Read at: ACS Nano

Surface Chemistry Controls the Density of States in Metallic Nanoparticles

Nicholas P. Litak, Lillian M. Mawby, and Benjamin J. Lear

The density of electronic states near the Fermi energy of metallic systems is a critical parameter determining the physical and chemical behavior of metals.  We demonstrate that the Evans method of NMR can be used to measure this parameter and that the surface chemistry of gold nanoparticles can be used to adjust it. This is true even for changes in the length of alkanethiol ligands.


Asymmetries in the Electronic Properties of Spheroidal Metallic Nanoparticles, Revealed by Conduction Electron Spin Resonance and Surface Plasmon Resonance

Santina S Cruz, Vadim Tanygin and Benjamin J Lear

Size and shape are both known to control the electronic properties of nanoparticles. Using conduction spin electron spectroscopy, we demonstrate that for even very small metallic particles (<5nm diameter), asymmetries in shape result in asymmetry in the electronic properties. 


Preparation and Oxygen Sensitivity of a Range of Noble-Metal Nanoparticles (Ir, Pt, and Au) Protected by a Series of Chalcogen–Dodecane Ligands (S, Se, and Te)

Vadim Tanygin and Benjamin J Lear

Gold thiolate nanoparticles dominate the metallic nanoparticle literature, in part because of the Au-S interface is oxygen stable.  However, this property is not inherent to sulfur, but is an emergent property of the interface.  Using XPS, we demonstrate four additional interfaces with emergent oxygen stability: Ir-S, Pt-S, Ir-Se, and Pt-Se. 

Dependence of Core Electronics of Gold Nanoparticles on Ligand, Solvent, and Sample Preparation

Jonathan W Fagan and Benjamin J Lear

Nanoscale metallic particles are valued for their unique electronic properties.  Though particles of specific size, shape, and chemical interface are often targeted for these properties, the particles are often manipulated post synthesis, but prior to use.  Using conduction spin electron spectroscopy (CESR) as a measure of electronic properties, we show that manipulations like freezing and drying both result in perturbations of the electronic properties, and that the solvent choice plays a role in mediating these effects. 

Nanoscale heat for organic transformations: a photothermally driven retro Diels–Alder reaction

Andrea L Widstrom and Benjamin J Lear

Using the photothermal effect of gold nanoparticles, we drive a thermally activated endothermic retro-diels alder reaction. Though the heat supplied by these nanoparticles is localized to a scale of nanometers and the reactants are dilute, we find that the photothermal heating can drive the reaction at rates thousands of times greater than achieved using bulk-scale heating. 


Structural and solvent control over activation parameters for a pair of retro Diels-Alder reactions

Andrea L Widstrom and Benjamin J Lear

Using both solvent and substitution of the rings, we demonstrate control over the kinetic parameters of a series of retro-diels alder reactions. 

Controlled rapid formation of polyurethane at 700 K: Thermodynamic and kinetic consequences of extreme photothermal heating

Emma N Van Burns and Benjamin J Lear

Using photothermal heating by gold nanoparticles, we drive the curing of a polyurethane. Analyzing both the kinetic and equilibrium of the reaction under this heating, we are able to show the reaction proceeds at temperatures near 700K—a temperature well above the polymer’s thermal decomposition 

Photothermal control over the mechanical and physical properties of polydimethylsiloxane

R Joseph Fortenbaugh, Sabrina A Carrozzi and Benjamin J Lear

We show that using photothermal heating to drive the curing of PDMS provides a degree of control over the mechanicanical properties of the polymer. We note that photothermal heating produces the same efficiency of crosslinking, with an apparent decrease in the density of these crosslinks, ultimately leading to a decrease in the Young’s modulus of the polymer. 


Photothermal effectiveness of magnetite nanoparticles: Dependence upon particle size probed by experiment and simulation

Robert JG Johnson, Jonathan D Schultz and Benjamin J Lear

Using the photothermal effect of iron oxide nanoparticles to thermally degrade polypropylene carbonate, we demonstrate that the efficiency of degradation depends on the size of the nanoparticles—or more specifically to their heat capacity, which determines how much energy can be transferred to the polymer. 


