Department of Chemistry and Biochemistry
Physical Chemistry Seminar Series

Professor Evan R. Williams – UC Berkeley
November 18, 2024 —2:00pm
Tykeson 140
Hosted by Jim Prell

Title: Overcoming Molecular Complexity One Ion at a Time

Heterogeneous materials can be challenging to analyze especially when the masses of individual components extend beyond 100 kDa.  With mass spectrometry, individual charge states produced by electrospray ionization can be difficult to resolve due to overlaps in m/z from other components or from adduction of salts or other non-specific molecular interactions.  One demonstrated solution to this problem of sample heterogeneity for high mass analytes is to measure the charge as well of the m/z of individual ions so that the mass of each ion can be determined without interference from other ions.  Single ion mass measurements have been performed with a variety of instrument types, but charge detection mass spectrometry with electrostatic ion traps have the advantage of virtually unlimited mass range, single charge accuracy, and the ability to make dynamic measurements.  A primary challenge is to acquire single ion data sufficiently rapidly to make this method practical.  Solutions to this challenge, as well as state of the art capabilities of charge detection mass spectrometry and applications to viral and nanoparticle analysis will be discussed. Results from experiments aimed at understanding the chemistry and physics of charged droplets will also be presented.

Department of Chemistry and Biochemistry
Organic-Inorganic-Materials Chemistry Seminar Series

Professor Nicholas D. Ball, Pomona College
November 1, 2024
3:00 pm, WIL 110
Hosted by the Alliance for Diversity in Science and Engineering (ADSE)

Title: Synthetic Strategies toward Fluorosulfurylation of  Organic Molecules and Lewis-Acid Catalyzed Sulfur-Fluoride Exchange (SuFEx)

Sulfur-fluoride exchange (SuFEx) chemistry is emerging as a promising synthetic tool in chemical biology, material science, and synthetic chemistry. In synthesis, sulfur (VI) fluorides show unique promise as synthons in organic chemistry due to their stability versus other sulfur (VI) halogen analogues. The key to adopting SuFEx chemistry is the development of efficient modes to synthesize and react to sulfur (VI) fluorides. Research initiatives employing Lewis acids, and transition-metal chemistry toward synthesizing sulfonyl fluorides will be described. New SuFEx methods that react a broad set of S(VI) fluorides with carbon, oxygen, and nitrogen-based nucleophiles towards structurally diverse S(VI) compounds will also be presented.

Our study introduces a novel SuFEx reaction that synthesizes nitrogen-based sulfonylated compounds from various S(VI) fluorides, mediated via a Lewis acidic calcium salt. This reaction, conducted under a unified set of reaction conditions, allows for coupling sulfonyl fluorides, fluorosulfates, and sulfamoyl fluorides with various amines. The result is the synthesis of a wide array of aryl and alkyl sulfonamides, sulfamides, and sulfamates in good to excellent yield. We will also discuss computational and NMR kinetic studies that aim to elucidate the mechanism of Ca-activation and the lessons learned from these mechanistic studies that have led to new catalytic SuFEx reactions that work across an array of Lewis acids.

Department of Chemistry and Biochemistry
Organic/Inorganic/Materials Seminar Series

Dirk M. Guldi, Friedrich Alexander University Erlangen-Nürnberg
October 4, 2024 ~ 3:00 pm, WIL 110
Hosted by Mike Haley

Title: Towards Adaptive Light Capture, Conversion, and Storage

The sun is an abundant and sustainable source of energy that is vital for the on-going energy transition. However, while abundant, the solar radiation reaching the earth’s surface covers a broad range of energies, from high-energy ultraviolet, through the visible region, to low-energy infrared. This poses significant challenges for efficient capturing and converting solar energy.

For photons with energies well-above the bandgap of the absorbing material, excess energy is lost predominantly by thermalization in the form of heat. In contrast, photons with energies below the optical bandgap are not absorbed at all. Even at peak efficiencies, both thermalization and sub-bandgap losses account for over 50% of incident solar power. Therefore, single-junction solar cells are limited to a maximum performance of 33%, which is known as the detailed balance limit. It is therefore imperative to find strategies to reduce thermalization and sub-bandgap losses to achieve efficiencies beyond the detailed balance limit. Here, down- and up-conversion processes could, theoretically, increase solar-energy conversion efficiencies beyond current limitations by reaching 39% and 49%, respectively. Additionally, the integration of down- and up-shifters with the aforementioned elements will aid in controlling light throughout the solar radiation spectrum, spanning from the ultraviolet up to the infrared.

The spectral conversion enables modifying the incident solar spectrum such that a better match is obtained with the wavelength-dependent conversion efficiency of, for example, the photoactive layer of photovoltaics. We thereby demonstrate to harness down- and/or up-converting or down- and/or up-shifting of the spectrum, meaning that the energy of photons is modified at demand to either lower or higher energy. Hereby, we systematically vary the electronic coupling in molecular dimers and oligomers to tune the dynamics of all relevant down- and up-conversion steps and, in turn, deciphering not only the full mechanisms of singlet-fission (SF) and triplet-triplet-annihilation up-conversion (TTA-UC), but also all bottlenecks enroute towards the conversion targets of 200% down-converted triplets at minimum driving forces and 50% up-converted singlets at maximum anti Stokes shifts. All of our down- and up-converters will be combined with complementary absorbers to round off the optimal spectral overlap across the solar spectrum by either down- or up-shifting of the spectrum. Crucially, we achieve this not only in solution, but also in the solid state with optimized arrangement and panchromatic absorption from 300 to 1000 nm.

Publications & Resources

Guldi Group, Friedrich-Alexander University

Dirk Guldi, Citations

Dirk Guldi, Electrochemical Society

Dirk Guldi, ResearchGate