Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session F26: Journal of Chemical Physics Editor's Choice AwardsInvited Live Prize/Award Undergrad Friendly
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Sponsoring Units: DCP Chair: Amy Mullin, University of Maryland, College Park |
Tuesday, March 16, 2021 11:30AM - 12:06PM Live |
F26.00001: Unraveling the structure and dynamics of molecules at work Invited Speaker: Jochen Küpper Observing molecules in action through the recording of “molecular movies”, i. e., their spatiotemporal evolution during chemical dynamics, with atomic spatial and temporal resolution could revolutionize our understanding of the molecular sciences. Wel build upon our approaches to prepare highly controlled samples that enable advanced imaging methods of individual molecular species and directly in the molecular frame. Here, I will discuss the application of diffractive imaging for the recording of such movies with few-picometer and few-femtosecond resolution. Furthermore, I will present examples of UV-induced photochemical dynamics and the path toward the atomically resolved movies of these reactions. |
Tuesday, March 16, 2021 12:06PM - 12:42PM Live |
F26.00002: Evidence for laser-induced homogeneous oriented ice nucleation revealed via pulsed x-ray diffraction Invited Speaker: Iftach Nevo The induction of homogeneous and oriented ice nucleation has to date not been achieved. |
Tuesday, March 16, 2021 12:42PM - 1:18PM Live |
F26.00003: Tip-Enhanced Raman Spectroscopy: Chemical Analysis with Nanoscale to Angstrom Scale Resolution Invited Speaker: Nan Jiang Fundamental understandings of chemistry and physical properties at the nanoscale enables the rational design of interface-based systems. Surface interactions underlie numerous technologies ranging from catalysis to organic thin films to biological systems. Since surface environments are especially prone to heterogeneity, it becomes crucial to characterize these systems with spatial resolution sufficient to localize individual active sites or defects. Spectroscopy presents as a powerful means to understand these interactions, but typical light-based techniques lack sufficient spatial resolution. This talk describes a new sub-nanoscale spectroscopic technique, tip-enhanced Raman spectroscopy (TERS), with a focus on developments that reveal the intricacies of adsorbate-adsorbate/ adsorbate−substrate interactions. We have designed a series of TERS experiments to obtain chemical information for individual molecules with high precision. We were the first to differentiate adjacent regio-isomers that are nearly identical in their structures by using their unique vibrational fingerprints obtained with TERS at a spatial resolution of 8 Å, providing significant insights into the chemical properties and intermolecular interactions of a molecular heterojunction. Using our methods, we can also characterize the binding configurations of non-planar organic molecules that result in multiple self-assemblies on the same or different substrates, providing insight into highly localized chemical effects. |
Tuesday, March 16, 2021 1:18PM - 1:54PM Live |
F26.00004: Plasmon enhanced second harmonic generation by plasmonic arrays strongly coupled to quantum emitters Invited Speaker: Maxim Sukharev Optical properties of periodic arrays of nanoholes of a triangular shape with experimentally realizable parameters are examined in both linear and nonlinear regimes. By utilizing a fully vectorial three-dimensional approach based on the nonlinear hydrodynamic model describing metal coupled to Maxwell’s equations and Bloch equations for molecular emitters, we analyze linear transmission, reflection, and nonlinear power spectra. Rigorous numerical calculations demonstrating second and third harmonic generation by the triangular hole arrays are performed. It is shown that both the Coulomb interaction of conduction electrons and the convective term contribute on equal footing to the nonlinear response of metal. It is demonstrated that the energy conversion efficiency in the second harmonic process is the highest when the system is pumped at the localized surface plasmon resonance. When molecular emitters are placed on a surface of the hole array line shapes, the second harmonic signal exhibits three peaks corresponding to second harmonics of the localized surface plasmon mode and upper and lower polaritonic states. |
Tuesday, March 16, 2021 1:54PM - 2:30PM Live |
F26.00005: Tailoring interchromophore interactions for triplet pair production and separation in molecular assemblies Invited Speaker: Justin Johnson We report a library of molecules coupled to each other with tunable strengths and geometries to investigate the fundamental properties of spin-entangled triplet pairs, and further to evaluate the evolution toward independent triplets or spin-polarized quintet states. A system composed of perylene oligomers leverages the flexibility of a covalent phenylakynyl bridge to effectively "gate" multi-chromophore delocalization in the singlet excited state and localization in the triplet state to produce long-lived independent triplets with relatively high efficiency. Transient spectroscopy and calculations support the notion of a delocalized excitation in the planar excited state and subsequent picosecond-scale torsional dynamics that isolates triplets. The triplet yield depends strongly on the number of chromophores, rising from a few percent for the dimer to > 30% for the tetramer. The additional accessible isolated triplet configurations enable the formation of product states despite relatively large singlet fission endothermicity. |
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