chosen from hydrogen and C1-C4 alkyl radicals;
• ureido groups (N(R)2—CO—NR′—) wherein the radicals R and R′ independently of one another are chosen from hydrogen and C1-C4 alkyl radicals;
• aminosulphonyl group ((R)2N—SO2—) wherein the radicals R independently of one another are chosen from hydrogen or a C1-C4 alkyl radicals;
• alkylsulphonylamino groups (RSO2—NR′—) wherein the radicals R and R′ independently of one another are chosen from hydrogen and C1-C4 alkyl radicals;
• thio groups (HS—);
• alkylthio groups (RS—) wherein the radical R are chosen from C1-C4 alkyl radicals;
• alkylsulphinyl groups (R—SO—) wherein R are chosen from C1-C4 alkyl radicals;
• alkylsulphonyl groups (R—SO2—) wherein R are chosen from C1-C4 alkyl radicals;
• nitro groups;
• cyano groups;
• and
• halogen atoms;
• when m′ is greater than or equal to 2, two adjacent radicals R3 may form, with the carbon atoms to which they are attached, a secondary ring, aromatic or non-aromatic, comprising 6 ring members, which is optionally substituted by at least one group chosen from the following groups:
• hydroxyl groups, C1-C4 alkyl groups, C1-C4 alkoxy groups, C2-C4 (poly)hydroxyalkoxy groups, C1-C4 alkylcarbonylamino groups, amino groups or, amino groups substituted by one or two identical or different C1-C4 alkyl radicals which optionally carry at least one hydroxyl group,
• m′ is an integer from 0 to 4;
• when m′ is less than 4, then one or more unsubstituted carbon atom of the aromatic ring carry a hydrogen atom;
• W1 radicals, which are identical, are chosen from:
• hydrogen,
• halogen atoms chosen from bromine, chlorine and fluorine,
• —NR4-Ph-NR5R6, —NR4-Ph-OR7, —O-Ph-OR7 and —O-Ph-NR5R6 group, where:
• R4 and R7, which may be identical or different, are chosen from hydrogen, optionally substituted C1-C20 alkyl radicals, optionally substituted aralkyl radicals and optionally substituted phenyl radicals;
• R5 and R6, which may be identical or different, are chosen from hydrogen, optionally substituted C1-C20 alkyl radicals, optionally substituted phenyl radicals, optionally substituted aralkyl radicals, and an alkylcarbonyl radical (R—CO—) wherein R is a C1-C4 alkyl radical;
• R5 and R6 may optionally form, with the nitrogen atom to which they are attached, a heterocycle comprising from 1 to 3 heteroatoms chosen from N, O and S and comprising 5 to 7 ring members, which is saturated or unsaturated, aromatic or non-aromatic and optionally substituted;
• Ph is chosen from optionally substituted phenyl radicals;
• —NR5—R6 groups, wherein R5 and R6, independently of each other, form, with the carbon atom of the aromatic ring adjacent to that to which —NR5R6 is attached, a 5- or 6-membered saturated heterocycle;
• the radicals R1, which may be identical or different, are chosen from:
• optionally substituted C1-C4 alkyl radicals;
• optionally substituted phenyl radicals;
• and
• optionally substituted benzyl radicals;
• L, a non-cationic linker connecting the two identical azo chromophores, is chosen from:
• covalent bonds;
• optionally substituted C1-C40 alkyl radicals optionally interrupted by a saturated or unsaturated, aromatic or non-aromatic (hetero)cycle comprising 3 to 7 ring members which are optionally substituted and optionally fused, the alkyls radical being optionally interrupted by at least one heteroatom or group comprising at least one heteroatom, with the proviso that the linker L not comprise an azo, nitro, nitroso or peroxo bonds;
• optionally substituted phenyl radicals;
• the electroneutrality of the compound of formula (I) being ensured by at least one identical or non-identical, cosmetically acceptable anions An, for a time sufficient to give the desired effect.

