Trivalent lanthanide(III) ions, Ln3+, due to their specific electronic configuration ([Xe]4fn, n = 0–14) and the shielding of their 4f orbitals by the outer 5s25p6 subshells exhibit unique optical properties, in particular (i) sharp characteristic bands arising from f-f transitions in the entire spectrum from UV to near-infrared (NIR) domains, the wavelengths of which are insignificantly affected by changes in the local microenvironment around Ln3+ (pH, temperature, hydrophilic and hydrophobic character of biological molecules) and (ii) long luminescence lifetimes compared to organic fluorophores (ns-µs or µs-ms range for NIR- or visible-emitting Ln3+, respectively). However, extremely low molar absorption coefficients of free Ln3+ require their sensitization by the “antenna effect” via appropriate chromophoric ligands in order to obtain a sufficient emission intensity. Therefore, the design of highly luminescent Ln3+ compounds requires an optimization of the sensitization processes as well as the minimization of non-radiative deactivation mechanisms through overtones of high-energy vibrations, charge-transfer states and back energy transfer. Moreover, if Ln3+ coordination compounds are thought to be used in a specific application, additional requirements such as water solubility, biocompatibility, low toxicity, high thermodynamic stability and/or kinetic inertness for biological applications, have to be taken into account.
In this presentation, we will show the way from the design and synthesis to the use of highly luminescent lanthanide(III) coordination compounds emitting in the visible and the NIR ranges for biological applications. Particular attention will be given to the detailed analysis of photophysical properties in view of their possible rationalization. Ln3+-based small molecular complexes (polyaminocarboxylates, metallacrowns), macromolecules (dendrimers), coordination polymers and nanomaterials will be discussed.














Svetlana Eliseeva (Centre Moleculaire Biophysique in Orleans, France)