George C. Schatz

Northwestern University, Evanston, Illinois, United States

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Publications (719)3023.31 Total impact

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    ABSTRACT: High-performance solution-processed organic semiconductors maintain macroscopic functionality even in the presence of microscopic disorder. Here we show that the functional robustness of certain organic materials arises from the ability of molecules to create connected mesoscopic electrical networks, even in the absence of periodic order. The hierarchical network structures of two families of important organic photovoltaic acceptors, functionalized fullerenes and perylene diimides, are analyzed using a newly developed graph methodology. The results establish a connection between network robustness and molecular topology, and also demonstrate that solubilizing moieties play a large role in disrupting the molecular networks responsible for charge transport. A clear link is established between the success of mono and bis functionalized fullerene acceptors in organic photovoltaics and their ability to construct mesoscopically connected electrical networks over length scales of 10 nm.
    Proceedings of the National Academy of Sciences of the United States of America. 06/2014;
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    ABSTRACT: We present theory and experiments which describe charge transfer from the [Formula: see text] and a(1)Δg states of molecular oxygen and atomic and molecular cations. Included in this work are new experimental results for O2(a(1)Δg) and the cations O(+), CO(+), Ar(+), and [Formula: see text], and new theory based on complete active space self-consistent field method calculations and an extended Langevin model to calculate rate constants for ground and excited O2 reacting with the atomic ions Ar(+), Kr(+), Xe(+), Cl(+), and Br(+). The T-shaped orientation of the (X - O2)(+) potential surface is used for the calculations, including all the low lying states up to the second singlet state of the oxygen molecule [Formula: see text]. The calculated rate constants for both [Formula: see text] and O2(a(1)Δg) show consistent trends with the experimental results, with a significant dependence of rate constant on charge transfer exothermicity that does not depend strongly on the nature of the cation. The comparisons with theory show that partners with exothermicities of about 1 eV have stronger interactions with O2, leading to larger Langevin radii, and also that more of the electronic states are attractive rather than repulsive, leading to larger rate constants. Rate constants for charge transfer involving O2(a(1)Δg) are similar to those for [Formula: see text] for a given exothermicity ignoring the electronic excitation of the O2(a(1)Δg) state. This means (and the electronic structure calculations support) that the ground and excited states of O2 have about the same attractive interactions with ions.
    The Journal of chemical physics. 06/2014; 140(21):214307.
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    ABSTRACT: Herein we utilize on-wire lithography (OWL) to synthesize a composite plasmonic–semiconductor material composed of Au nanorod dimers embedded within anatase TiO2 sheets. We demonstrate that, despite the harsh conditions necessary to synthesize crystalline TiO2, the gapped nanostructures remain intact. Additionally, we show that the optical properties of these structures can be tailored via the geometric control afforded by the OWL process to produce structures with various gap sizes exhibiting different electric field intensities near the surface of the metal particles and that those fields penetrate into the semiconductor material. Finally, we show that this composite amplifies the electric field of incident light on it by a factor of 103, which is more that 750 times greater than the isotropic materials typically used for these systems.
    Chemistry of Materials. 06/2014; 26(12):3818–3824.
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    ABSTRACT: By introducing steric constraints into molecular compounds, it is possible to achieve atypical coordination geometries for the elements. Herein, we demonstrate that a titanium-oxo cluster [{Ti4(4-O)(2-O)2}(OPri)6(fdc)2], which possesses a unique edge-sharing Ti4O17 octahedron tetramer core, is stabilized by the constraints produced by two orthogonal 1,1′-ferrocenedicarboxylato (fdc) ligands. As a result, a square-planar tetracoordinate oxygen (ptO) can be generated. The bonding pattern of this unusual anti-van’t Hoff / Le Bel oxygen, which has been probed by theoretical calculations, can be described by two horizontally -bonded 2px and 2py orbitals along with one perpendicular non-bonded 2pz orbital. While the two ferrocene units are separated spatially by the ptO with an Fe•••Fe separation of 10.4 Å, electronic communication between them still takes place as revealed by the cluster’s two distinct one-electron electrochemical oxidation processes.
    Angewandte Chemie International Edition 06/2014; 2014. · 11.34 Impact Factor
  • Michael B. Ross, George C. Schatz
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    ABSTRACT: We use classical electrodynamics calculations to investigate the versatility and capability of aluminum and indium dimers with small gaps as ultraviolet plasmonic nanoantennas, focusing on the particle size and wavelength range that gives optimum near-field enhancement. We find that Al and In are highly capable plasmonic materials in the ultraviolet, even with the incorporation of Al2O3 shells on the Al spheres; however, Al is strongly influenced by quadrupole modes while In is not. Al is the optimal material in the deep-UV, while In is ideal in the near-UV and near-visible spectral regions. Unlike Au and Ag, Al and In are most effective with the lowest refractive index background media possible, with vacuum being ideal. Ag outperforms both Al and In red of 320 nm, but optimal surface-enhanced Raman spectroscopy enhancement factors are still substantial for Al and In, with peak |E|4 values (for dimers in vacuum with a 1 nm gap) determined to be: Al, 2.0 × 109 (at 204 nm); In, 1.2 × 109 (at 359 nm); Al/Al2O3, 1.2 × 107 (at 218 nm). For comparison, the optimal |E|4 for Au dimers is 2.8 × 1011 (at 723 nm) and for Ag is 1.3 × 1012 (at 794 nm), with background indices of 1.50 and 2.25, respectively. These data suggest that the continued exploration of Al and In as plasmonic materials could provide powerful opportunities in ultraviolet spectroscopic enhancement, fluorescence quenching, and cellular imaging.
    The Journal of Physical Chemistry C. 05/2014; 118(23):12506–12514.
  • Tao Yu, One-Sun Lee, George C Schatz
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    ABSTRACT: We have employed molecular dynamics simulations and quantum chemistry methods to study the structures and electronic absorption properties of a novel type of photonic nanowire gel constructed by the self-assembly of peptide amphiphiles (PAs) and the chromophore-(PPIX)Zn molecules. Using MD simulations, structures of the self-assembled fiber were determined with atomistic detail, including the distribution of chromophores along the nanofiber and the relative distances and orientations of pairs of chromophores. In addition, quantum chemistry calculations were used to determine the electronic structure and absorption properties of the chromophores in the fiber, so as to assess the capabilities of the nanofiber for photonics applications. The calculations show that the PA nanofiber provides an effective scaffold for the chromophores in which the chromophores form several clusters in which nearest neighbor chromophores are separated by less than 20 Å. The calculations also indicate that the chromophores can be in both the hydrophilic shell and hydrophobic core portions of the fiber. There are only small spectral shifts to the B-band of the porphyrins arising from the inhomogeneous micro-electronic environment provided by the fiber. However there are much stronger electronic interactions between nearby pairs of chromophores, leading to a more significant red-shift of the B-band that is similar to what is found in the experiments, and to significant excitonic coupling that is seen in circular dichroism spectra. This electronic interaction between chromophores associated with the PA nanofiber structure is crucial to future applications of these fibers for light-harvesting applications.
    The Journal of Physical Chemistry A 04/2014; · 2.77 Impact Factor
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    ABSTRACT: We report the large-area assembly of anisotropic gold nanoparticles into lithographically defined templates with control over their angular position using a capillary force-based approach. We elucidate the role of the geometry of the templates in the assembly of anisotropic nanoparticles consisting of different shapes and sizes. These insights allow us to design templates that immobilize individual triangular nanoprisms and concave nanocubes in a shape-selective manner and filter undesired impurity particles from a mixture of triangular prisms and other polyhedra. Furthermore, by studying the assembly of two particles in the same template, we elucidate the importance of interparticle forces in this method. These advances allow for the construction of face-to-face and edge-to-edge nanocube dimers as well as triangular nanoprism bowtie antennas. As an example of the fundamental studies enabled by this assembly method, we investigate the surface-enhanced Raman scattering (SERS) of face-to-face concave cube dimers both experimentally and computationally and reveal a strong polarization dependence of the local field enhancement.
    Nano Letters 03/2014; · 13.03 Impact Factor
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    ABSTRACT: Trinucleotide and tetranucleotide repeat disorders are genetic inheritable diseases caused by mutations in DNA where the repeats in certain genes exceed the normal size. Once the repeats are transcribed, mRNA folds into a hairpin with repeating CXG (X = C, A, G, U) or CCUG motifs, which either attract cytoplasmic multiprotein complexes or translate into toxic polyQ proteins and cause the disease. These mRNA repeats have 1×1 or 2×2 internal loops, which make them ideal targets for pharmacologic development. Yet, the dynamic nature of RNA loops presents a significant challenge to obtaining reasonable predictions for targeting RNA repeats with small molecules. Two important results from our recent studies provide a point of entry into this challenging problem. First, we found that 1×1 AA internal loops in RNA CAG repeat expansions are dynamic and can form multiple different stable conformations; and second, we found that targeting 1×1 UU and 2×2 CU/UC internal loops with a small molecules produced complex structural changes in the RNA loop conformations with lowest free energy structures corresponding to one of the local minimum states predicted for 1×1 AA internal loops. These results suggest that RNA internal loops have multiple different free energy minimum states, which could be dominated with small molecules upon binding.
    ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, Dallas, Texas; 03/2014
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    ABSTRACT: Many naturally occurring peptides containing cationic and hydrophobic domains have evolved to interact with mammalian cell membranes and have been incorporated into materials for non-viral gene delivery, cancer therapy or treatment of microbial infections. Their electrostatic attraction to the negatively charged cell surface and hydrophobic interactions with the membrane lipids enable intracellular delivery or cell lysis. Although the effects of hydrophobicity and cationic charge of soluble molecules on the cell membrane are well known, the interactions between materials with these molecular features and cells remain poorly understood. Here we report that varying the cohesive forces within nanofibres of supramolecular materials with nearly identical cationic and hydrophobic structure instruct cell death or cell survival. Weak intermolecular bonds promote cell death through disruption of lipid membranes, while materials reinforced by hydrogen bonds support cell viability. These findings provide new strategies to design biomaterials that interact with the cell membrane.
    Nature Communications 02/2014; 5:3321. · 10.02 Impact Factor
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    ABSTRACT: Abstract The development of new sensitive methods for the detailed collection of conformational and morphological information about amyloids is crucial to elucidating critical questions regarding the aggregation processes in neurodegenerative diseases. The combined approach of two-photon and time-resolved fluorescence spectroscopy described in this report interrogates the early conformational dynamics seen in soluble oligomers of amyloid- 1-42. Two-photon absorption concentration-dependent aggregation studies show enhanced sensitivity toward conformational changes taking place in the secondary structure of the amyloid peptide as aggregation proceeds. Fluorescence lifetimes and changes in anisotropy values indicate Förster-type energy transfer occurring as a function of aggregation state. The sensitivity of our two-photon methodology is compared to circular dichroism (CD) spectroscopy and the results indicate that the two-photon absorption cross-section method exhibits superior sensitivity. A theoretical model is developed which together with electronic structure calculations explains the change in cross-section as a function of aggregation in terms of interacting transition dipoles for aggregates showing stacked or parallel structures. This suggests that the two-photon method provides a sensitive alternative to CD while avoiding many of the inherent challenges particular to CD data collection. The implication of this is significant, as it indicates that a two-photon based technique used in conjunction with time-resolved fluorescence may be able to reveal answers to conformational questions about Amyloid- 1-42 which are presently inaccessible with other techniques.
    The Journal of Physical Chemistry B 02/2014; · 3.61 Impact Factor
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    ABSTRACT: Detailed computational and experimental studies reveal the crucial role that hydrophobic interactions play in the self-assembly of small molecule-DNA hybrids (SMDH) into cyclic nanostructures. In aqueous environments, the distribution of the cyclic structures (dimer or higher-order structures) greatly depends on how well the hydrophobic surfaces of the organic cores in these nanostructures are minimized. Specifically, when the cores are attached to the 3'-ends of the DNA component strands, they can insert into the minor groove of the duplex that forms upon self-assembly, favoring the formation of cyclic-dimers. However, when the cores are attached to the 5'-ends of the DNA component strands, such insertion is hindered, leading to the formation of higher-order cyclic structures. These computational insights are supported by experimental results that show clear differences in product distributions and stabilities for a broad range of organic core-linked DNA hybrids with different linkage directions and flexibilities.
    The Journal of Physical Chemistry B 02/2014; · 3.61 Impact Factor
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    ABSTRACT: We show how a complex Snell's law can be used to describe the refraction of surface plasmon polaritons (SPPs) at an interface between two metals, validating its predictions with 3-D electro-dynamics simulations. Refraction gives rise to peculiar SPP features including inhomogeneities in the waveform and dispersion relations that depend on the incident wave and associated mate-rial. These features make it possible to generate SPPs propagating away from the interface with significant confinement normal to the propagation direction. We also show that it is possible to encode optical properties of the incident material into the refracted SPP. These consequences of metal-metal SPP refraction provide new avenues for the design of plasmonics-based devices.
    01/2014;
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    ABSTRACT: Hollow spherical gold nanoparticle superstructures with tunable sizes (~40 nm, ~70 nm and ~150 nm) and visible to near-infrared surface plasmon resonances (545 nm, 670 nm, and 740 nm) are prepared using a single peptide conjugate, C6-AA-PEPAu as the structure-directing agent. Computational models are developed to understand their optical properties.
