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June 21st, 2022 Webinar Speakers

Our next webinar will take place via the internet on Tuesday June 21st at 10 AM EDT/3 PM BST. Sign up on our mailing list to receive the Zoom link!

We hope to see/hear from you all at one of our sessions or as one of the next speakers. If you are an early career scientist and would like to present your research, don't hesitate to submit an abstract today! For now, please learn more about our current speakers and their research below. We also thank the generous support from Cell Reports Physical Science, Merck, Janssen, and the Royal Society of Chemistry.

Our featured speakers this week are Rebecca Kehner (Graduate Student, Baylor University, USA), and Dr Ricardo Javier Vázquez (Postdoctoral Researcher, National University of Singapore, Singapore).


REBECCA KEHNER (on Twitter @RebeccaKehner)

Biography: I completed my B.S. in Chemistry from Kent State University in 2019, conducting research under Dr. Jeffrey Mighion. After briefly working at a pharmaceutical company, I moved to Waco, Texas to pursue my PhD under Dr. Liela Romero at Baylor University. I am currently finishing my second year of graduate school and recently became a PhD candidate. In the Romero group, I focus on developing new methods catalyzed by zirconium hydrides and studying these novel reaction mechanisms.

Title of Talk: "Expanding Zirconium Hydride Catalysis: In Situ Generation and Turnover of Zirconium Hydride Catalysts"

Abstract: Cp2ZrHCl (commonly referred to as Schwartz’s reagent) is widely used in organic synthesis for the hydrozirconation of various π-systems. Zirconium hydrides are almost exclusively employed as stoichiometric reagents rather than as metal hydride catalysts, despite their orthogonal reactivity in comparison to other late transition metal hydrides. We have developed a novel method for the mild in situ generation and turnover of Schwartz-like zirconium hydride catalysts, using only 2.5-5 mol % of the zirconocene dichloride precatalyst in combination with hydrosilane as the stoichiometric reductant. This method is exceptionally air- and moisture-tolerant and a wide variety of carbonyl- containing substrates are diastereo- and chemoselectively reduced with up to 92% yield and >20:1 dr. These findings and accompanying mechanistic observations serve as the foundation for future developments in zirconium hydride catalysis.

DR RICARDO JAVIER VASQUEZ (on Twitter @SantosFora)

Biography: Ricardo Javier Vázquez is a Puerto Rican emerging Organic Material Scientist and aspiring professor. He obtained his Ph.D. from the University of Michigan, Ann Arbor, where he used multiple time-resolved spectroscopic tools to understand the excited state dynamics of optoelectric materials. Ricardo is currently a postdoctoral fellow at the National University of Singapore, working on unlocking molecular features in conjugated polyelectrolytes to obtain unprecedented physico-electrochemical properties. Ricardo is a 2022 PMSE future faculty honoree and wants to develop the next-generation conjugated polyelectrolytes for energy harvesting, conversion, and storage applications by combining synthesis and time-resolved spectroscopy for his independent career.

Title of Talk: "Understanding the Excited State Dynamics of Organic Chromophores with Thermally Activated Delayed Fluorescence Characteristics"

Abstract: Thermally activated delayed fluorescence (TADF) is the idea that thermal energy can convert dark triplets into emissive singlets. We can used time-resolved spectroscopy to characterized the excited state dynamics of molecules designed to have TADF characteristics. Consequently, we developed a new optical method to determine the rate of reverse intersystem crossing (krISC) in TADF organic chromophores using time-resolved transient absorption spectroscopy. We successfully correlated the krISC of the TADF-chromophores with device performance. Specifically, we focused on the external quantum efficiency (ηEQE) and the stability of the device at high brightness levels. It is believed that by obtaining a large krISC one may reduce the possibility of triplet–triplet annihilation (TTA) and increase the long-term stability of organic light emitting diodes (OLEDs) devices at high brightness levels (ηEQE roll-off). In this contribution, we investigate the photophysical mechanism in a series of TADF-chromophores based on carbazole or acridine derivatives as donor moieties, and triazine or benzonitrile derivatives as the acceptor moieties. We found a relationship between large krISC values and high ηEQE values at low operating voltages for the TADF-chromophores investigated. In addition, those chromophores with a larger krISC illustrated a smaller ηEQE roll-off (higher stability) at high operating voltages. These features are beneficial for superior OLEDs performing devices. Contrarily, we found that if a chromophore has a krISC ≤ 105s–1 its ηEQE is ≤5%. Such a small krISC suggests that there is no TADF effect operating in these organic systems and the molecule is not efficient in harvesting triplet excitons. Emission lifetime-based methodologies for determining the krISC were included for comparison but failed to predict the devices performance of the investigated TADF-chromophores to the same extent of our proposed methodology.

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