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DTSTART:20210314T100000
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DTSTART;TZID=America/Los_Angeles:20210225T120000
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DTSTAMP:20260618T193050
CREATED:20210120T172737Z
LAST-MODIFIED:20210120T172737Z
UID:13428-1614254400-1614254400@www.chemistry.ucla.edu
SUMMARY:Chem 218 Student Exit Seminar: Dane Stanfield
DESCRIPTION:A Tale of Two Doping Mechanisms: Controlling the Formation of Charge Transfer Complexes in Chemically Doped Semiconducting Polymers \nDoping of organic semiconductors has emerged as a viable route for the inexpensive fabrication of numerous electronic devices such as light emitting diodes\, thin film transistors\, and thermoelectric generators. The p-type doping of polymer based semiconductors like P3HT is achieved through the introduction of chemically strong oxidizing agents like F4TCNQ that usually undergo integer charge transfer\, removing an electron from the extended  conjugation network\, leaving behind a charged hole in its place that is free to conduct at the bulk level. In contrast\, p-type doping of small molecule based semiconductors typically results in formation of charge transfer complexes\, where close spatial contact and orbital overlap between the host and guest species cause fractional charge transfer to occur. It has to date remained unclear why polymeric based semiconductors show a preference for doping via integer charge transfer while their small molecule counterparts usually undergo formation of fractional charge transfer complexes. In this talk\, we will discuss recent advances in our understanding of the mechanisms that drive these two different types of charge transfer interactions in conjugated polymers. We show that it is possible to exert control over the type and abundance of each type of charge transfer interaction through the simple selection of processing solvent solubility parameters. We are also able to assign two structurally unique packing arrangements that correspond to integer or fractional charge transfer and compare the relative thermal stabilities of these two polymorphs. Finally\, we show that the CN groups found on the dopant molecule\, F4TCNQ\, can serve as a probe of the local electric field strength and thus the environment of the charge carriers as detected via the vibrational stark effect. Overall\, this improved understanding of polymer-dopant interactions allows us to provide new guidelines for enhancing the doping efficiency and limiting the occurrence of fractional charge transfer states in doped semiconducting polymers.
URL:https://www.chemistry.ucla.edu/seminars/chem-218-student-exit-seminar-dane-stanfield/
CATEGORIES:Other,Seminars
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DTSTART;TZID=America/Los_Angeles:20210225T160000
DTEND;TZID=America/Los_Angeles:20210225T160000
DTSTAMP:20260618T193050
CREATED:20210120T201235Z
LAST-MODIFIED:20210120T201235Z
UID:13437-1614268800-1614268800@www.chemistry.ucla.edu
SUMMARY:New Strategies for the Efficient Preparation of Bioactive Compounds
DESCRIPTION:Abstract: Novel technologies\, preparative methods and synthetic strategies often represent a critical part of the investigation of new design ideas for bioactive compounds. Traditionally\, natural products were considered to be the most challenging targets\, but frequently medicinal chemistry structure-activity relationship (SAR) studies are also limited in practice by synthetic tractability. This presentation will select two to three topics from currently ongoing projects in our group that have benefited from key contributions from technological\, methodological\, and strategic innovations. \nFor example\, we have recently reported the synthesis of iminothienopyridinediones through photooxygenation reactions. Our lead structure in this series was found to be a potent inhibitor of the oncogenic\, dual-specific phosphatase PTP4A3 (in vitro IC50 ~35 nM)\, as well as its family members PTP4A1 and PTP4A2. The SAR analysis as well as the scale-up of the iminothienopyridinedione chemotype were greatly facilitated by in-flow techniques\, first using fluoroelastomer tubing and a compact fluorescent lamp (CFL)\, and then a 3-D printed polypropylene cartridge system under LED light irradiation. \nAnother case study to be presented focuses on strategic innovations in the total synthesis and the investigation of the CNS/GPCR effects of Ergot Alkaloids. In particular\, the influence of scaffold rearrangement and stereochemistry on the serotonin (5-HT) receptor modulation of Ergot Alkaloid analogs will be highlighted\, a biological property that is significant for their potential for future development as anti-depression and anti-anxiety pharmaceuticals.
URL:https://www.chemistry.ucla.edu/seminars/new-strategies-efficient-preparation-bioactive-compounds/
CATEGORIES:Organic Colloquium,Seminars
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