The Fundamental Dynamics and Optical Control of Molecular Devices

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With this award, the Chemical Structure, Dynamics and Mechanisms (CSDM-A) Program of the Division of Chemistry is funding Professor Sension of the University of Michigan, Ann Arbor to investigate molecular-based components of optically controlled nanomachines. These devices aim to provide a means for nanoscale remote-controlled sensing, transport, synthesis, memory, logic circuits, and information storage. The practical development of these devices faces significant challenges in design, arising from incomplete knowledge of the complicated systems involved. Professor Sension will use ultrafast spectroscopy to study the fundamental chemistry and physics of molecular processes relevant to molecular switches based on photochemical ring-opening reactions, molecular motors, based on isomerization around a central bond, and vitamin B12 analogues capable of photoactivated drug delivery. Methods will also be developed to use the wavelength, energy, phase, beam profile, polarization, and temporal structure of laser pulses intelligently to manipulate molecular constituents of potential devices. Students engaged in this research will receive training in modern experimental physical chemistry techniques, working on research problems relevant to biological processes, as well as nanotechnology and engineering. One of the most important reactions is the electrocyclic ring-opening reaction of substituted cyclohexadiene active in many molecular switches. Fundamental studies of small cyclohexadiene containing molecules will provide experimental data to inform theoretical efforts in a synergistic relationship. Study of the ring-opening reaction of 7-dehydrocholesterol is important as this is precisely the reaction that occurs in human skin to produce pre-vitamin D. The photoinitiated ring-opening reaction will be studied in liposomes, a physiologically relevant model system. This project also seeks to increase the fundamental understanding of cis-trans isomerization reactions key to molecular motors. The photochemical reactions of cobalamins are finding increased application in the sensors, antivitamins, and molecular drug-delivery devices. Fundamental studies of the ultrafast internal conversion and photodissociation of active cobalamins will be performed to understand the photochemistry and photophysics of these systems as a function of ligand, wavelength, temperature, and environment.