NOVEL ANTENNAE FOR THE SENSITIZATION AND PROTECTION OF LANTHANIDE CATIONS EMITTING IN THE VISIBLE AND NEAR-INFRARED

Several lanthanide cations are luminescent in the visible and in the near-infrared (NIR) regions, with unique and advantageous luminescence properties compared to organic fluorophores, which make luminescent lanthanide complexes desirable for a range of applications including light amplification, optical telecommunications, biological imaging and bioanalytical techniques. To overcome the limitation of low absorptivity and weak luminescence of free lanthanide cations in solution, lanthanide complexes are formed with chromophoric groups that are capable of absorbing incident light, and transferring the resulting energy to the lanthanide cation thus sensitizing luminescence ("antenna effect"). Additionally, lanthanide cations must be protected from solvent molecules whose vibrational overtones efficiently deactivate lanthanide cation excited states through non-radiative routes. The research work presented here has focused on developing lanthanide species with improved photophysical properties, utilizing a variety of approaches to reach two main goals: providing efficient sensitization of lanthanide cations via the antennae effect and superior protection against non-radiative deactivation. In a relatively traditional coordination chemistry approach, natural product molecules of the flavonoid family were used as antennae for NIR emitting lanthanide cations. Using a nanomaterials approach to achieve improved protection from quenching, visible emitting lanthanide cations were incorporated into CdSe semiconductor crystals, which bring their own electronic properties, including broad absorbance bands with high epsilon values and size dependent band gaps. Thus, the nanocrystals are used to provide protection from quenching as well as sensitize lanthanide cations through the antennae effect. In an alternate nanomaterials approach NIR emitting Yb3+ and Nd3+ were incorporated into NaYF4 inorganic nanoparticle matrices that were coated with organic tropolonate sensitizing groups. The nanoparticle matrix protects the lanthanide cations from non-radiative deactivation while the surface bound chromophores provide antennae effect sensitization. In addition, upconverting NaYF4:Yb,Er nanocrystals were synthesized and their potential to serve as energy acceptors from a naphthalimide based antenna or energy donors to Quantum Dots were investigated. Finally, metal-organic frameworks (MOFs) were explored as method to sensitize NIR and visible emitting lanthanide cations by incorporating the lanthanide cations at metal sites in the MOF structure and/or as occupants of the pores of zinc based MOFs