Abstract: A composition for imaging a biological tissue or fluid comprising a compound of formula (A) and a biologically acceptable diluent or carrier, (A) wherein X represents one of a nitrogen atom, an oxygen atom, a sulphur atom, a phosphorus atom, or a selenium atom; R represents an aromatic group and/or an aliphatic group; p is an integer of 1 to 2; q and s are independently integers of 1, 2, 3, or 4; Y1, Y2, and Y3 independently represent a hydrogen atom, a deuterium atom, a fluorine atom, a chlorine atom, a bromine atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, a polyglycol group, an oxygen atom, a nitrogen atom, a cyano group, a nitro group; and/or wherein two or more of Y1, Y2, and Y3 may combine together to form a condensed ring.