18 research outputs found
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Beyond Traditional Superatom Ligands and Cores
This dissertation summarizes my research in the Roy group on the development, synthesis, and study of new N-heterocyclic carbene (NHC) based ligands and nickel phsophinidene core compositions of molecular clusters, also known as superatoms.
Chapter 1 introduces superatoms as atomically precise and discreet building blocks for use in the design and synthesis of novel materials. A brief history as well as selected synthetic strategies of superatoms will be introduced. The relevant materials properties of superatoms as well as their dependence on core composition and ligand structure will be discussed. Next, the use of superatoms with specialized or functionalizable ligands to synthesize new materials will be demonstrated. This chapter details the importance of the superatom ligands and core composition is the foundation that the subsequent chapters builds upon in developing these two areas.
Chapter 2 introduces a functionalized NHC as a potential superatom ligand. While not necessary for all superatom ligands, ligands that enable electronic access to the superatom core are attractive. In this chapter, the conductance of potential NHC based ligands are probed through the scanning tunneling microscope-based break-junction (STM-BJ) method. A novel method of forming single molecule junctions in situ was used and these ligands are found to display a length dependent conductance with strong coupling to the Au electrode, confirming their potential use as ligands for superatoms.
Chapter 3 describes the nature of the NHC–M bond in self-assembled monolayers (SAMs) on a Au(111) surface using high-resolution spectroscopy and theoretical calculations. This study was performed as a result of challenges and questions encountered during the work of Chapter 2. The results obtained from this study explore an important structure-function relationship of NHC ligands and have broader impact in materials chemistry beyond superatoms.
Chapter 4 explores the synthesis of superatoms with NHC ligands beyond simple imidazolium-based NHCs. This chapter describes the two primary synthetic techniques used and the synthesis of NHC-ligated superatoms. This work is also ongoing and characterization is limited to crude single crystal X-ray diffraction structures and select NMRs.
Finally, Chapter 5 details the use of uncommon organocyclophosphine reagents to synthesis novel nickel-phosphinidene molecular clusters, a potential new superatom. In this chapter the synthesis of a family of nickel-phosphinidene molecular clusters is described and studied. A potential application of these molecular clusters is explored through the thermolytic conversion to the industrially relevant Ni2P
Ultra-fast Au(III)-mediated Arylation of Cysteine
Through mechanistic work and rational design, we have developed the fastest organometallic abiotic Cys bioconjugation. As a result, the developed organometallic Au(III) bioconjugation reagents enable selective labeling of Cys moieties down to pM concentrations and allow for the rapid construction of complex heterostructures from peptides, proteins, and oligonucleo-tides. This work showcases how organometallic chemistry can be interfaced with biomolecules and lead to the range of reac-tivities that are largely unmatched by classical organic chemistry tools
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An Organometallic Gold(III) Reagent for 18F Labeling of Unprotected Peptides and Sugars in Aqueous Media
The 18F labeling of unprotected peptides and sugars with a Au(III)-[18F]fluoroaryl complex is reported. The chemoselective method generates 18F-labeled S-aryl bioconjugates in an aqueous environment in 15 min with high radiochemical yields and displays excellent functional group tolerance. This approach utilizes an air and moisture stable, robust organometallic Au(III) complex and highlights the versatility of designer organometallic reagents as efficient agents for rapid radiolabeling
Stepwise Ligand Exchange for the Preparation of a Family of Mesoporous MOFs
A stepwise
ligand exchange strategy is utilized to prepare a series
of isoreticular <b>bio-MOF-100</b> analogues. Specifically, <i>in situ</i> ligand exchange with progressively longer dicarboxylate
linkers is performed on single crystalline starting materials to synthesize
products with progressively larger mesoporous cavities. The new members
of this series of materials, <b>bio-MOFs 101</b>–<b>103</b>, each exhibit permanent mesoporosity and pore sizes ranging
from ∼2.1–2.9 nm and surface areas ranging from 2704
to 4410 m<sup>2</sup>/g. The pore volume for <b>bio-MOF 101</b> is 2.83 cc/g. <b>Bio-MOF-102</b> and <b>103</b> have
pore volumes of 4.36 and 4.13 cc/g, respectively. Collectively, these
data establish this unique family of MOFs as one of the most porous
reported to date
Stepwise Ligand Exchange for the Preparation of a Family of Mesoporous MOFs
A stepwise
ligand exchange strategy is utilized to prepare a series
of isoreticular <b>bio-MOF-100</b> analogues. Specifically, <i>in situ</i> ligand exchange with progressively longer dicarboxylate
linkers is performed on single crystalline starting materials to synthesize
products with progressively larger mesoporous cavities. The new members
of this series of materials, <b>bio-MOFs 101</b>–<b>103</b>, each exhibit permanent mesoporosity and pore sizes ranging
from ∼2.1–2.9 nm and surface areas ranging from 2704
to 4410 m<sup>2</sup>/g. The pore volume for <b>bio-MOF 101</b> is 2.83 cc/g. <b>Bio-MOF-102</b> and <b>103</b> have
pore volumes of 4.36 and 4.13 cc/g, respectively. Collectively, these
data establish this unique family of MOFs as one of the most porous
reported to date
Breaking Kinetic Record for Cysteine Bioconjugation with Organometallic Reagents
Through mechanistic work and rational design, we have developed the fastest abiotic Cys bioconjugation. As a result, the developed organometallic Au(III) bioconjugation reagents enable selective labelling of Cys moieties down to pM concentrations and allow for the rapid construction of complex heterostructures from peptides, proteins, and oligonucleotides. This work showcases how organometallic chemistry can be interfaced with biomolecules and lead to the range of reactivities that are unmatched by classical organic chemistry tools
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Using Bulky Dodecaborane-Based Dopants to Produce Mobile Charge Carriers in Amorphous Semiconducting Polymers.
