Topic: Vibronic couplings in solar energy coversion and environmental issues
Speaker: Associate Professor Rao Yi, Department of Chemistry and Biochemistry, Utah State University (USU)Date and time: May 23, 16:00–17:00Venue: Room 105, #5 Building of SPSTInteractions of electronic and vibrational degrees of freedom, namely vibronic couplings, are essential for understanding excited states relaxation pathways of molecular systems in bulk and at interfaces and surfaces. In this talk, I will give two examples of vibronic couplings applied to singlet fission and interfacial charge transfer.Part I: We examined the role of vibronic coupling in singlet fission using polarized transient absorption microscopy for solar energy conversion. It was found that singlet fission in pentacene is greatly facilitated by the vibrational coherence of a low frequency phonon, whose anisotropic coherence persists extensively for a few picoseconds. This coherence-preserving phonon that drives the anisotropic singlet-fission is made possible by a unique cross-axial charge transfer intermediate state. In the same fashion, this phonon was also found to predominantly drive the quantum decoherence of a correlated triplet pair to form a decoupled triplet dimer.Part II: I will present the development of interface-specific two-dimensional electronic-vibrational sum frequency spectroscopy (2D-EVSFG) for electronic-vibrational couplings for excited states at interfaces and surfaces for environmental issues. We demonstrate this 2D-EVSFG technique by investigating photoexcited interface-active molecules at the air/water interface as an example. Our 2D-EVSFG experiments show strong vibronic couplings of interfacial molecules upon photoexcitation and subsequent relaxation of a locally excited (LE) state. We believe that this development of 2D-EVSFG opens up a new avenue of understanding excited state dynamics related to interfaces and surfaces.Biography:
Dr. Rao is a physical chemist with expertise in interfacial science, ultrafast spectroscopy, and nonlinear optics. Rao has obtained his PhD in 2003 at the Institute of Chemistry, Chinese Academy of Science. In 2004, he joined Dr. Kenneth Eisenthal’s group at Columbia University as a postdoctoral fellow, in the area of experimental nonlinear interfacial spectroscopy. After his postdoc, Dr. Rao continued his career as a research associate, in collaboration with Drs. Nicholas Turro and Kenneth Eisenthal at Columbia University. Before his independent career, Dr. Rao worked as a research associate professor in the Department of Chemistry at Temple University in 2014. Dr. Rao joined the Department of Chemistry and Biochemistry at Utah State University as an assistant professor in 2017. His research interest is focused primarily on interfacial physical chemistry for environmental issues, solar energy conversion, and catalysis. In 2023, Dr. Rao was promoted to associate professor with tenure. Dr. Rao’s team has developed several state-of-the-arts interface-specific nonlinear optical spectroscopies for structures and dynamics at different interfaces. Dr. Rao is a recipient of National Science Foundation EARLY CAREER award, ACS Utah Outstanding Educator Award, Honda Research Institute Excellent Collaboration Award, and Research of the Year, College of Science, USU.