On-demand curing of polydimethylsiloxane (PDMS) using the photothermal effect of gold nanoparticles

Robert JG Johnson and Benjamin J Lear

We demonstrate that the photothermal effect of gold nanoparticles can be used to enhance the real-time rate of curing of PDMS by a factor of at least 140, while the presence of the nanoparticles without illumination inhibits the curing. As part of this work, we also demonstrate how to synthesize gold nanoparticles directly in the polymer precursor.


Chain length and solvent control over the electronic properties of alkanethiolate-protected gold nanoparticles at the molecule-to-metal transion

Anthony Cirri, Alexey Silakov, Lasse Jensen, and Benjamin J. Lear

Using conduction electron spin resonance to probe the nature of the electronic states near the Fermi energy of metallic gold nanoparticles, we find that the g-factor for electrons in these states is sensitive to the length of the alkane chain.  In addition, changes in solvent result in changes in g-factor.  We propose a model that accounts for both of these behaviors, ascribing them to through-bond charge transfer and dielectric charging, respectively.  

Probing ligand-induced modulation of metallic states in small gold nanoparticles using conduction electron spin resonance

Anthony Cirri, Alexey Silakov, Lasse Jensen, and Benjamin J. Lear

We perform a Hammett parameter study for the g-factor of metallic electrons within gold nanoparticles decorated by para-substituted aromatic thiolates. We find that the g-factor is linearly dependent on the Hammett parameter.  Using computational results on a model cluster, we conclude that the most likely mode of action is changes in charge donation across the Au-S interface.  

Steady-state spectroscopic analysis of proton-dependent electron transfer on pyrazine-appended metal dithiolenes [Ni(pdt)2], [Pd(pdt)2], and [Pt(pdt)2] (pdt = 2,3-pyrazinedithiol)

Steven R. Kennedy, Morgan N. Kozar, Hemant P. Yennawar, and Benjamin J. Lear

By adjusting the energetic alignment between metal atoms and ligands, we find that we can tune how strongly the electron density in mixed valence species responds to asymmetric protonation of the ligands. 

Effect of protonation upon electronic coupling in the mixed valence and mixed protonated complex, [Ni(2,3-pyrazinedithiol)2]

Steven R. Kennedy, Puja Goyal, Morgan N. Kozar, Hemant P. Yennawar, Sharon Hammes-Schiffer, and Benjamin J. Lear

Pairing experiment with theory, we demonstrate that the asymmetric protonation of a nickel dithiolene complex results in severe reduction of the electronic coupling in the mixed valence state.  We postulate that the electron transfer and proton transfer coordinates are too tightly connected to allow for significant electronic coupling or facile electron transfer. 


Isolation and chemical transformations involving a reactive intermediate of MOF-5

Juyeong Kim, Michelle R Dolgos, and Benjamin J Lear

The ability to create new MOFs is critical to expanding their utility.  In molecular chemistry, the concept of a reactive intermediate is a powerful one.  Here, we demonstrate that such intermediates exist in the pathway to making MOF-5, and that this intermediate can be isolated and used as a synthetic branch point for the creation of a newly discovered MOF. 

Ligand control over the electronic properties within the metallic core of gold nanoparticles

Anthony Cirri, Alexey Silakov, Benjamin J Lear

Despite the fact that ligand control over the electronic properties of metal centers is the dominant paradigm in molecular inorganic chemistry, little is known about now the ligands on metallic nanoparticles influence their electronic structure.  Here, we demonstrate that electron spin resonance (ESR) on the conduction electrons provides a probe of the nature of the electronic states in the metallic core, and that these properties change with changes in ligands attached to the core. 

Structural, Electronic, and Magnetic Characterization of a Dinuclear Zinc Complex Containing TCNQ– and a μ-[TCNQ–TCNQ]2– Ligand

Juyeong Kim, Alexey Silakov, Hemant P Yennawar, Benjamin J Lear

TCNQ is a electron poor organic molecule that has long been prized for its reversible electrochemical behavior, as well as it is ability to form pi-pi stacks in conductive crystals.  Herein, we also show it can function as a ligand for Zn.  Indeed, as a ligand, it can go-exist as a monomer and a sigma-connected dimer. In the solid state, this complex is still characterized by pi-pi stacking between ligands. 

