wherein R1, R2 and R2* each independently are selected from carbon-containing substituents forming a C—O bond with the neighbouring oxygen atom, R3 and R4 each represent a bond between the chromophoric moiety and other moieties of the chelate, and Ln3+ is a lanthanide ion, as well as the corresponding luminescence lanthanide chelating ligand. The application also discloses a detectable molecule comprising a biospecific binding reactant (such as an antibody) conjugated to the luminescent lanthanide chelate as well as a method of carrying out a biospecific binding assay, the use of such a detectable molecule in a specific bioaffinity based binding assay utilizing time-resolved fluorometric determination of a specific luminescence, and a solid support material conjugated with the luminescent lanthanide chelate.
