A compound represented by formula (I):Formula (I) ##STR00001## wherein Z.sub.1 is atoms necessary for forming an aromatic ring; Z.sub.2 is atoms necessary for forming an aromatic hetero ring; V.sub.1 and V.sub.2 each are a substituent, and at least one of V.sub.1 and V.sub.2 is a hydroxyl, primary- or secondary- or tertiary-amino, acylamino, or sulfonamido group; r is 1 to 4; s is 1 to 4; the ring formed by Z.sub.1 or Z.sub.2 may have a substituent other than V.sub.1 or V.sub.2; M.sub.1 is a counter ion; m.sub.1 is the number necessary for neutralizing charge; and X.sub.1 and X.sub.2 each are a carbon or hetero atom, and at least one of X.sub.1 and X.sub.2 is a hetero atom.