General

Organic Chemistry Seminar: Dr. Richard Hark, Yale

Mon, 2018-09-17 12:00 - 13:00
Speaker: 

Dr. Richard Hark

"Preparation, Passion and Serendipity: Reflections on an Unfinished, Non-Traditional Career in Chemistry"

- "What do you want to be when you grow up?” is a question that is not directed solely to young children. Undergraduate and graduate students may wonder at times what they will do with their chemistry degree after graduation. In this seminar, the speaker will publicly confess that he is still trying to find the answers, even after a twenty-five-year career as a chemistry professor at liberal arts colleges. Though each person has to figure this out for themselves, the talk will provide some useful observations and general advice as Dr. Hark shares examples of how his training as a synthetic organic chemist at Penn provided the foundation on which to build an interesting and fulfilling, albeit somewhat non-traditional career.  Interspersed in the presentation will be examples of his broad research interests that include synthetic and analytical work in the fields of chemistry, forensics, geochemistry and conservation science.
Location: 

Carol Lynch Lecture Hall

Chemistry Complex

Host: Dr. Joullie

inquiries rvargas@sas.upenn.edu

Inorganic Chemistry Seminar: Dr. Michael Nippe, Texas A& M University

Tue, 2019-03-05 12:00 - 13:00
Speaker: 

Dr. Michael Nippe

Location: 

Carol Lynch lecture Hall

Chemistry Complex

Attached Document: 

 

"Taking Inspiration From Bulk: Molecular Electrocatalysis and Magnetization Dynamics of Heterometallic Lanthanide – Transition Metal Complexes"

 

Inorganic Chemistry Seminar: Dr.Linda Doerrer, Boston University

Tue, 2018-11-27 12:00 - 13:00
Speaker: 

Dr. Linda Doerrer

 

Title:  Teflon Coated Compounds and Their Chemistries

  Complexes surrounded by perfluorinated ligands have noticeably different physical and chemical properties than their non-fluorinated analogs.  Fluorinated ligands are well-known for their oxidative stability, and therefore make tempting targets for investigations in oxidative catalysis.  Our group has prepared a large family of first-row transition metal complexes of monodentate fluorinated alkoxide and aryoxide ligands, with the general form [M(ORF)n]m-.  These fluorinated ligands are the electronic equivalent of fluoride, based on spectrochemical studies and ligand field comparisons, but are quite distinct from [MFn]m- complexes in solubility, hydrolytic stability, and nuclearity.  More recently we have extended our investigations into bidentate systems, namely that of the perfluoropinacolate ligand.  This ligand endows its complexes with the same general characteristics as the monodentate systems investigated previously, with some additional new features as well.  In the [M(pinF)n]m- family, numerous members are air-stable and water soluble.  This talk will give an overview of our past work in homoleptic 3d metal complexes with monodentate perfluorinated ligands, and then move into published and unpublished work on perfluoropinacolate complexes.  Most recent highlights include some extraordinarily rare electronic structures, such as an S = 1 Co(III) complex, and unusual Sn(IV) and Sn(II) species. 
Location: 

Carol Lynch Lecture Hall

Chemistry Complex

Host: Dr.Schelter

inquiries rvargas@sas.upenn.edu

Inorganic Chemistry Seminar: Dr. Skye Fortier, University of Texas- El Paso

Tue, 2018-10-09 12:00 - 14:00
Speaker: 

Dr. Skye Fortier

"Metastable Metal Complexes Supported by Guanidinate Ligands"

-In this talk, we describe the chemistry of "metastable" iron and titanium complexes supported by N-donor ligands.  We have synthesized a "super bulky" guanidinate that provides kinetic stabilization to reactive metal fragments.  To this end, our efforts to synthesize and isolate complexes containing Fe=O/Fe≡N functionalities are discussed.  Additionally, we detail our work with titanium supported by guanidinate and imidazolin-2-iminato ligands and describe its reduction chemistry. For example, we have synthesized electron-rich titanium complexes, that when reduced by two-electrons, give access to Ti(II) synthons.  These Ti(II) platforms are highly reducing and exhibit unique reactivity. For instance, we observe oxidative-addition of C(sp3)-H bonds which enables catalytic transfer hydrogenation of cyclic olefins.  This reactivity and more will be presented.

