A compound represented by the formula (I) (R.sup.1 represents hydrogen atom or a monovalent substituent; R.sup.2 and R.sup.3 represent hydrogen atom, an alkyl group, or a halogen atom; R.sup.4 and R.sup.5 represent an alkyl group or an aryl group; R.sup.6 and R.sup.7 represent hydrogen atom, an alkyl group, or a halogen atom; R.sup.8 represent hydroxy group or a dialkoxyboranetriyl group; and X represents silicon atom, germanium atom, or tin atom), which is a novel fluorophore usable as a mother nucleus of an off/on type fluorescent probe not utilizing the intramolecular photoinduced electron transfer.

To provide a novel class-A GPCR antagonist, a production method therefor, or a novel compound that interacts with a Na.sup.+-water cluster binding site of a class-A GPCR. Used is a compound or a salt thereof comprising a structure comprising a class-A GPCR-binding compound linked to a functional group that can bind to a Na.sup.+-water cluster binding site of the class-A GPCR. Also used is a method for producing a class-A GPCR antagonist, comprising the step of linking one compound with another compound that can bind to a Na.sup.+-water cluster binding site of the class-A GPCR.

To provide a novel class-A GPCR antagonist, a production method therefor, or a novel compound that interacts with a Na.sup.+-water cluster binding site of a class-A GPCR. Used is a compound or a salt thereof comprising a structure comprising a class-A GPCR-binding compound linked to a functional group that can bind to a Na.sup.+-water cluster binding site of the class-A GPCR. Also used is a method for producing a class-A GPCR antagonist, comprising the step of linking one compound with another compound that can bind to a Na.sup.+-water cluster binding site of the class-A GPCR.