Spin Dynamics of Photogenerated Multi-Spin Systems

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In this project, funded by the Chemical Structure, Dynamics & Mechanisms B Program of the Chemistry Division, Professor Michael R. Wasielewski of the Department of Chemistry at Northwestern University is developing new molecules with controllable spin transport properties. These molecules target new information processing strategies and take advantage of the quantum nature of electron spin. This work may lead to advanced computer technologies with broad applications throughout society. The use of organic materials and bio-inspired approaches to achieve this goal offers the possibility of developing new structures that are not only versatile, but are cost effective and environmentally benign as well. The group has an ongoing relationship with local middle and high schools through a partnership with the Office of STEM Education Partnership (OSEP) at Northwestern University. Working with OSEP, they are developing educational materials useful in teaching and for incorporating research into learning and education. Additionally, regular 1-2 day professional development workshops are held and week-long job shadowing experiences for teachers are implemented to provide a multiplier effect in connecting students to the rich learning resources at Northwestern University. Fast photo-initiated electron transfer within covalently-linked organic donor-acceptor molecules having specific donor-acceptor distances and orientations results in the formation of spin-correlated radical pairs (SCRPs) having well-defined initial spin configurations and magnetic interactions. Time-resolved electron paramagnetic resonance (EPR) and pulse-EPR spectroscopy are used to manipulate, control, and observe these coherent spin states. This new research investigates how spin sharing over multiple radical sites influences coherence dephasing in SCRPs; how electron transfer from a photo-excited stable radical to a distant site affects spin coherence; how coherent spin states can be propagated over long intramolecular distances using SCRPs; and how a photo-generated SCRP can produce transient spin frustration and propagate spin coherence within a three-fold symmetric molecular system. The project lies at the interface of organic, physical, and materials chemistry, and is therefore well suited to the education of scientists at all levels. This group is also well-positioned to provide the highest level of education and training for students underrepresented in science. Outreach activities involving K-12 students and their teachers are part of the project.