Use of polycationic compounds in the dyeing of keratinous fibres

Use, as direct dye in dyeing compositions for keratinous fibres, in particular human keratinous fibres, such as the hair, or for the manufacture of such compositions, of a compound of formula (I):

• in which:
• Xz′− denotes an organic or inorganic anion;
• z and z′ are such that the overall charge of the molecule is zero;
• A denotes a heterocyclic ring carrying a positive charge which has the following meaning:
• substituted or unsubstituted thiazolium, the substituents of the thiazolium comprising in total at most one alkoxycarbonyl functional group;
• substituted or unsubstituted imidazolium;
• substituted or unsubstituted benzimidazolium;
• substituted or unsubstituted benzothiazolium pyridino;
• substituted or unsubstituted naphthothiazolium and substituted benzothiazolium;
• B denotes an optionally substituted C6-C30 arylene group or an optionally substituted 5- to 10-membered heterocyclic group;
• L denotes a substituted or unsubstituted, linear, branched or cyclic, alkylene chain comprising from 1 to 30 carbon atoms, it being possible for the chain to be or not to be interrupted or terminated by one or more heteroatomic groups chosen from O, S, NH or NR, with R representing a linear or branched C1-C10 alkyl radical, or interrupted by one or more heterocyclic or nonheterocyclic, aromatic or nonaromatic, cyclice radicals, it being possible for the chain itself to carry one or more quaternary cationic charges and it being possible for one or more carbon atoms of the chain to be replaced by a carbonyl group;
• R1, R2 and R3 denote, independently of one another, an optionally substituted, linear, branched or cyclic C1-C10 arylalkyl radical;
• an optionally substituted aryl radical;
• or a linear or branched C1-C10 aryloxyalkyl radical;
• it being possible for at least one of the R1, R2, and R3 radicals to form, with the nitrogen atom carrying it (them) and optionally with L, an optionally substituted, saturated or unsaturated, 5- to 10-membered heterocycle which can comprise one or more additional heteroatoms.