Azo compound or salt thereof, and dye-based polarizing film and dye-based polarizing plate containing same

An azo compound represented by the following formula (1) or a salt thereof:

• wherein
• A1 represents a naphthyl group which may have a substituent;
• A2, A3 and A4 are each independently represented by the following formula (2) or formula (3), and at least one of A2, A3 and A4 is represented by the formula (2):
• wherein
• R2 represents a hydrogen atom, a hydroxy group, a C1-4 aliphatic hydrocarbon group, a C1-4 alkoxy group, a substituted or unsubstituted amino group, or a C1-4 alkoxy group having a sulfo group;
• m2 represents an integer of 0 to 6;
• M represents a hydrogen atom or ion, a metal ion or an ammonium ion;
• and
• n3 represents an integer of 0 to 2, and
• wherein
• R3 and R4 each independently represent a hydrogen atom, a C1-4 aliphatic hydrocarbon group, a C1-4 alkoxy group, a C1-4 alkoxy group having a hydroxy group, or a C1-4 alkoxy group having a sulfo group;
• R1 represents a hydrogen atom, a hydroxy group, a C1-4 alkoxy group or a substituted or unsubstituted amino group;
• m represents an integer of 0 to 5;
• M represents a hydrogen atom or ion, a metal ion, or an ammonium ion;
• n represents 1 or 2;
• k represents 0 or 1;
• and
• each hydrogen atom on ring a and ring b may be substituted with the substituent R1 or substituent SO3M.