Indole-derived styryl dye comprising an alkylene linker, a dye composition comprising this dye, and a process for lightening keratin materials using this dye

A fluorescent dye of formula (I):

• the organic or mineral acid salts thereof, optical isomers and geometric isomers thereof, or the solvates thereof:
• wherein:
• n is an integer ranging from 1 to 2;
• m is an integer ranging from 0 to 1;
• p is an integer ranging from 0 to 4;
• Q− is an anionic counterion;
• W is chosen from a (C2-C3)alkylene and a (C2-C3)alkenylene chain optionally substituted with at least one (C1-C4)alkyl or aryl group;
• Z1 is chosen from a carbon atom and a nitrogen atom N+ which is quaternized;
• Z2, Z3, and Z4, which may be identical or different, are chosen from a nitrogen atom, a CR4 group, and a N+R5 group;
• with the proviso that only one quaternized nitrogen atom N+ or N+R5 is present in the aromatic ring A;
• R1, R2, and R4, which may be identical or different, are chosen from a hydrogen atom, a halogen atom, a (di)(C1-C6)(alkyl)amino, a cyano, a hydroxyl, a (poly)halo(C1-C6)alkyl, an acyl(C1-C4)(alkyl)amino, a (C1-C6)alkoxy, a (C1-C6)alkylthio, a (poly)hydroxy(C2-C6)alkoxy, a (C1-C6)alkylcarbonyloxy, a (C1-C6)alkoxycarbonyl, a (C1-C6)alkylcarbonylamino, a (di)(C1-C4)(alkyl)aminocarbonyl, a (C1-C6)alkylsulfonyl(C1-C4)(alkyl)amino, a (di)(C1-C4)(alkyl)aminosulfonyl group, and a (C1-C6)alkyl group optionally substituted with a group chosen from (C1-C6)alkoxy, hydroxyl, and (di)(C1-C6)(alkyl)amino;
• or, when p is an integer greater than or equal to 2, two contiguous radicals R2 form, together with the carbon atoms to which they are attached, a benzo ring;
• R3 is chosen from a hydrogen atom, an optionally substituted (C1-C6)alkyl group, a (di)(C1-C6)(alkyl)amino group, an aryl group, and a heterocycloalkyl group which is optionally substituted;
• R5 is chosen from an optionally substituted (C1-C6)alkyl group and an aryl(C1-C6)alkyl;
• L is chosen from a σ bond and an optionally substituted C1-C20 divalent hydrocarbon-based chain, optionally interrupted i) with at least one divalent group or combination thereof chosen from:
• —N(R)—, —N+(R)(Ro)—, An−, —O—, —C(O)—, and —S(O)2—, wherein R and Ro, which may be identical or different, are chosen from a hydrogen, a (C1-C4)alkyl, a hydroxy(C1-C4)alkyl, and an amino(C1-C4)alkyl radical, and An− is an anionic counterion, or ii) with a cationic heterocycle or cationic heteroaryl Het+, An−, wherein An− is an anionic counterion and Het+ is chosen from a saturated or unsaturated heterocycle comprising from 5 to 10 members and a heteroaryl comprising from 5 to 10 members;
• with the proviso that, when n is 2, then m is 0, and when n is 1, then m is 1.