1. An azo compound having a structure, of which a polymer having a monomer unit represented by formula (2) is bound to a structure
represented by formula (1):
wherein, in the formula (1), R1 and R2 each represent an OM group or an amino group, and M represents a hydrogen atom or a counter-cation; and R3 to R7 each represent a hydrogen atom or a linking group to be bound to the polymer, and at least one of R3 to R7 is the linking group;
wherein, in the formula (2), R8 represents a hydrogen atom or an alkyl group, and R9 represents a phenyl group, a carboxyl group, a carboxylic acid ester group or a carboxylic acid amide group.