Lanthanide-centered Emission for Bioimaging, Sensing and Photodynamic Therapy
The optical properties of lanthanide ions make them uniquely suitable for lighting and imaging applications and their emission is most efficiently excited through a coordinated ligand. In the case of bioimaging, in addition to aqueous solubility, low energy sensitization is preferred, which can be achieved through either upconversion or two-photon absorption. In two-photon absorption, the ligand absorbs two consecutive low-energy photons, populating an excited state on the ligand; energy transfer occurs then to the lanthanide ion and emission is observed. Upconversion occurs directly through absorption of two low-energy photons by a lanthanide ion; this leads to population of a higher energy state on a second lanthanide ion, and emission from this higher energy level is observed. In this case, the ligands do not directly participate in the energy transfer, taking on the role of providing a low-phonon environment and anchoring the lanthanide ions in place and within suitable distances for energy transfer. Moreover, inclusion of certain functional groups in the lanthanide complexes enabled the generation of cytotoxic singlet oxygen. In my talk, I will discuss the synthesis and characterization of lanthanide ion complexes that display the characteristic metal-centered emission through direct sensitization and either two-photon absorption, using carbazolebased ligands, or upconversion, using triple-decker sandwich complexes with naphthylsalophen-based ligands, and initial results on the use of these complexes for confocal and two-photon imaging of the intracellular domain, as well as singlet oxygen generation for potential use in photodynamic therapy.