Luminescent organic, transition metal, and lanthanide compounds for applications in light-emitting devices and biological imaging

Abstract

Luminescent materials are characterized by the emission of light upon a source of excitation whether it be from light, electricity, or physical stimuli. Over the past several centuries, research and understanding of luminescence has evolved, resulting in technologies which are now applied in a range of lighting devices, television screens, medical equipment, and microscopes. Lanthanides are favored for many of these applications due to their unique spectroscopic properties and low-energy excitation that is possible in the visible region, which arises from varying the type of sensitizing ligand. Different families of ligands, both organic and inorganic, can be used to sensitize lanthanide emission. Here, both organic ligands and transition metal complexes were used as lanthanide sensitizers to observe energy transfer from different ligands to lanthanides. Photoswitchable europium complexes were synthesized and studied for a responsive change in Eu(III) emission upon isomerization with light. An organic dipyridylphenazine-based bisthiophene ligand (5.1) was synthesized and displayed photochromic activity in both the free ligand and Eu(β-diketonate)₃(5.1) complexes. The complexes displayed photochromic activity, however, Eu(III) emission did not change upon isomerization, indicating that 5.1 played little to no role in Eu(III) emission. Another area of emissive complexes is focused on the synthesis of single-molecule white light emitters (SMWLEs). Common methods of producing white light rely on mixing components that each emit blue, green, and red light. Using a single molecule has many advantages over multicomponent systems, including no phase segregation, improved stability, good reproducibility, and stable Commission Internationale de l'Eclairage (CIE) coordinates. To achieve white light emission, a series of iridium(III)-europium(III) dyads containing a bridging pyridylthiazole-bis(pyrazolyl)pyridine (PTB) ligand and different cyclometalating ligands were synthesized and studied. White light was achieved in p-xylene solution with CIE coordinates of (0.23, 0.26). A second single molecule white light emitter was discovered in the solid-state emission of the bridging ligand mentioned above, PTB. Organic, solid-state SMWLEs are preferred due to their potential applications in next-generation solid-state lighting and potential for greater lighting efficiencies. PTB was found to emit at room temperature due to crystallization-induced emission from an energy transfer interaction in the solid state, with CIE coordinates of (0.38, 0.36).