October 25, 2013 |
11 a.m.-12:30 p.m.
Nedderman Hall, Room 100 | Seminar Flyer
Dr. Valentine Vullev
Associate Professor, Departments of Bioengineering, Chemistry, and Biochemistry, and Materials Science and Engineering Program University of California, Riverside
Refreshments will be served at 10:45 a.m.
Understanding and utilizing dynamics at various time scales and system sizes represent an underlying theme for our research. Subpicosecond charge separation (at a molecular scale) and millisecond to second fluid dynamics (in microfluidic devices, at micrometer and millimeter scales) represent some of the extreme length and time scales that we investigate.
In relevance to solar energy conversion, the first part of the talk will focus on the kinetics of photoinduced charge transfer mediated by biomimetic and bioinspired systems. Our research focuses on the effects that local electric fields, generated by molecular dipoles, exert on electron and hole transduction. Such fields provide a means for accelerating charge separation (CS) and suppress the undesired charge recombination (CR). Therefore, we design bioinpsired electrets. (Electrets are the electrostatic analogues of magnets, i.e., they contain co-directionally ordered electric dipoles.) As expected, the electrets manifested rectification of photoinduced charge separation. That is, the rates of CS when electrons migrated toward the positive poles of the electret dipoles were considerably larger than the CS rates when the electrons moved in the opposite direction. Surprisingly, we observed similar effects for the CR processes, which disagreed with the theoretical predictions. Our experimental findings pointed out that conformation gating, induced by picosecond molecular dynamics, was an underlying reason for the observed CR trends. While molecular conformational gating is known to regulate kinetics in biochemical processes, it is overlooked in the design of organic electronic materials and devices. Understanding the coupling between local field effects and molecular dynamics, therefore, provides largely unexplored venues for energy science and molecular electronics.
The second part of the talk will cover our advances in single-molecule force-modulated kinetics. This methodology offers unique capabilities for direct observation of a range of structure-function relationships. For example, it is the only experimental approach that allows direct estimation of the displacements of the transition states during bimolecular interactions. Despite the conceptual simplicity of single-molecule force techniques, certain experimental design challenges have prevented such methodologies from becoming routinely used tools. Employing controlled surface chemistry has allowed us to address some of these issues. The presentation will conclude with the perspectives that these advances offer not only for basic-science research, but also for applied biomedical engineering.