Refining Lanthanide Luminescence in Metallacrowns by Systematic Alteration of Hydroximate Ligands
Lutter, Jacob
2018
Abstract
Metallacrowns (MCs) are highly tunable complexes which have seen a wide range of research application including single-molecule magnets, host-guest studies and Ln-luminescence. The first near-infrared (NIR) emitting MC was a lanthanide-zinc metallacrown (LnZn16) which can image human HeLa cells. Recently these MCs have expanded to include systems with gallium. This thesis focuses on the development of new structure types for GaMCs and the systematic modification of existing gallium based metallacrowns via alterations to the hydroximate ligands which act as antenna for lanthanide sensitization. A new LnGa6L9 complex is described that has a higher antenna to Ln ratio compared to previously reported GaMCs to explore the relationship between the number of hydroximate ligands and Ln sensitization. This is important since the luminescence intensity (brightness) of the Ln emission is the product of the molar absorption and the quantum yield (QY). The structure contains six Ga(III) with a single Ln(III) encapsulated within a framework that matches a [3.3.1] organic cryptate. This metallacryptate sensitized Pr3+, Nd3+, Sm3+, Tb3+, Ho3+, Er3+, and Yb3+ emission, and increased the molar absorbance to 4.5.104 M-1.cm-1. However, the QYs tended to be lower than previous GaMCs due to the proximity of high energy N-H oscillators, so the brightness of each series was similar. Slow magnetic relaxation was also studied and observed for Nd3+, Dy3+ and Yb3+; however, only Dy3+ exhibited a real relaxation barrier (Ueff = 12.7 K). These complexes could allow preparation of dual addressable “smart materials” which take advantage of both the luminescent and magnetic properties of Ln ions. New GaMCs prepared with 5-iodosalicylhydroximate and/or 5-iodoisophtalate ligands were investigated for three objectives. First, ring substitution on the hydroximate led to red shifted maximum absorbance from 310 nm to 325 nm π-π* bands. Second, iodide could enhance intersystem crossing (ISC) which might aid lanthanide sensitization. Enhanced sensitization efficiency is observed when iodide is on carboxylate ligands in the case of Er3+, but the cause is not yet known. Third, X-ray attenuation by these heavy atoms could yield bimodal MC based luminescent/computed tomography (CT) contrast agents. Both monomeric and dimeric gallium 12-MC-4 complexes were made, and diffusion ordered spectroscopy (PGSE-DOSY) showed that only the dimeric complexes were solution stable. So, three combinations were made which had 4, 8, or 12 iodides on the MC. A positive correlation between quantum yield of Ln emission and iodide content was observed in the case of Sm3+ and Er3+ (up to 3.35% and 1.82.10-2% respectively), suggesting a relationship between enhanced ISC and Ln emission. The brightness of these complexes were similar to a reported analog with no iodides. The ability to attenuate X-rays in DMF solutions was demonstrated, showing that these metallacrowns could be used as bimodal agents. Successful functionalization of metallacrowns using copper catalyzed alkyne azide cycloaddition (CuAAC) and Sonogashira coupling is also deomonstrated. An ethynyl functionality was added to GaMCs, and the ability to perform CuAAC on these MCs was shown by appending either benzyl azide or biotin functionalized azide. Selective coupling controllably forming either single or multiple functionalization was demonstrated. This synthetic control is important to defray costs for expensive azide coupling partners. This ethynyl functionality was also introduced to the original zinc containing metallacrown scaffold. Finally, two new biaryl hydroximates were synthesized with the goal of red shifting excitation energy and allowing for two photon absorbance in metallacrowns.Subjects
Metallacrowns Lanthanide Luminescence
Types
Thesis
Metadata
Show full item recordCollections
Remediation of Harmful Language
The University of Michigan Library aims to describe library materials in a way that respects the people and communities who create, use, and are represented in our collections. Report harmful or offensive language in catalog records, finding aids, or elsewhere in our collections anonymously through our metadata feedback form. More information at Remediation of Harmful Language.
Accessibility
If you are unable to use this file in its current format, please select the Contact Us link and we can modify it to make it more accessible to you.