Development of Luminescent Terbium(III) Chelates for Protein Labelling: Effect of triplet-state energy level

The synthesis of novel TbIII labels suitable for protein labelling are reported. Their luminescence properties as antibody conjugates were measured and compared to the results of corresponding TbIII chelates of the parent ligand structures. When the lowest triplet-state energy level of the parent donor ligand was over 23000 cm−1, i.e., the energy gap between the 5D4 level of TbIII and the lowest triplet-state energy level of the ligand exceeded 2600 cm−1, the label derivative with a long decay time (τ = 1.35–2.93 ms) and a high luminescence yield (ϵ. Φ = 3770–4560) was found to be suitable for bioaffinity assays.