A device comprising a plurality of compartments, wherein a first compartment comprises a symmetrical cationic diazo compound chosen from those of formula (I) below, their resonance forms, and their acid addition salts and their solvates:

• wherein:
• the radicals R1, which are identical or not, are chosen from:
• optionally substituted C1-C4 alkyl radicals;
• optionally substituted phenyl radicals;
• and
• optionally substituted benzyl radicals;
• the radicals R2, which may be identical or different, are chosen from:
• optionally substituted C1-C16 alkyl radicals optionally interrupted by at least one entity chosen from heteroatom and groups comprising at least one heteroatom, the alkyl radical being further optionally substituted by at least one group chosen from thio (—SH), C1-C4 thioalkyl;
• C1-C4 alkylsulphinyl or C1-C4 alkylsulphonyl groups;
• hydroxyl groups,
• C1-C4 alkoxy groups,
• C2-C4 (poly)hydroxyalkoxy groups;
• alkoxycarbonyl groups (RO—CO—) wherein R is chosen from C1-C4 alkyl radicals,
• alkylcarbonyloxy radicals (RCO—O—) wherein R is chosen from C1-C4 alkyl radicals,
• alkylcarbonyl radicals (R—CO—) wherein R is chosen from C1-C4 alkyl radicals,
• amino groups,
• amino groups substituted by one or two identical or different C1-C4 alkyl radicals optionally carrying at least one hydroxyl group, it being possible for the two alkyl radicals optionally to form, with the nitrogen atom to which they are attached, a heterocycle comprising from 1 to 3 heteroatoms chosen from N, O and S and 5 to 7 ring members, which is saturated or unsaturated, aromatic or non-aromatic and optionally substituted;
• alkylcarbonylamino groups (RCO—NR′—) wherein the radical R is chosen from C1-C4 alkyl radicals and the radical R′ is chosen from hydrogen and C1-C4 alkyl radicals;
• aminocarbonyl groups ((R)2N—CO—) wherein the radicals R independently of one another are chosen from hydrogen and C1-C4 alkyl radicals;
• ureido groups (N(R)2—CO—NR′—) wherein the radicals R and R′ independently of one another are chosen from hydrogen and C1-C4 alkyl radicals;
• aminosulphonyl groups ((R)2N—SO2—) wherein the radicals R independently of one another are chosen from hydrogen and C1-C4 alkyl radicals;
• alkylsulphonylamino groups (RSO2—NR′—) wherein R is chosen from C1-C4 alkyl radicals and R′ is chosen from hydrogen and C1-C4 alkyl radicals;
• optionally substituted aryl radicals;
• optionally substituted (C1-C4)alkylaryl radicals;
• alkylsulphinyl groups (R—SO—) wherein R is chosen from C1-C4 alkyl radicals;
• alkylsulphonyl groups (R—SO2—) wherein R is chosen from C1-C4 alkyl radicals;
• nitro groups;
• cyano groups;
• halogen atoms;
• thio groups (HS—);
• and
• alkylthio groups (RS—) wherein the radical R is chosen from optionally substituted C1-C4 alkyl radicals;
• when e is 2, the two radicals R2 may optionally form, with the carbon atoms to which they are attached, a secondary ring, aromatic or non-aromatic, comprising 5 or 6 ring members which is optionally substituted by at least one identical or non-identical group chosen from hydroxyl groups, C1-C4 alkyl groups, C1-C4 alkoxy groups, C2-C4 (poly)hydroxyalkoxy groups, amino groups, amino groups substituted by one or two identical or different C1-C4 alkyl radicals which optionally carry at least one hydroxyl group;
• e is an integer from 0 to 2;
• when e is less than 2, one or more unsubstituted carbon atom(s) of the heterocycle carry a hydrogen atom,
• the radicals R3, which may be identical or different, are chosen from:
• optionally substituted C1-C16 alkyl radicals optionally interrupted by at least one heteroatom or by at least one group comprising at least one heteroatom, hydroxyl groups,
• C1-C4 alkoxy groups,
• C2-C4 (poly)hydroxyalkoxy groups;
• alkoxycarbonyl groups (RO—CO—) wherein R is chosen from C1-C4 alkyl radicals,
• alkylcarbonyloxy radicals (RCO—O—) wherein R is chosen from C1-C4 alkyl radicals;
• alkylcarbonyl radicals (R—CO—) wherein R is chosen from C1-C4 alkyl radicals;
• amino groups;
• amino groups substituted by one or two identical or different C1-C4 alkyl radicals optionally carrying at least one hydroxyl group;