    Nanoscale 01/2014; · 6.23 Impact Factor
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    Michael B Ross, Martin G Blaber, George C Schatz
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    ABSTRACT: The a priori ability to design electromagnetic wave propagation is crucial for the development of novel metamaterials. Incorporating plasmonic building blocks is of particular interest due to their ability to confine visible light. Here we explore the use of anisotropy in nanoscale and mesoscale plasmonic array architectures to produce noble metal-based metamaterials with unusual optical properties. We find that the combination of nanoscale and mesoscale anisotropy leads to rich opportunities for metamaterials throughout the visible and near-infrared. The low volume fraction (<5%) plasmonic metamaterials explored herein exhibit birefringence, a skin depth approaching that of pure metals for selected wavelengths, and directionally confined waves similar to those found in optical fibres. These data provide design principles with which the electromagnetic behaviour of plasmonic metamaterials can be tailored using high aspect ratio nanostructures that are accessible via a variety of synthesis and assembly methods.
    Nature Communications 01/2014; 5:4090. · 10.02 Impact Factor
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    ABSTRACT: We show analytically and with rigorous computa-tional electrodynamics how inhomogeneous surface plasmon polaritons (ISPPs) can be generated by refraction of ordinary SPPs at metal−metal interfaces. ISPPs, in contrast with SPPs, propagate and decay in different directions and can therefore exhibit significantly different intensity patterns. Our analytical arguments are based on a complex generalization of Snell's law to describe how SPPs moving on one metal surface are refracted at an interface with a second, different metal surface. The refracted waveform on the second metal is an ISPP. Under suitable circumstances the decay of an ISPP can be almost perpendicular to the propagation direction, leading to significant confinement. It is also found that ISPPs on the second metal can retain information about the SPPs on the first metal, a phenomenon that we term "dispersion imprinting". The complex Snell's law predictions are validated with 3-D finite-difference time-domain simulations, and possible means of experimentally observing ISPPs are suggested. The idea of ISPPs and how they result from refraction may expand the potential for designing the propagation and dispersion features of surface waves in general, including surface phonon polaritons, surface magnons, and guided waves in metamaterials. S urface plasmon polaritons (SPPs) are surface waves created by coupling light into charge-density oscillations at a metal−dielectric interface that allow optical energy and information to be strongly confined to a two-dimensional surface. 1−7 Systems that permit the excitation of SPPs can exhibit interesting and unexpected optical properties, including extraordinary optical transmission 8 and superlensing. 9−11 Such properties are relevant to a wide range of applications including imaging and sensing 12−16 and optoelectronics, 17−20 so controlling and manipulating SPP propagation is a major goal of nanophotonics research. 21,22
    ACS Photonics. 01/2014;
  • Fredy W Aquino, George C Schatz
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    ABSTRACT: We present an implementation of a TD-DFT linear response module in NWChem for unrestricted DFT calculations and apply it to the calculation of resonant Raman spectra in open-shell molecular systems using the short-time approximation. The new source code was validated and applied to simulate Raman spectra on several doublet organic radicals (e.g. benzyl, benzosemiquinone, TMPD, trans-stilbene anion and cation, methyl viologen) and the metal complex copper phthalocyanine. We also introduce a divide-and-conquer approach for the evaluation of polarizabilities in relatively large systems (e.g. copper phthalocyanine). The implemented tool gives comparisons with experiment that are similar to what is commonly found for closed-shell systems, with good agreement for most features except for small frequency shifts, and occasionally large deviations for some modes that depend on the the molecular system studied, experimental conditions not being accounted in the modelling such as solvation effects and extra solvent-based peaks, and approximations in the underlying theory. The approximations used in the quantum chemical modelling include: i) choice of exchange-correlation functional and basis set; ii) harmonic approximation used in the frequency analysis to determine vibrational normal modes; iii) short-time approximation (omission of nuclear motion effects) used in calculating resonant Raman spectra.
    The Journal of Physical Chemistry A 12/2013; · 2.77 Impact Factor
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    ABSTRACT: The reactive uptake and ionization of sodium atoms in glycerol were investigated by gas-liquid scattering experiments and ab initio molecular dynamics (AIMD) simulations. A nearly effusive beam of Na atoms at 670 K was directed at liquid glycerol in vacuum, and the scattered Na atoms were detected by a rotatable mass spectrometer. The Na velocity and angular distributions imply that all impinging Na atoms that thermally equilibrate on the surface remain behind, likely ionizing to e(-) and Na(+). The reactive uptake of Na atoms into glycerol was determined to be greater than 75%. Complementary AIMD simulations of Na striking a 17-molecule glycerol cluster indicate that the glycerol hydroxyl groups reorient around the Na atom as it makes contact with the cluster and begins to ionize. Although complete ionization did not occur during the 10 ps simulation, distinct correlations can be observed between the extent of ionization, separation between Na(+) and e(-), solvent coordination, and binding energies of the Na atom and electron. The combination of experiments and simulations indicates that Na-atom deposition provides a low-energy pathway for generating solvated electrons in the near-interfacial region of protic liquids.
