Azo dye compound

An azo dye comprising a compound represented by formula (III):

• wherein V1 and V2 each represent a substituent;
• the substituents V1 and V2 each represent a substituent represented by W1 or W2 described below;
• when at least one V1 is a substituent represented by W1, V2 is a substituent represented by W2, or when at least one V1 is a substituent represented by W2, V2 is a substituent represented by W1;
• r represents 1 to 4;
• M1 represents a counter ion;
• m1 represents the number necessary for neutralizing charge;
• W1 represents a hydroxyl group, a primary, secondary or tertiary amino group, an acylamino group, or a sulfonamido group;
• W2 represents a nitro group, a cyano group, an alkoxycarbonyl group, an aryloxycarbonyl group, an alkyl- or aryl-sulfonyl group, a carbamoyl group, a sulfamoyl group, an alkenyl group, an alkynyl group, an aryl group, a heterocyclic group, a sulfo group, a carboxyl group, a heterocyclic oxy group, an ammonio group, an alkyl- or aryl-sulfinyl group, an alkyl- or aryl-sulfonyl group, an acyl group, or an aryl- or heterocyclic-azo group;
• and
• the compound represented by formula (III) optionally has a substituent other than those represented by V1 and V2.