Structure-Property Relationships in Photoluminescent Lanthanide, Bismuth, and Lanthanide-Doped Bismuth Organic Hybrid Materials
Ayscue, Russell Lee
Knope, Karah E
Motivated by demands for novel luminescent materials and design strategies, this work focuses on the synthesis, structural characterization, and photoluminescent properties of solid-state lanthanide (Ln), bismuth (Bi), and Ln-doped bismuth organic hybrid materials. Collectively, this work provides fundamental insight into the structural features that enable and tune luminescent behavior in hybrid materials to inform future design strategies. For context, introductory descriptions of photoluminescent hybrid materials design, Bi coordination chemistry, and principal experimental methodologies are provided. Our research efforts towards Ln, Bi, and Ln-doped Bi photoluminescent hybrid materials are then presented. Homometallic Ln and heterometallic Ln-doped Bi hybrid compounds prepared with terpyridine (terpy) and 2-thiophenecarboylate(TC) ligands are described. Both the homometallic and doped materials exhibited ligand sensitized Ln3+ emission in the visible or near-infrared regions. While differences in Ln-doping percentages are attributed to structural breaks seen across the 4f series, comparison of luminescent properties of the Ln doped Bi materials to their closest homometallic Ln structural analogs, revealed enhanced quantum yield efficiencies within the doped materials. This enhanced luminescence is proposed to originate from the dilution of emissive Ln ions within the solid host lattice, increased asymmetry of the Ln dopant coordination environment, exclusion of quenching moieties, and/or potential Bi sensitization of Ln3+ emission. A second series of Ln-based compounds possessing phenanthroline (phen) and TC ligands were prepared and exhibited ligand and/or Ln3+ emissions depending on Ln identity. Heterometallic compounds produced dual emissions whose color is tuned by Ln compositions and excitation wavelength. This rare excitation dependent photoluminescent color tuning is anticipated to result from favorable energetic overlap of charge transfer absorptions facilitated by intermolecular π-π stacking interactions. Finally, a series of homometallic Bi halide organic compounds was found to produce broad yellow-green luminescence through visible excitation pathways. Combined experimental and computation efforts revealed that visible excitation likely originates from an intramolecular Bi-halide subunit to ligand orbitals charge transfer. The number of halides bound and structural distortions within the complex were identified as potential controls for the positioning of visible excitation bands. Furthermore, a series of europium-doped analogs retained visible excitation and exhibited photoluminescent color tuning based on europium-doping percentage.
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