The Chemical Structure, Dynamics and Mechanisms Program supports Professor Martin Kirk at the University of New Mexico who will use a combined spectroscopic, magnetic, and computational approach to understand the electronic structure of new donor-acceptor (D-A) biradicals and (py)2M(dioxolene-A)2 (dioxolene = semiquinone/catecholate) extended arrays that possess organic mixed-valency. The proposed D-A systems are ground state analogues of charge separated states generated in photoinduced electron transfer processes, and therefore have direct relevance to various magnetic electron transport conduits, including molecular rectifiers and spintronic devices. The overarching focus of this work is the use of D-A biradicals to facilitate strong D-A electronic coupling and ferromagnetic exchange interactions over great distances. The proposal represents a concise research plan directed toward the achievement of broader long-range goals of adding to the molecular electron transport knowledge base. This will occur through the development of a complete electronic structure description of strong electronic coupling in D-B-A biradicals and through understanding the origin of long-range ferromagnetic exchange mediated by delocalized electrons.
With the support of the Chemical Structure, Dynamics and Mechanisms Program in the Chemistry Division at the National Science Foundation, Dr. Martin Kirk is performing research in an area of enormous interest. Phenomena such as long-range charge and energy transport in organic and metallo-organic systems are relevant to solar-energy conversion, electronics, and information processing. This work will contribute to the design of new multifunctional supramolecular systems that may function as vital components in magnetic, conducting, electroactive, photoactive, and spintronic devices. Broader impacts will involve teaching, training and learning through collaborative interactions with undergraduate programs at New Mexico Tech and San Jose State University. The diverse culture at the University of New Mexico, with approximately 50% underrepresented persons, has allowed Professor Kirk's group to be represented by students of African, African American, Pacific Island, Chinese, European, and Indian heritage. Approximately half of these have been women and some have been supported through NM-AGEP, an NSF program aimed at increasing the number of minority Ph.D.'s in science and technology.
Nature of the Project: Experimental studies of magnetic electron donor-acceptor interactions allow us to obtain vital information regarding how molecules can function as key components of molecular electronic devices in order to facilitate fast electron transport, directional electron transport, and spin-polarized electron transport. Organic molecules are beginning to play important roles in the development of spin-transport materials since they possess specific advantages over their metal-based counterparts. Also, the use of organic and metallo-organic systems may allow for specific advantages over traditional solid-state spintronic (spin electronic) materials since they can be synthetically manipulated with ease and incorporated into hybrid materials. This aspect of flexibility may lead to highly tunable magnetic, photonic, and electron transport properties. Our work has shown that long-range magnetic interactions between localized electron spins can be efficient in molecular systems. