This work deals with the engineering of a new luminescent complex of lanthanide, able to be specifically grafted onto biological materials and to emit a characteristic light useful in quantifying the concentration of the target molecules. We have based our molecular design on TbL1, wich possesses a significant quantum yield in water pointing to an efficient intramolecular energy transfer. We have elaborated the synthesis of a ligand derived from L1 and named L3, by functionalizing one of the chromophoric groups into a moiety able to couple the luminescent sensor to biological materials. The synthesis of the complexes was then realized. The thermodynamic study of the ligands L1 and L3, and their terbium complexes in water was made to establish the distribution diagrams and to compare their behaviour, especially at neutral pH. In addition, EuL1 was also investigated and the complexation constants of TbL1, EuL1 and TbL3 in water showed that these molecules are thermodynamically stable in aqueous media. Characterization of EuL3 in the solid state by high resolution luminescence allowed us to determine the geometry of the coordination sphere of the Eu(III) ion, which possesses a distorded C4 symmetry. The detailed study of the Eu(III) ion transitions evidenced two different sites, possibly arising from an equilibrium induced by the competition between a water molecule and the carboxylate function. This interpretation is in line with the measured lifetimes of the Tb(III) and Eu(III) excited states and the calculation of the hydration number of the complexes in aqueous solution. The determination of the energy of the singlet state and triplet states of the ligand, as well as of the emitting levels of the Ln(III) ions in solution showed that their relative values are favorable for a good intramolecular energy transfer. The quantum yields of TbL3 and EuL3, which amount to 2.6 % and 1.4 %, respectively, are lower than those of the complexes with L1, denoting that the presence of the acid function increases losses in the energy transfer. However, these values remain sizeable enough for potential biomedical applications. The study of the intermolecular energy transfer from EuL1, EuL3 and TbL3 to the acceptor Cy5 has proved promising, and the resulting yields were 90 % for EuL1 and 80 % for the complexes with L3.
EPFL2004
