Novel bis-(pyrazol-1-yl)pyridine derivatives and lanthanide(III) complexes for emissive materials

Strohecker, Daniel James
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The electromagnetic emissions of the lanthanide series have served as inspiration for intense research in numerous fields, including emissive materials for lighting, displays, bioimaging, biomarkers, photodynamic cancer therapy, and laser material purposes. 2,6-bis(pyrazol-1-yl)pyridine (bppy) has been shown to effectively sensitize lanthanide emission, particularly when incorporated into a complex with europium tris(2-thenoyltrifluoroacetonate) (Eu(tta)₃). However, the majority of synthetic modification of this complex involves functionalization of the 4- position of the pyridine ring, or catalytic coupling of bppy species bearing halogen substituents at the 4- positions of the pyrazole rings. The unifying focus of this work is the development of novel syntheses to functionalize bppy at the 4- positions of the bppy pyrazole rings with functional groups other than halogen coupling products, such as nitro groups, amines, amides, imines, azides, azo- compounds, thiols, sulfides and sulfonate derivatives. The driving force of the synthesis of these novel functionalized ligands is the adaptation of the highly-luminescent Eu(tta)₃bppy complex for a variety of specific applications. Targeted synthesis of diarylamido-bppy derivatives was performed as an investigation into the development of a conjugation-interrupted metallopolymer for efficient emissive layers in OLED devices with the goal of preserving efficient Eu(III) ion sensitization while incorporating 3,4-ethylenedioxythiophene (EDOT) substituents which are readily electropolymerized. These new ligands and associated complexes were investigated by analytical techniques such as cyclic voltammetry, UV-vis absorption spectroscopy and spectrofluorimetry to quantitatively characterize the electronic energies which are vital to the light emission process from lanthanide ions. Analysis of these data gave insight into properties such as quantum yield, polymerization, and triplet-state energies to qualitatively assess emissive material performance. Additionally, synthetic routes to imino-, azo-, azido-, triazolyl-, mercapto-, sulfido- and sulfonic acid-bppy derivatives were pursued as means to broaden the scope of applications of this ligand system. Finally, the structural and spectroscopic properties of several novel lanthanide(III) species are reported and discussed. Ultimate conclusions, outlooks and further directions of each of these studies are also disclosed herein