Abstract: A fluorescing lanthanide chelate of a lanthanide cation and a compound having the structure ##STR1## where X.sup.3, X.sup.4 and X.sup.5 that may be the same or different, each denotes a substituted ethynyl group, hydrogen, an alkyl group, an aryl group, a hydroxyl group, an alkoxyl group or an amino group, wherein at least one of X.sup.3, X.sup.4 and X.sup.5 denotes a substituted ethynyl group, and Z.sup.2 and Z.sup.6 that may be the same or different, each denotes a chelating group, hydrogen, an alkyl group or an amino group, wherein at least one of Z.sup.2 and Z.sup.6 denotes a chelating group.