Asymmetric cyanine dye

A compound represented by the following general formula (I) or a salt thereof:

• wherein R1, R2, R4, and R5 independently represent a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms or a substituted or unsubstituted aryl group, and R1 and R2 and/or R4 and R5 may bind to each other to form a ring;
• R3 represents a hydrogen atom or a sulfo group;
• R6, R7, R8, and R9 each independently represents a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted alkoxyl group having 1 to 6 carbon atoms, a substituted or unsubstituted amino group, nitro group or cyano group, and two of adjacent groups selected from the group consisting of R6, R7, R8, and R9 may bind to each other to form a ring;
• X1 and X2 each independently represents a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms or a substituted or unsubstituted aryl group;
• m1 represents 0 or 1;
• m2 represents 0 or 1;
• m3 represents 0 or 1;
• L1, L2, L3, L4, L5, L6, and L7 each independently represents a substituted or unsubstituted methine group, and when two or more of methine groups among the aforementioned methine groups have a substituent, the substituents may bind to each other to form a ring;
• M represents a hydrogen atom, a metal or a quaternary ammonium salt;
• and n represents an integer of 1 to 7 required to neutralize a charge.