    Journal of the American Chemical Society 12/2013; · 10.68 Impact Factor
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    ABSTRACT: Understanding of atomic interactions between constituents is critical to the design of high-performance nanocomposites. Here, we report an experimental-computational approach to investigate the adhesion energy between as-produced arc discharge multiwalled carbon nanotubes (MWCNTs) and graphene. An in situ scanning electron microscope (SEM) experiment is used to peel MWCNTs from graphene grown on copper foils. The force during peeling is obtained by monitoring the deflection of a cantilever. Finite element and molecular mechanics simulations are performed to assist the data analysis and results interpretation. A finite element analysis of the experimental configuration is employed to confirm the applicability of Kendall's peeling model to obtain the adhesion energy. Molecular mechanics simulations are used to estimate the effective contact width at the MWCNT-graphene interface. The measured surface energy is γ = 0.20 ± 0.09 J-m(-2) or γ = 0.36 ± 0.16 J-m(-2), depending on the assumed conformation of the tube cross section during peeling. The scatter in the data is believed to result from an amorphous carbon coating on the MWCNTs, observed using transmission electron microscopy (TEM), and the surface roughness of graphene as characterized by atomic force microscopy (AFM).
    ACS Nano 12/2013; · 12.03 Impact Factor

Publication Stats

16k Citations
3,023.31 Total Impact Points

Institutions

  • 1977–2014
    • Northwestern University
      • • Department of Chemistry
      • • Department of Mechanical Engineering
      Evanston, Illinois, United States
  • 2011–2013
    • University of Maryland, College Park
      • Department of Chemistry and Biochemistry
      College Park, MD, United States
    • Chapman University
      Orange, California, United States
    • University of North Texas
      Denton, Texas, United States
  • 1975–2011
    • California Institute of Technology
      • • Division of Chemistry and Chemical Engineering
      • • Arthur Amos Noyes Laboratory of Chemical Physics
      Pasadena, CA, United States
  • 2005–2010
    • Montana State University
      • Department of Chemistry & Biochemistry
      Bozeman, MT, United States
    • Chalmers University of Technology
      • Department of Applied Physics
      Göteborg, Vaestra Goetaland, Sweden
    • Université de Technologie de Troyes
      • Laboratoire de Nanotechnologie et d’Instrumentation Optique (LNIO)
      Troyes, Champagne-Ardenne, France
    • National Academy of Sciences of Ukraine
      Kievo, Kyiv City, Ukraine
  • 2009
    • University of Namur
      Namen, Walloon Region, Belgium
    • Cornell University
      Ithaca, New York, United States
    • University of Victoria
      • Department of Chemistry
      Victoria, British Columbia, Canada
  • 2008–2009
    • Delft University Of Technology
      • Department of Chemical Engineering
      Delft, South Holland, Netherlands
    • University of Illinois, Urbana-Champaign
      • Department of Biochemistry
      Urbana, IL, United States
    • Pennsylvania State University
      • Department of Chemistry
      University Park, MD, United States
    • Tulane University
      • Department of Chemistry
      New Orleans, LA, United States
    • University of Colorado Colorado Springs
      Colorado Springs, Colorado, United States
  • 2007–2008
    • Kangwon National University
      • Department of Chemistry
      Syunsen, Gangwon, South Korea
    • Max Planck Institute for Biophysical Chemistry
      Göttingen, Lower Saxony, Germany
  • 1992–2008
    • Northwest University
      Evanston, Illinois, United States
  • 1982–2008
    • Argonne National Laboratory
      Lemont, Illinois, United States
  • 1977–2008
    • Massachusetts Institute of Technology
      • Department of Chemistry
      Cambridge, Massachusetts, United States
  • 2004–2007
    • Pusan National University
      • • Department of Nanomaterials Engineering
      • • Department of Food Science and Technology
      Pusan, Busan, South Korea
    • Spectral Sciences Incorporated
      Burlington, Massachusetts, United States
  • 2005–2006
    • University of South Carolina
      • Chemistry and Biochemistry
      Columbia, SC, United States
    • Stanford University
      • Department of Chemistry
      Stanford, CA, United States
  • 2003
    • Institute for Molecular Science
      Okazaki, Aichi, Japan
  • 1986–1995
    • The University of Manchester
      • School of Chemistry
      Manchester, ENG, United Kingdom