Patent ID: 7465814

Claim:
A sulfonate compound represented by a formula (I) below, where, in the formula (I), an atomic group A-O is an atomic group that forms a fluorescent compound upon cleavage of a covalent bond between the atomic group A-O and a sulfonyl group, one or a plurality of atomic groups B—SO 3 — are bonded to an atomic group A, B is benzene ring that is substituted by one or a plurality of electron-withdrawing groups, the electron-withdrawing group is at least one selected from the group consisting of an alkyl halide group (except a monochloroalkyl group, a monobromoalkyl group and a monoiodoalkyl group), a nitro group and a cyano group, and B may be the same or different in kind in the case where the plurality of B exist, the atomic group B is at least one selected from the group consisting of: a 2,4-dinitrophenyl group; a 2-nitro-(4-trifluoromethyl)phenyl group; a 2-nitro-4-methoxyphenyl group; a 4-nitro-2-methoxyphenyl group; a 2-nitro-4-methylphenyl group; a 4-nitro-2-methylphenyl group; a 2-nitro-4,6-dimethylphenyl group; a 4-nitro-2,6-dimethylphenyl group; a 2-nitro-4-chlorophenyl group; a 4-nitro-2-chlorophenyl group; and a 2-nitro-4-isopropylphenyl group, A is a formula represented by a formula (X-1) or (X-2) below, where, in the above formulae, each of X 1 , X 2 , Y 1 and Y 2 is hydrogen atom, a straight or branched alkyl group having 1 to 6 carbon atoms or a halogen, X 1 , X 2 , Y 1 and Y 2 may be the same or different, R 3 is a hydrogen atom, a nitro group, a methyl group, a chloro group or a methoxy group, and R 4 is a hydrogen atom, a nitro group, a trifluoromethyl group, a methyl group, an isopropyl group, a chloro group or a methoxy group, wherein a fluorescent compound formed upon cleavage of the covalent bond between the atomic group A-O and the sulfonyl group is at least one selected from the group consisting of: fluorescein and its derivatives.