Professional Appointments and Affiliations
Associate Professor of Chemistry
Associate Department Head for Facilities
126 Davey Lab
University Park, PA 16802
B.S. University of California, Davis, 2002
M.S. University of California, San Diego, 2004
Ph.D. University of California, San Diego, 2007
We are interested in the interaction between nanoparticles and their nearby chemical environment.
Chemical control over electronic properties of metal nanoparticles
In classical inorganic chemistry, ligands are used to control the electronic properties of the metal centers to which they are attached, in turn effecting a myriad of important properties, such catalytic activity. As a result, ligand control has emerged as the dominant paradigm in inorganic complex design and the large body of work in this area has produced a predictive framework that allows for efficient design of new inorganic complexes.
We are interested in understanding the extent to which the insights gained in traditional inorganic chemistry can be extended to control the properties of nanoscale materials. Specifically, we wish to understand the extent to which changes in the ligands bound to metallic nanoparticles can be used to effect changes in the electronic structure of these nanoparticles. For this, we synthesize new surfactants/nanoparticle composites and then study their electronic behavior using UV-visible and EPR spectroscopies. Together, this approach yields detailed insight into the dependence of the electronic properties of nanoparticles upon their ligand chemistry.
Photothermally driven chemical transformations
Heat is one of the oldest and most useful tools for promoting chemical transformations. It is prized for its generality, as any thermally activated transformation can be effectively driven simply by setting an appropriate temperature – without need to consider the specifics of the chemical reaction. This generality, of course, also leads to known-known problems, such as the promotion of unwanted chemical reactions.
We believe that much of the disadvantage of heat stems from the scale at which it is applied: typically longer than centimeters and for many minutes. If one compares these scales with those of the elementary steps of reactions (shorter than nanometers and picoseconds), it is easy to see that there is a large mismatch in time and space between the scale off the desired transformation and the application of heat. This lack of matching in terms of scale leads to imprecise usage of heat.
In my lab, we attempt to overcome this poor scale matching by using the photothermal effect of nanoparticles to produce elevated temperatures on scales close to those for elementary steps of reaction. For instance, a 30 nm gold nanoparticle that absorbs a nanosecond pulse of light is capable of producing temperatures on the order of 2000 K, but only over a few nanometers and for a few nanoseconds. We have been able to demonstrate that these localized and transient temperatures are able to drive conventional organic chemical reactions (such as polymerization of urethane) cleanly – even at such extreme temperatures. Further work in our lab focuses on understanding the breadth of this approach as well as how to best tune the effect for promoting desired chemical transformations.
Robert J. G. Johnson, Jonathan D. Schultz, and Benjamin J. Lear, “Photothermal Effectiveness of Magnetite Nanoparticles: Dependence upon Particle Size Probed by Experiment and Simulation,”Molecules,23,1234 (2018)
R. Joseph Fortenbaugh and Benjamin J. Lear, “On-demand curing of polydimethylsiloxane (PDMS) using the photothermal effect of gold nanoparticles,” Nanoscale, 9, 8555–8559 (2017)
Anthony Cirri, Alexey Silakov, Lasse Jensen, and Benjamin J. Lear, “Chain Length and Solvent Control over the Electronic Properties of Alkanethiolate Protected Gold Nanoparticles at the Molecule-to-Metal Transition,”Journal of the American Chemical Society, 18, 8459–8467 (2016)
Anthony Cirri, Alexey Silakov, Lasse Jensen, and Benjamin J. Lear, “Probing ligand-induced modulation of metallic states in small gold nanoparticles using conduction electron spin,” Physical Chemistry, Chemical Physics, 18, 25443–25451 (2016)
Steven R. Kennedy, Philip Weiss, Morgan N. Kozar, Hemant P. Yennawar, Puja Goyal, Lasse Jensen, Sharon Hammes-Schiffer, and Benjamin J. Lear, “Effect of Protonation upon Electronic Coupling in the Mixed Valence and Mixed Protonated Complex, [Ni(2,3-pyrazinedithiol)2],” Inorganic Chemistry, 55, 1433–1445 (2016)