LnIII Complexes Displaying ErIII-centered Upconversion Emission in Solution and the Solid State with YbIII, NdIII or a Porphyrin-based ligand as Activators

Texas Tech University, Lubbock TX

Investigators

Abstract

With the support of the Chemical Structure, Dynamics, and Mechanisms B (CSDM-B) program in the Division of Chemistry, Anne E. V. Gorden of Texas Tech University, Ana de Bettencourt-Dias of the University of Nevada, Reno, and Jorge Monteiro of California Polytechnic State University-Humboldt will study lanthanide complexes with erbium, ytterbium, and neodymium to develop new compounds that have the potential to display efficient upconversion emission both in the solid state and in solution. In two-photon upconversion, light of lower energy non-destructive wavelengths, such as infrared light, is converted to higher energy emission in the visible region of the electromagnetic spectrum through a materials-excitation mechanism. The development of these new metal complexes as water-soluble compounds is expected to enable their application as new luminescent probes for bio-imaging of cells in real time without the need to employ damaging, high-energy radiation. In the long term, such studies have the potential to open up new vistas for biomedical science, by providing enabling tools to study processes in cells and biological tissues without perturbing the biology. Such complexes might, for example, provide a new means of analyzing metabolic processes or the reactivity of metalloenzymes in living tissues, thereby introducing new readouts for both healthy cell biology and dysfunctional cell biology, as a possible diagnostic tool. While selected examples of Ln(III)-upconversion emission in the solid state exist, the parameters for efficient upconversion emission in solution are not well established. To probe these parameters, the Gordon research team will isolate multi-metallic Ln(III)-ion complexes with water-soluble naphthylsalophen-based ligands and pre-organized supramolecular structures and characterize their photophysical properties. Ln(III)-ions have characteristic line-like spectra with long-lived emission, which can be easily distinguished from background fluorescence. Importantly, toxicity and low cell penetrability are not inherent concerns with Ln(III)-complexes and the emission properties of these complexes are not dependent on their crystalline phase. To realize upconversion emission, a combination of Yb(III) and Er(III) or Nd(III) and Er(III) in the complexes is needed, requiring careful balance of the necessary stoichiometry. Using judiciously designed systems, Dr. Gordon and her team will tune the properties of the Ln(III)-ion complexes for improved solubility, biocompatibility, and photophysical properties. Optimally, such probes should be water-soluble, display high emission efficiencies at emission wavelengths that are easily discriminated from tissue and cell fluorescence, and should be excited at wavelengths that are not absorbed by or damaging to biological tissues. This work is expected to contribute to better understanding of the structure-luminescence relationship that leads to increased upconversion emission in the solid state and in solution. The insights gained from this work have the potential to help guide the design and development of effective new luminescent probes, ultimately for applications in biological imaging. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.