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

Compound chosen from dyes of azomethine type comprising two pyrazolopyridine units of formulae (I) and (II), the leuco forms, optical and geometrical isomers, and tautomers thereof, and also the addition salts thereof with an acid or a base and the solvates thereof such as hydrates:

• in which formulae (I) and (II):
• Z1 represents an oxygen atom or a group —N(R6)—;
• Z′1 represents an oxygen atom or a group —N(R′6)—;
• when Z1 represents —N(R6)— and/or Z′1 represents —N(R′6)— then R1 and R6 and/or R′1 and R′6, respectively, may form, together with the nitrogen atom to which they are attached, an optionally substituted, 5- to 8-membered, optionally cationic, saturated, unsaturated or aromatic heterocycle;
• R1, R′1, R6, and R′6 each independently represent:
• a hydrogen atom,
• a C1-C10 alkyl radical optionally interrupted with one or more non-adjacent heteroatoms, preferably oxygen, and/or optionally substituted, preferably with one or more groups chosen from i) hydroxyl, ii) optionally substituted, 5- to 8-membered, cationic or non-cationic, 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;
• an optionally substituted, 5- to 8-membered, cationic or non-cationic, saturated, unsaturated or aromatic (hetero)cyclic radical;
• R2, R3, R4, R5, R′2, R′3, R′4 and R′5 each independently represent:
• a hydrogen atom,
• an optionally substituted C1-C4 alkyl radical,
• 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 possible 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 N, O, S, S(O)2 and C(O), the heterocycle being optionally substituted;
• R2, R3, R4, R5, R′2, R′3, R′4 and R′5 may form, in pairs with adjacent radicals, an optionally substituted, saturated or unsaturated (hetero)cycle;
• it being understood that 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.