Nanoparticles have been extensively studied in the past few decades due to the possibilities they offer in applications ranging from
medicine to energy generation. A new class of ultra-small noble metal nanoparticles consisting of tens to hundreds of atoms, commonly known
as clusters or nanoclusters, have drawn interest of the research community recently due to their unique optical, electronic and structural
properties. Over the past few years, advances have been made in the synthesis of atomically precise noble metal clusters (for example, silver
and gold) with distinct optical properties. Their ultra-small size distinguishes them from conventional plasmonic nanoparticles and the
properties are very sensitive to the slight variation in the compositon of the cluster, i.e. the number of the metal atoms and/or the nature
of the ligands. These clusters are interesting because of their potential applications in field such as sensing, imaging, catalysis, clean
energy, photonics, etc. as well as they provide fundamental insight into the evolution of the optical and electronic properties of these
clusters. In this project, we explored the strategies to synthesize luminescent metallic clusters of gold and silver and to promote their
solubility and stability in aqueous and biological medium. We focused particularly on the thiolate protected clusters due to the higher
affinity of gold and silver to sulfur. Lipoic acid (Thioctic acid) is a bio-molecule with a cyclic disulfide ring, which also acts as a
chelating ligand. Due to the higher binding affinity of the cyclic disulfide ring to nanocrystal surface, lipoic acid and chemically modified
lipoic acid molecules have been widely reported for the synthesis and functionalization of inorganic nanocrystals. Here, we describe the use
of bidentate lipoic acid ligands in the one phase growth of luminescent gold and silver nanoclusters. In addition, we have synthesized a new
set of monothiol ligands containing PEG and zwitterion for the functionalization of fluorescent clusters. Chapter 1 introduces the
fundamental properties of metallic clusters and the origin of these properties from electronic and structural point of view. The optical
properties of ultra-small nanocrystals (<2 nm) in comparison to the plasmonic particles is described. In addition, the variation of
optical and structural properties from one metal to another as well as one ligand to another is also compared. Chapter 2 describes the
synthesis of ultra-small size gold clusters with different optical emission (ranging from blue to red) using photo-activated LA-PEG ligands.
The influence of various factors on the growth of the clusters is also studied. Optical properties of the clusters were studied by UV-visible
absorption, PL emission and excitation and time resolved fluorescence spectroscopy. XPS and DOSY NMR were used to characterize the oxidation
states and sizes of these clusters. The photo-chemical transformation of LA-PEG ligands to thiols and the effect of various experimental
parameters such as solvent, oxygen, ligand functional group and effect of acid are described in chapter 3. Thiol yield percentage was
quantified using ellman assay. Chapter 4 describes the one phase aqueous synthesis of Ag29 clusters capped with bidentate dihydrolipoic acid
(DHLA). We also describe the drastic enhancement of the PL intensity upon gold doping of the Ag29 clusters. Optical properties along with the
size characterization by electrospray ionization mass spectrometry is also described. We further describe the growth of these clusters using
DHLA-PEG molecules. Chapter 5 describes the synthesis of highly fluorescent Au25-xAgx clusters stabilized with two types of ligands
(triphenylphosphine and thiols). We designed a set of monothiolate ligands appended with PEG and zwitterionic moieties. This approach allows
to prepare water soluble and stable metallic clusters with enhanced photoluminescence and well defined optical properties. Chapter 6 is the
overall summary of our findings and prospects and outlook. / A Dissertation submitted to the Department of Chemistry and Biochemistry in partial fulfillment of the
requirements for the degree of Doctor of Philosophy. / Fall Semester 2017. / November 15, 2017. / Includes bibliographical references. / Hedi Mattoussi, Professor Directing Dissertation; Peng Xiong, University Representative; Igor V.
Alabugin, Committee Member; Michael Shatruk, Committee Member; Geoffrey F. Strouse, Committee Member.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_604994 |
| Contributors | Mishra, Dinesh (author), Mattoussi, Hedi (professor directing dissertation), Xiong, Peng (university representative), Alabugin, Igor V. (committee member), Shatruk, Mykhailo (committee member), Strouse, Geoffrey F. (committee member), Florida State University (degree granting institution), College of Arts and Sciences (degree granting college), Department of Chemistry and Biochemistry (degree granting departmentdgg) |
| Publisher | Florida State University |
| Source Sets | Florida State University |
| Language | English, English |
| Detected Language | English |
| Type | Text, text, doctoral thesis |
| Format | 1 online resource (126 pages), computer, application/pdf |
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