Seminars are usually held on Friday afternoon in room SL SL 130 at 3:15 pm, unless otherwise noted. Graduate student seminars are on Fridays in SL 130 or SL 110 at 3:15 pm, unless otherwise noted. Seminar speakers are available from 2:30 pm until 3:00 pm in CB275 for discussion. Refreshments are provided 15 minutes prior to the seminar in CB275.
The department strives to offer a diverse and vibrant seminar program. Each year leading researchers from outside the department, as well as faculty and graduate students from Western, present and discuss their cutting-edge research. This is an excellent opportunity for students, faculty, staff, and visitors to actively participate in the scientific community. In addition, many outside seminar speakers are recruiting graduate students for their respective programs and are eager to discuss their program. All are welcome and encouraged to attend!
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Winter Quarter 2019
Heptazine-based materials, including graphitic carbon nitride and poly(heptazine imides), are garnering increasing attention due, in part, to their improving photocatalytic hydrogen evolution activities (approaching 0.04 mol h-1 g-1, with apparent quantum yields of 60%). As such, there has been a recent focus on understanding the photochemistry of these materials. One major roadblock that has impeded those mechanistic studies is the chemically-ambiguous nature of the bulk carbon nitride active material. We have combined time-resolved photoluminescence (TR-PL) spectroscopy and computational chemistry to reveal upper excited-state dynamics that engender inter-molecular proton-coupled electron transfer (PCET) from water to a structurally-distinct small-molecule heptazine photocatalyst. To the best of our knowledge, this is the first direct spectroscopic evidence that the heptazine unit drives H-atom abstraction from water by PCET. This result yields rare spectroscopic evidence of an upper-excited state reaction pathway in a heptazine:H2O complex. This photoreaction exhibits a significant kinetic isotope effect (KIE) of 2.9, indicating homolytic O-H bond scission of water, and it liberates detectable hydroxyl radicals. Our results lay the groundwork for molecular design rules aimed at controlling organic photochemical reactivity by manipulating early-time photophysical dynamics. Photophysical and photochemical insight from our results can be leveraged in solar fuels research, photovoltaics, and LEDs.
In pursuit of an even more biologically active furanosteroid, we have also synthesized hibiscone B and its acetylated analog. Our syntheses, the first reported for both natural products, solve an important challenge to the synthesis of related members of the furanosesquiterpenoid family, namely the regio-, chemo-, and stereoselective reduction of one of two carbonyls in the diacylfuran subunit. These findings will be presented and their value discussed, particularly as it related to ongoing chemical biology efforts in our lab.
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