A fluorescent monomer compound represented by the following formula (1) is provided: ##STR00001## wherein Q, Q' and D.sup.3 may be the same or different, may be combined together into a fused ring, and are each a substituent selected from the group consisting of a hydrogen atom, a halogen atom, a hydroxyl group, and substituted or unsubstituted alkyl, acyl, oxyalkyl, carboxyl, carboxylate ester, carboxamido, cyano, nitro, amino and aminoalkyl groups; and D.sup.1, D.sup.2 and D.sup.4 each represent a substituent, wherein at least one of D.sup.1, D.sup.2 and D.sup.4 is a substituent group comprising a vinyl group at an end thereof, and wherein the substituent group comprising a vinyl group at an end thereof enables the fluorescent monomer compound to be soluble in water.