Patent ID: 6939975

Claim:
A compound represented by the following formula (I) or a salt thereof: wherein R 1 and R 2 each independently represent a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms or a substituted or unsubstituted aryl group, and R 1 and R 2 may bind to each other to form a ring; R 3 , R 4 , R 5 and R 6 each independently represent hydrogen atom, a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted aryl group, a substituted or unsubstituted heteroaryl group, a halogen atom, cyano group, carboxyl group or sulfo group, and two of adjacent groups selected from the group consisting of R 3 , R 4 , R 5 and R 6 may bind to each other to form a ring; X 1 and X 2 each independently represent a substituted or unsubstituted alkyl group having 1 to 15 carbon atoms or a substituted or unsubstituted aryl group, and the total number of carboxyl groups existing in X 1 and X 2 is four or less, provided when the total number of carboxyl groups existing in X 1 and X 2 is 0 or 1, X 1 and X 2 each independently represent a carboxyalkyl group having 1 to 5 carbon atoms or a sulfoalkyl group having 1 to 5 carbon atoms, and at least one of R 3 , R 4 , R 5 and R 6 represents a substituted or unsubstituted aryl group or a substituted or unsubstituted heteroaryl group; L 1 , L 2 , L 3 , L 4 , L 5 , L 6 and L 7 each independently represent a substituted or unsubstituted methine group, and when two or more methine groups among the methine groups have a substituent, these substituents may bind to each other to form a ring, provided when X 1 and X 2 each have one carboxyl group, at least one methine group selected from the group consisting of L 1 , L 2 , L 3 , L 4 , L 5 , L 6 and L 7 represents a substituted methine group, and R 4 represents a sulfo group; M represents a hydrogen atom, a metal or a quaternary ammonium salt; Y represents nonmetallic elements required to form a 5- to 10-membered heterocyclic ring wherein said heterocyclic ring may be a condensed ring; and n represents an integer of 1 to 7 required to neutralize charge, wherein m 1 , m 2 and m 3 all represent 1.