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    Enantioenrichment of racemic BINOL by way of excited state proton transfer
    (Royal Society of Chemistry, 2019) Ayad, Suliman; Posey, Victoria; Das, Anjan; Montgomery, Jason M.; Hanson, Kenneth
    Here we report a method for enantioenriching BINOL using a chiral auxiliary and an excited state proton transfer (ESPT) event. Regardless of the starting enantiomeric excess (ee), after irradiation the solution reaches a photostationary state whose ee is dependent solely on the identity of the chiral auxiliary group. The enantio-enriched BINOL is easily recovered by cleaving the auxiliary group in mild conditions.
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    Mosaic-like Silver Nanobowl Plasmonic Crystals as Highly Active Surface-Enhanced Raman Scattering Substrates
    (The Journal of Physical Chemistry, 2015) Baca, Alfred J.; Baca, Joshua; Montgomery, Jason M.; Cambrea, Lee R.; Funcheon, Peter; Johnson, Linda; Moran, Mark; Connor, Dan
    We present a simple approach to creating a type of surface-enhanced Raman scattering (SERS) substrate composed of a mosaic-like structured Ag metal surface on nanobowl plasmonic crystals (NBPCs) formed by combining soft nanoimprinting and substrate (in situ) heating during metal deposition. This new type of sensor exploits the electromagnetic enhancement of localized surface plasmon resonances (LSPR) produced by a template nanostructured metal surface and surface plasmons (SP) in-between the gaps of the mosaic surface to create a highly SERS-active substrate. Our approach is simple, in that it implements low processing temperatures (200 °C) and does not require any postdeposition annealing or exposure to high temperature environments, enabling the use of mechanically flexible substrates. These SERS substrates exhibit higher SERS intensities in comparison to those obtained with the corresponding square array of smooth (room temperature metal deposition) nanobowl structures with similar spatial layouts. As an example toward an application, we demonstrate polychlorinated biphenyl (PCB-77) SERS detection using Ag mosaic NBPC substrates. Three-dimensional finite-difference time-domain (3D FDTD) simulations qualitatively capture the key features of these systems and suggest a route to the fabrication of optimized, highly efficient SERS substrates in silico.
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    Optimization of nanopost plasmonic crystals for surface enhanced Raman scattering
    (The Journal of Physical Chemistry, 2011) Baca, Alfred J.; Montgomery, Jason M.; Cambrea, Lee R.; Moran, Mark; Johnson, Linda; Yacoub, Jeanine; Truong, Tu T.
    We present experimental and theoretical studies of a type of Surface Enhanced Raman Scattering (SERS) substrate composed of a metal coated square array of nanopost structures formed via soft nanoimprinting. These SERS substrates exhibit higher SERS intensities in comparison to those obtained with the corresponding square array of nanowell structures with similar spatial layouts and demonstrate multiple analyte detection using SERS. Three-dimensional finite-difference time-domain (3D FDTD) simulations qualitatively capture the key features of these systems and suggest a route to the fabrication of optimized, highly efficient SERS substrates in silico. Collectively, the ease of fabrication, high sensitivities, and predictable responses suggest an attractive route to SERS substrates for portable chemical warfare agent detection, environmental monitors, and other applications.
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    Effect of pendant isophthalic acid moieties on the adsorption properties of light hydrocarbons in HKUST-1-like tbo -MOFs: Application to methane purification and storage
    (Royal Society of Chemistry, 2014) Belmabkhout , Youssef; Mouttaki, Hasnaa; Eubank, Jarrod F.; Guillerm, Vincent; Eddaoudi, Mohamed
    Equilibrium adsorption of methane (CH4), C2+ gases (ethane (C2H6), ethylene (C2H4), propane (C3H8), and propylene (C3H6)), and carbon dioxide (CO2) was measured on a series of tbo-MOFs (topological analogues of the prototypical MOF, HKUST-1, correspondingly dubbed tbo-MOF-1), which were developed via the supermolecular building layer (SBL) pillaring strategy. Specifically, tbo-MOF-2 and its isoreticular, functionalized analogue, tbo-MOF-2-{CH2O[Ph(CO2H)2]}2 (or tbo-MOF-3), which is characterized by pendant isophthalic acid moieties freely pointing into the cavities, were evaluated on the basis of potential use in methane storage and C2+/CH4 separation. The parent, tbo-MOF-2, showed high gravimetric and volumetric CH4 uptake, close to the U.S. Department of Energy (DOE) target for methane storage at 35 bar and room temperature. Though the presence of the pendant isophthalic acid moiety in the analogous compound, tbo-MOF-3, led to a decrease in total CH4 uptake, due mainly to the reduced size of the cavities, interestingly, it increased the affinity of the SBL-based tbo-MOF platform for propane, propene, ethane, and ethylene at low pressures compared with CH4, due additionally to the enhanced interactions of the highly polarizable light hydrocarbons with the isophthalic acid moiety. Using Ideal Adsorption Solution Theory (IAST), the predicted mixture adsorption equilibria for the C3H8/CH4, C3H6/CH4, C2H6/CH4, C2H4/CH4, and C3H8/CO2 systems showed high adsorption selectivity for C2+ over methane for tbo-MOF-3 compared with tbo-MOF-2. The high working storage capacity of tbo-MOF-2 and the high affinity of tbo-MOF-3 for C2+ over CH4 and CO2 make tbo-MOF an ideal platform for studies in gas storage and separation.
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    The design and optimization of plasmonic crystals for surface enhanced Raman spectroscopy using the finite difference time domain method
    (MDPI AG, 2018) Bigness, Alec; Montgomery, Jason M.
    We present computational studies of quasi three-dimensional nanowell (NW) and nanopost (NP) plasmonic crystals for applications in surface enhanced Raman spectroscopy (SERS). The NW and NP plasmonic crystals are metal coated arrays of cylindrical voids or posts, respectively, in a dielectric substrate characterized by a well/post diameter (D), relief depth (R D), periodicity (P), and metal thickness (M T). Each plasmonic crystal is modeled using the three-dimensional finite-difference time-domain (FDTD) method with periodic boundary conditions in the x- and y-directions applied to a computational unit cell to simulate the effect of a periodic array. Relative SERS responses are calculated from time-averaged electric field intensity enhancements at λ exc and λ scat or at λ mid via G SERS 4 = g 2 ( λ exc ) × g 2 ( λ scat ) or G mid 4 = g 4 ( λ mid ) , respectively, where g 2 = | E | 2 / | E 0 | 2 . Comparisons of G SERS 4 and G mid 4 are made to previously reported experimental SERS measurements for NW and NP geometries. Optimized NW and NP configurations based on variations of D, P, R D, and M T using G SERS 4 are presented, with 6× and 2× predicted increases in SERS, respectively. A novel plasmonic crystal based on square NP geometries are considered with an additional 3× increase over the optimized cylindrical NP geometry. NW geometries with imbedded spherical gold nanoparticles are considered, with 10× to 10 3 × increases in SERS responses over the NW geometry alone. The results promote the use of FDTD as a viable in silico route to the design and optimization of SERS active devices.