Electron-Transfer Reactions of Electronically Excited Zinc Tetraphenylporphyrin with Multinuclear Ruthenium Complexes

Jane Henderson, Starla D Glover, Benjamin J Lear, Don Walker, Jay R Winkler, Harry B Gray, Clifford P Kubiak

The driving force for electron transfer is a critical parameter for understanding, predicting, and controlling excited state electron transfer. Herein, we show that the coupling present in mixed valence molecules can be used to tube this electron transfer. 

Comparing the energetic and dynamic contributions of solvent to very low barrier isomerization using dynamic steady-state vibrational spectroscopy

Andrea N Giordano and Benjamin J Lear

The fast process of low-barrier isomerization can be difficult to follow and characterize.  Here, we show that we can use analysis of dynamically coalesced line-shapes in the infrared spectra of pianostool complexes to determine the rate of rotational isomerization—as well as the dependence of this isomerization on the parameters of the solvent in which it is dissolved. 

Billion-fold rate enhancement of urethane polymerization via the photothermal effect of plasmonic gold nanoparticles

Kaitlin M Haas and Benjamin J Lear

Driving thermally activated transformations is a nearly ubiquitous aspect of chemistry.  Using polyurethane we demonstrate that photothermal heating by nanoparticles can drive one important class of transformations: bond formation. We show that extreme heat results in extreme increases in reaction rates, and effective bond formation—even for this exothermic reaction. 

Fe 3 O 4 nanoparticles as robust photothermal agents for driving high barrier reactions under ambient conditions

Robert JG Johnson, Kaitlin M Haas and Benjamin J Lear

Though photothermal heating by nanoparticles can be effective at driving chemical transformations—such as the degradation of polypropylene carbonate—it is often the case that the nanoparticles are unstable during this process and change shape and size. These changes in shape in size have a detrimental effect on the control on can exert over photothermal heating. Here, we demonstrate that iron oxide nanoparticles can function as effective photothermal agents at extreme temperature, while displaying remarkable size, shape, structure, and ligand stability. 


Concentration-dependent dynamics of hydrogen bonding between acetonitrile and methanol as determined by 1D vibrational spectroscopy

Brian G Alberding and Benjamin J Lear

Using analysis of dynamically broadened vibrational lineshapes, we demonstrate that the dynamics of hydrogen bonding exchange between acetonitrile and methanol are dependent on the concentration of these constituents. In particular, we find that both the Arrhenius pre-exponential factor and the barrier to rotation change with concentration. 


Solvent versus Temperature Control over the Infrared Band Shape and Position in Fe(CO)3(η4-Ligand) Complexes

Andrea N Giordano and Benjamin J Lear

Using analysis of dynamically broadened vibrational line shapes, we we show that the rate of carbonyl rotation can be adjusted using both temperature and solvent effects.

Silica nanoparticles for enhanced carrier transport in polymer-based short channel transistors

Ali Veysel Tunc, Andrea N Giordano, Bernhard Ecker, Enrico Da Como, Benjamin J Lear, and Elizabeth Von Hauff

Silica nanoparticles are often added as filler to conducting polymer composites, where it is found that their presence can increase the conductivity of the films. Herein, we show that their inclusion leads to changes in the structure of the conducting polymer, which is the source of the increased conductivity.

Synthesis and characterization of ruthenium polypyridyl complexes with hydroxypyridine derivatives: effect of protonation and ethylation at the pyridyl nitrogen

Juyeong Kim, Hemant P Yennawar, and Benjamin J Lear

By appending a ligand with a free base onto a ruthenium center, we show that the MLCT band response to protonation. 

Degradation of polypropylene carbonate through plasmonic heating

Kaitlin M Haas and Benjamin J Lear


The photothermal effect of gold nanoparticles is shown to be effective at driving the thermal unzipping of polypropylene carbonate. 

Direct test of the equivalency of dynamic IR and dynamic raman spectroscopies as techniques for observing ultrafast molecular dynamics

Andrea N Giordano, Seth M Morton, Lasse Jensen, and Benjamin J Lear

Dynamic coalescence of infrared vibrational bands has been used previously to extract rates of ultrafast exchange.  However, the equivalent work in the Raman had not been done.  Here, we show that both Raman and IR give estimates of rates and thermal barriers that are, within error, the same. 


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