Location: 

Carol Lynch Lecture Hall

 Chemistry Complex

Host: Mindiola

inquiries rvargas@sas.upenn.edu

Inorganic Chemistry Seminar: Dr. Laura Gagliardi, University of Minnesota

Tue, 2019-02-12 12:00 - 13:00
Speaker: 

Dr. Laura Gagliardi

Location: 

Carol Lynch Lecture Hall

Chemistry Complex

"Electronically Excited States and Transition-Metal Containing Syste

RESCHEDULED: Inorganic Chemistry Seminar: Dr. Markus Ribbe, UCI

Tue, 2018-09-18 12:00 - 13:00
Speaker: 

Dr. Markus Ribble

Seminar Rescheduled 5/7/2019

 

"Nitrogenase M-Cluster Assembly:"


"Tracing the ‘9th Sulfur’ of the Nitrogenase Cofactor via a Semi-Synthetic Approach"

"The  M-cluster  is  the  active  site  of  nitrogenase  that  contains  an  8Fe-core  assembled  via coupling and rearrangement  of  two [Fe4S4]  clusters  concomitant  with  the  insertion  of  an interstitial carbon and a ‘9th  sulfur’. Combining synthetic [Fe4S4] clusters with an assembly protein template, we show that sulfite gives rise to the ‘9th sulfur’ that is incorporated in the catalytically important belt region of the cofactor after the radical SAM-dependent carbide insertion and the concurrent 8Fe-core rearrangement have already taken place. This work provides a semi-synthetic tool for strategically labeling the cofactor—including its ‘9th  S’ in the belt region—for mechanistic investigations of nitrogenase while suggesting an interesting"
"link between nitrogen fixation and sulfite detoxification in diazotrophic organisms."

Location: 

Carol Lynch Lecture Hall

Chemistry Complex

Attached Document: 

Host: Dr. Tomson

inquiries rvargas@sas.upenn.edu

Inorganic Chemistry Seminar: Dr. Smaranda Marinescu, John Hopkins

Thu, 2018-09-13 12:00 - 13:00
Speaker: 
Dr. Smaranda Marinescu
Bio-Inspired Coordination Complexes and Polymers for Energy Applications

Research in the Marinescu group focuses on fundamental research to understand, design, and synthesize novel catalytic systems essential to the development of efficient solar-to-fuel technologies. Inspired by biological systems, we innovate molecular catalysts that involve hydrogen bonding networks capable of small molecule activation, and multiple proton and electron transfers. We have shown that cobalt complexes with pendant proton relays (NH groups) act as highly efficient catalysts for the reduction of CO2 to CO, and that the presence of the pendant NH moiety is crucial for catalysis.

 

 

 

We also explore the immobilization of metal complexes to electrodes as a method to combine homogeneous and heterogeneous catalysis. Metal-organic frameworks (MOFs) have emerged as a promising class of materials; however, the insulating nature of MOFs has limited their application as electrocatalysts. We have shown that metal dithiolene units can be successfully integrated into one- and two-dimensional (1D/2D) frameworks. The generated coordination polymers display unique electronic properties – they catalyze with remarkable activity the electrocatalytic conversion of water into hydrogen, and their electrical conductivity is among that of the best coordination polymers. We expect the design principles discovered in these studies to have a profound impact towards the development of advanced materials and sustainable technologies.

 

Location: 

Carol Lynch Lectrue Hall

Chemistry Complex

 Host: Dr. Schelter

inquiries rvargas@sas.upenn.edu

Physical Chemistry Seminar: Dr. Sean Roberts, University of Texas-Austin

Thu, 2018-12-13 13:00 - 14:00
Speaker: 

Dr. Sean Roberts

 

Manipulating Energy and Spin for Photon Up- and Down-conversion The negligible spin-orbit coupling in many organic molecules creates opportunities to alter the energy of excited electrons by manipulating their spin. In particular, molecules with a large exchange splitting have garnered interest due to their potential to undergo singlet fission (SF), a process where a molecule in a high-energy spin-singlet state shares its energy with a neighbor, placing both in a low-energy spin-triplet state. When incorporated into photovoltaic and photocatalytic systems, SF can offset losses from carrier thermalization, which account for ~50% of the energy dissipated by these technologies. Likewise, compounds that undergo SF’s inverse, triplet fusion (TF), can be paired with infrared absorbers to create structures that upconvert infrared into visible light. In this presentation, I will review our group’s efforts to create organic:inorganic structures that use SF and TF for improved light harvesting and photon upconversion.

Location: 

Carol Lynch Lectrue Hall

Chemistry Complex

Host: Dr. Anna

inquiries rvargas@sas.upenn.edu

Physical Chemistry Seminar: Dr. Wei Xiong, UC San Diego

Thu, 2018-11-01 13:00 - 14:00
Speaker: 

Dr. Wei Xiong

 

Ultrafast Nonlinear IR Spectroscopy for Exotic Molecular Materials


In this seminar, I will discuss two developments in ultrafast nonlinear IR spectroscopy for exotic molecular materials: (1) 2D IR spectroscopy for molecular vibrational polaritons and (2) transient electric field induced VSFG spectroscopy for probing interfacial charge transfer. Both show the advantages of ultrafast nonlinear IR spectroscopic technique: to decipher hidden physics of exotic molecular materials. 