• it being possible for the two alkyl radicals optionally to form, with the nitrogen atom to which they are attached, a heterocycle comprising from 1 to 3 heteroatoms chosen from N, O and S and comprising 5 to 7 ring members, which is saturated or unsaturated, aromatic or non-aromatic and is optionally substituted;
• alkylcarbonylamino group (RCO—NR′—) wherein the radical R is chosen from C1-C4 alkyl radicals and the radical R′ is chosen from hydrogen and C1-C4 alkyl radicals;
• aminocarbonyl group ((R)2N—CO—) wherein the radicals R independently of one another are chosen from hydrogen and C1-C4 alkyl radicals;
• ureido groups (N(R)2—CO—NR′—) wherein the radicals R and R′ independently of one another are chosen from hydrogen and C1-C4 alkyl radicals;
• aminosulphonyl group ((R)2N—SO2—) wherein the radicals R independently of one another are chosen from hydrogen or a C1-C4 alkyl radicals;
• alkylsulphonylamino groups (RSO2—NR′—) wherein the radicals R and R′ independently of one another are chosen from hydrogen and C1-C4 alkyl radicals;
• thio groups (HS—);
• alkylthio groups (RS—) wherein the radical R are chosen from C1-C4 alkyl radicals;
• alkylsulphinyl groups (R—SO—) wherein R are chosen from C1-C4 alkyl radicals;
• alkylsulphonyl groups (R—SO2—) wherein R are chosen from C1-C4 alkyl radicals;
• nitro groups;
• cyano groups;
• and
• halogen atoms;
• when m′ is greater than or equal to 2, two adjacent radicals R3 may form, with the carbon atoms to which they are attached, a secondary ring, aromatic or non-aromatic, comprising 6 ring members, which is optionally substituted by at least one group chosen from the following groups:
• hydroxyl groups, C1-C4 alkyl groups, C1-C4 alkoxy groups, C2-C4 (poly)hydroxyalkoxy groups, C1-C4 alkylcarbonylamino groups, amino groups or, amino groups substituted by one or two identical or different C1-C4 alkyl radicals which optionally carry at least one hydroxyl group,
• m′ is an integer from 0 to 4;
• when m′ is less than 4, then one or more unsubstituted carbon atom of the aromatic ring carry a hydrogen atom;
• W1 radicals, which are identical, are chosen from:
• hydrogen,
• halogen atoms chosen from bromine, chlorine and fluorine,
• —NR4-Ph-NR5R6, —NR4-Ph-OR7, —O-Ph-OR7 and —O-Ph-NR5R6 group, where:
• R4 and R7, which may be identical or different, are chosen from hydrogen, optionally substituted C1-C20 alkyl radicals, optionally substituted aralkyl radicals and optionally substituted phenyl radicals;
• R5 and R6, which may be identical or different, are chosen from hydrogen, optionally substituted C1-C20 alkyl radicals, optionally substituted phenyl radicals, optionally substituted aralkyl radicals, and an alkylcarbonyl radical (R—CO—) wherein R is a C1-C4 alkyl radical;
• R5 and R6 may optionally form, with the nitrogen atom to which they are attached, a heterocycle comprising from 1 to 3 heteroatoms chosen from N, O and S and comprising 5 to 7 ring members, which is saturated or unsaturated, aromatic or non-aromatic and optionally substituted;
• Ph is chosen from optionally substituted phenyl radicals;
• —NR5—R6 groups, wherein R5 and R6, independently of each other, form, with the carbon atom of the aromatic ring adjacent to that to which —NR5R6 is attached, a 5- or 6-membered saturated heterocycle;
• the radicals R1, which may be identical or different, are chosen from:
• optionally substituted C1-C4 alkyl radicals;
• optionally substituted phenyl radicals;
• and
• optionally substituted benzyl radicals;
• L, a non-cationic linker connecting the two identical azo chromophores, is chosen from:
• covalent bonds;
• optionally substituted C1-C40 alkyl radicals optionally interrupted by a saturated or unsaturated, aromatic or non-aromatic (hetero)cycle comprising 3 to 7 ring members which are optionally substituted and optionally fused, the alkyls radical being optionally interrupted by at least one heteroatom or group comprising at least one heteroatom, with the proviso that the linker L not comprise an azo, nitro, nitroso or peroxo bonds;
• optionally substituted phenyl radicals;
• the electroneutrality of the compound of formula (I) being ensured by at least one identical or non-identical, cosmetically acceptable anions An, and a second compartment comprising an oxidizing composition.