Conjugated polymers are a versatile class of electronic materials featured in a variety of next-generation electronic devices. The utility of such polymers is contingent in large part on their electrical conductivity, which depends both on the density of charge carriers (polarons) and on the carrier mobility. Carrier mobility, in turn, is largely controlled by the separation between the polarons and dopant counterions, as counterions can produce Coulombic traps. In previous work, we showed that large dopants based on dodecaborane (DDB) clusters were able to reduce Coulombic binding and thus increase carrier mobility in regioregular (RR) poly(3-hexylthiophene-2,5-diyl) (P3HT). Here, we use a DDB-based dopant to study the effects of polaron-counterion separation in chemically doped regiorandom (RRa) P3HT, which is highly amorphous. X-ray scattering shows that the DDB dopants, despite their large size, can partially order the RRa P3HT during doping and produce a doped polymer crystal structure similar to that of DDB-doped RR P3HT; Alternating Field (AC) Hall measurements also confirm a similar hole mobility. We also show that use of the large DDB dopants successfully reduces Coulombic binding of polarons and counterions in amorphous polymer regions, resulting in a 77% doping efficiency in RRa P3HT films. The DDB dopants are able to produce RRa P3HT films with a 4.92 S/cm conductivity, a value that is ∼200× higher than that achieved with 3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), the traditional dopant molecule. These results show that tailoring dopants to produce mobile carriers in both the amorphous and semicrystalline regions of conjugated polymers is an effective strategy for increasing achievable polymer conductivities, particularly in low-cost polymers with random regiochemistry. The results also emphasize the importance of dopant size and shape for producing Coulombically unbound, mobile polarons capable of electrical conduction in less-ordered materials
Carrier density and delocalization signatures in doped carbon nanotubes from quantitative magnetic resonance
Abstract: High-performance semiconductor materials and devices are needed to supply the growing energy and computing demand. Organic semiconductors (OSCs) are attractive options for opto-electronic devices, due to their low cost, extensive tunability, easy fabrication, and flexibility. Semiconducting single-walled carbon nanotubes (s-SWCNTs) have been extensively studied due to their high carrier mobility, stability and opto-electronic tunability. Although molecular charge transfer doping affords widely tunable carrier density and conductivity in s-SWCNTs (and OSCs in general), a pervasive challenge for such systems is reliable measurement of charge carrier density and mobility. In this work we demonstrate a direct quantification of charge carrier density, and by extension carrier mobility, in chemically doped s-SWCNTs by a nuclear magnetic resonance approach. The experimental results are verified by a phase-space filling doping model, and we suggest this approach should be broadly applicable for OSCs. Our results show that hole mobility in doped s-SWCNT networks increases with increasing charge carrier density, a finding that is contrary to that expected for mobility limited by ionized impurity scattering. We discuss the implications of this important finding for additional tunability and applicability of s-SWCNT and OSC devices
Cyclopropenylidenes as Strong Carbene Anchoring Groups on Au Surfaces
The creation of stable molecular monolayers on metallic surfaces is a fundamental challenge of surface chemistry. N-Heterocyclic carbenes (NHCs) were recently shown to form self-assembled monolayers that are significantly more stable than the traditional thiols on Au system. Here we theoretically and experimentally demonstrate that the smallest cyclic carbene, cyclopropenylidene, binds even more strongly than NHCs to Au surfaces without altering the surface structure. We deposit bis(diisopropylamino)cyclopropenylidene (BAC) on Au(111) using the molecular adduct BAC-CO2 as a precursor and determine the structure, geometry, and behavior of the surface-bound molecules through high-resolution X-ray photoelectron spectroscopy, atomic force microscopy, and scanning tunneling microscopy. Our experiments are supported by density functional theory calculations of the molecular binding energy of BAC on Au(111) and its electronic structure. Our work is the first demonstration of surface modification with a stable carbene other than NHC; more broadly, it drives further exploration of various carbenes on metal surfaces
In Situ Formation of N‑Heterocyclic Carbene-Bound Single-Molecule Junctions
Self-assembled
monolayers (SAMs) formed using N-heterocyclic carbenes
(NHCs) have recently emerged as thermally and chemically ultrastable
alternatives to those formed from thiols. The rich chemistry and strong
σ-donating ability of NHCs offer unique prospects for applications
in nanoelectronics, sensing, and electrochemistry. Although stable
in SAMs, free carbenes are notoriously reactive, making their electronic
characterization challenging. Here we report the first investigation
of electron transport across single NHC-bound molecules using the
scanning tunneling microscope-based break junction (STM-BJ) technique.
We develop a series of air-stable metal NHC complexes that can be
electrochemically reduced in situ to form NHC–electrode contacts,
enabling reliable single-molecule conductance measurements of NHCs
under ambient conditions. Using this approach, we show that the conductance
of an NHC depends on the identity of the single metal atom to which
it is coordinated in the junction. Our observations are supported
by density functional theory (DFT) calculations, which also firmly
establish the contributions of the NHC linker to the junction transport
characteristics. Our work demonstrates a powerful method to probe
electron transfer across NHC–electrode interfaces; more generally,
it opens the door to the exploitation of surface-bound NHCs in constructing
novel, functionalized electrodes and/or nanoelectronic devices