Patent ID: 8143069

Claim:
A compound represented by the formula (I) or a salt thereof: wherein R 1 represents hydrogen atom or one to four monovalent substituents substituting on the benzene ring, and when R 1 represents two or more substituents, the substituents may be the same or different; R 2 , R 4 , R 5 , and R 7 independently represent hydrogen atom, or a monovalent substituent; R 3 is ═N + (R 8 )(R 9 ).M − , wherein R 8 and R 9 independently represent an alkyl group which may be substituted, and M − represents a counter ion; R 6 represents —N(R 10 )(R 11 ), wherein R 10 and R 11 independently represent an alkyl group which may be substituted; n represents an integer of 1 to 3; and X is —SH.