Focus on Scholarly Communication
Presented by the Royal Society of Chemistry and the University of Chicago Department of Chemistry"Meet the editor" event, hosted by Dmitri Talapin
Lea Nienhaus, Massachusetts Institute of Technology
From Imaging Excitons at the Nanoscale to Emerging Device ApplicationsUnderstanding light-induced processes in materials is critical for tailoring their optical and electronic properties to applications in chemical conversion, light harvesting, or energy transfer. Nanomaterials are prime candidates to study light-matter interactions on both the single-particle and the ensemble level. However, they are prone to defects which can be detrimental to their function in optoelectronic devices. Furthermore, many optoelectronic and photocatalytic systems are based on hybrid interfaces combining both inorganic and organic materials. The exact energy transfer mechanism at these hybrid interfaces is often obscure, particularly when both the macroscopic donor and acceptor materials consist of many separately interacting moieties. Here, I describe the detailed photophysics of a PbS nanocrystal-based light-harvesting device, and further demonstrate a technique for single-particle visualization of absorption in various nanomaterials.
I present exchange-mediated spin-triplet exciton transfer from semiconducting PbS nanocrystals to the triplet state of the organic molecule rubrene. Diffusion-mediated triplet-triplet annihilation in rubrene generates higher-energy emissive spin-singlet states, and shows promise in sub-bandgap sensitization of silicon. We combine transient photoluminescence spectroscopy with a kinetic model to unravel the underlying photophysics of the relevant energy transfer processes occurring in the upconverting device.
To further investigate light-harvesting at the nanoscale, I employ single molecule absorption detected by scanning tunneling microscopy. This technique is based on a change in the local density of states upon absorption, and thus visualizes the localized excitation. Taking advantage of Stark shifts caused by the electric field in the STM, different energy levels can be shifted into resonance with the excitation wavelength.
Professor Tohru Fukuyama, Nagoya University
Synthetic Studies on TetrodotoxinTetrodotoxin (TTX) is one of the most famous marine natural products, which is found most notably in the liver and ovary of puffer fish. It is the toxin responsible for the fatal food poisoning caused by improperly cooked puffer fish in Japan. This compound also serves as an important biochemical tool in neurophysiology since it exhibits neurotoxicity by selectively blocking sodium channels of excitable cell membranes. Despite its relatively small molecular size, TTX possesses eight contiguous stereogenic centers in its polyfunctionalized dioxaadamantane skeleton including an orthoester and a guanidine moieties. This fascinating molecule has been a popular target for many synthetic chemists although only a few successful total syntheses have been reported to date. We initiated our synthetic studies on TTX in the hope of identifying the exact location of sodium channels where TTX blocks. Recent progress of our approach will be discussed in the lecture.
IME Distinguished Colloquium Series: Rachel Segalman, UC Santa Barbara
Dr. Ryan Hadt, Argonne National Laboratory,
Structure/Function Correlations Over Heterogeneous Catalysis and Bioinorganic ChemistryThis talk covers recent combinations of spectroscopy and theory to develop relationships between molecular structure and function within specific areas of heterogeneous catalysis and bioinorganic chemistry as well as areas of their intersection. Focus within heterogeneous catalysis is on the formation, characterization and reactivity of high-valent intermediates involved in the chemistries of alternative fuel (e.g., the oxygen evolution reaction and the conversion of methane to methanol). The characterization of these intermediates allows for a direct correlation between active sites in heterogeneous catalysis and bioinorganic chemistry. Additional focus within bioinorganic chemistry is on demonstrating, understanding and quantifying entatic states (in the electronic ground state) and their contributions to controlling the function of electron transfer active sites. These concepts are further extended to the reactivity of transition metal excited states (e.g., copper photosensitizers). Lastly, the nature of the entatic state is defined in detail for cytochrome c, with emphasis on understanding the protein contribution to the active site Fe–S(Met) bond strength and how the energetics of the local protein fold allow for bifunctionality in energy transduction (electron transfer) and apoptosis (lipid peroxidation).
Marco Allodi PhD, Department of Chemistry, University of Chicago
Visualizing Chemical Dynamics Across Nanoscale Interfaces
Heinrich Jaeger, University of Chicago
Nick Bultinck, Princeton University
Tensor network trial wave functions for topological phasesThe construction of trial wave functions has proven itself to be very useful for understanding strongly interacting quantum many-body systems. Two famous examples of such trial wave functions are the resonating valence bond state proposed
by Anderson and the Laughlin wave function, which have provided an (intuitive) understanding of respectively spin liquids and fractional Quantum Hall states. Tensor network states are another, more recent, class of such trial wave functions which are based on entanglement properties of local, gapped systems. In this talk I will discuss the use of tensor network states for topological phases, and what we can learn from this approach. I will consider one- and two-dimensional systems, consisting of both spins and fermions. The focus will be on the different connections that can be made using tensor networks, such as connecting theory to numerics, and physical properties to ground state entanglement.