Use for dyeing keratin fibres of a compound of azomethine type bearing a pyrazolopyridine unit

A compound chosen from dyes of azomethine type bearing a pyrazolopyridine unit of formula (I), leuco forms of formula (II) thereof, optical isomers and geometrical isomers thereof, tautomers thereof, addition salts thereof with an acid or a base, and solvates or hydrates thereof:

• wherein in formulae (I) and (II), independently:
• Z1 represents an oxygen atom or a group —NR6—;
• and when Z1 represents —NR6—, then R1 and R6 may form, together with the nitrogen atom to which they are attached, an optionally substituted, 5- to 8-membered, saturated, unsaturated or aromatic heterocycle;
• R1 and R6 each independently represent:
• a hydrogen atom;
• a C1-C10 alkyl radical optionally interrupted with one or more non-adjacent heteroatoms, and/or optionally substituted, with one or more groups chosen from i) hydroxyl, ii) optionally substituted 5- to 8-membered, saturated, unsaturated or aromatic (hetero)cycle, iii) —N(R′)R″, iv) —N+R′R″R′″ with R′, R″ and R′″ each independently representing a C1-C6 alkyl group;
• or
• an optionally substituted, saturated, unsaturated or aromatic 5- to 8-membered (hetero)cycle;
• R2, R3, R4 and R5 each independently represent:
• a hydrogen atom;
• an optionally substituted C1-C4 alkyl radical;
• or
• a group chosen from —NH2, —N(H)R10, —N(R11)—R12, —OH and —OR9, with R9 and R10 representing an optionally substituted, linear or branched C1-C6 alkyl, R11 and R12, which may be identical or different, representing an optionally substituted, linear or branched C1-C6 alkyl, it being optional for R11 and R12 to form, together with the nitrogen atom to which they are attached, a saturated, unsaturated or aromatic 5- to 8-membered heterocycle optionally containing one or more other heteroatoms or groups chosen from oxygen and nitrogen, the heterocycle being optionally substituted;
• R2, R3, R4 and R5 may form, in pairs, with adjacent radicals, an optionally substituted, saturated or unsaturated or aromatic (hetero)cycle;
• R′2 and R′3, which may be identical or different, represent:
• a hydrogen atom;
• a C1-C6 alkyl radical, optionally substituted with one or more hydroxyl radicals;
• a C1-C6 alkyl carboxylate radical;
• or
• a carboxyl radical;
• R′ represents:
• a hydrogen atom;
• a C1-C6 alkyl radical;
• R′6 represents:
• a hydrogen atom;
• a halogen atom;
• a linear or branched C1-C10 alkyl radical, optionally interrupted with one or more non-adjacent oxygen atoms and/or one or more non-adjacent divalent groups —N(R′9)— and optionally substituted with one or more radicals, which may be identical or different, chosen from —OH and —N(R′7)R′8;
• a carboxyl radical;
• a C1-C10 alkyl carboxylate;
• a radical CONR′7R′8;
• a C1-C10 alkoxy radical or a C1-C10 (poly)hydroxyalkoxy radical;
• a (poly)(C1-C10 alkoxy)-(C1-C10 alkoxy) radical;
• or
• a radical —O-Ak-N(R′9)R′10 in which Ak is a linear C1-C8 or branched C3-C8 divalent alkylene radical, optionally interrupted with one or more oxygen atoms and/or non-adjacent divalent groups —N(R′7)—;
• R′7 and R′8, which may be identical or different, represent:
• a hydrogen atom;
• or
• a C1-C8 alkyl radical optionally substituted with one or more hydroxyl radicals;
• R′9 and R′10, which may be identical or different, represent i) a linear or branched C1-C6 alkyl radical, ii) a C2-C6 alkenyl radical or iii) a C2-C6 alkynyl radical;
• R′9 and R′10 may form, with the nitrogen that bears them, a saturated or unsaturated 5- to 8-membered heterocycle, one of the chain members optionally being an oxygen atom or a nitrogen atom, or a divalent radical —N(R′11)— with R′11 representing a hydrogen atom or a C1-C4 alkyl group, optionally substituted with one or more radicals chosen from —OH, —N(R′7)R′8 and C1-C4 alkyl;
• R″ represents:
• a hydrogen atom;
• or
• a linear or branched C1-C10 alkyl radical, optionally interrupted with an oxygen atom or a divalent group —N(R)— with R representing a hydrogen atom or a C1-C4 alkyl group;
• wherein when the compound of formula (I) or (II) is positively charged, then it comprises as many anionic counterions as cationic charges to achieve the electrical neutrality of the molecule.