2D IR of Molecular Polaritons.1 Molecular vibrational polaritons, half-light, half-matter hybrid quasiparticles, are studied using ultrafast, coherent 2D IR spectroscopy. Molecular vibrational-polaritons are anticipated to produce new opportunities in the photonic and molecular phenomena. Many of these developments hinge on fundamental understanding of physical properties of molecular vibrational polaritons. Using 2D IR spectroscopy to study vibrational-polaritons, we obtained results that challenge and advance both polariton and spectroscopy fields. These results invoke new developments in theory for the spectroscopy, discover observation of new nonlinear optical effects and unexpected responses from hidden dark states. We expect these results to have significant implications in novel infrared photonic devices, lasing, molecular quantum simulation, as well as new chemistry by tailoring potential energy landscapes. 

Transient E-field induced VSFG for Direct Interfacial Charge Transfer.2 We describe direct electron-transfer at buried interfaces between an organic polymer semiconductor film and a gold substrate, by observing the transient electric-field-induced vibrational sum frequency generation (VSFG).  We observe dynamic responses (<150 fs) where electrons are directly transferred from the Fermi level of gold to the LUMO of organic semiconductor. Transient spectra further reveal that, although the interfaces are prepared without deliberate alignment control, a sub-ensemble of surface molecules can adopt conformations for direct electron transfer, supported by DFT calculations. This result will have implications for implementing novel direct electron transfer in energy materials.

References.

1.        Xiang, B. et al. Two-dimensional infrared spectroscopy of vibrational polaritons. Proc. Natl. Acad. Sci. 115, 4845–4850 (2018).

2.        Xiang, B., Li, Y., Pham, C. H., Paesani, F. & Xiong, W. Ultrafast Direct Electron Transfer at Organic Semiconductor and Metal Interfaces. Sci. Adv. 3, e1701508 (2017). 

 

 

Location: 

Carol Lynch Lecture Hall 

Chemistry Complex

Host: Dr. Saven

inquiries rvargas@sas.upenn.edu

Physical Chemistry Seminar: Dr. Antoine Kahn, Princeton University

Thu, 2018-11-08 13:00 - 14:00
Speaker: 
Dr. Antoine Kahn
" Electron spectroscopy and the study of metal halide perovskite surfaces and interfaces"

 

 

  

 The formidable promises of the “re-discovered” class of organic/inorganic metal halide perovskites (MHP) such as methylamonium lead tri-iodide (MAPbI3), and the rapid and steady rise in device performance achieved with these materials over the past seven years, have triggered a flurry of research all over the world. This talk reviews our efforts to understand key surfaces and interfaces of these materials. We first report a combined ultra-violet/inverse photoemission spectroscopy (UPS/IPES) - DFT study of the surface electronic structure of several 3D-MHPs, e.g., MAPbI3, MAPbBr3, and CsPbBr3, which yield valence and conduction band edge positions (VBM, CBM), ionization energy and electron affinity (IE, EA), energy gap. An unusually low density of states is found at the VBM of these materials, with potential consequences on device physics. We then look at recent measurements of the electronic structure of MHP interfaces with hole and electron transport layers used for carrier extraction/blocking in photovoltaic devices. Specifically, the role of p-doping is investigated in the case of interfaces between the HTL poly(triarylamine) (PTAA) and CsPbBr3.  We then turn to two-dimensional metal halide perovskites (2D-MHP) and present electronic structure measurements on several 2D butylammonium methylammonium lead iodide and bromide compounds, BA2MAn-1PbnI3n+1, n=1 - 4. XRD, AFM, UV-vis absorption, and UPS/IPES spectroscopies are used to investigate these compounds.  Their single-particle gap is obtained from UPS/IPES results, and compared with optical absorption measurements to deduce an exciton binding energy (EB). In agreement with previous results, EB is found to be large for n=1 and 2 (390 and 110 meV, respectively), but drops rapidly for n=3 and above. Finally, a simple model is presented to justify the electron and hole levels and the single particle gap in these quantum wells structures.  

 

Location: 

Carol Lynch Lecture Hall

Chemistry Complex

Host: Dr. Rappe

inquiries rvargas@sas.upenn.edu

Department of Chemistry

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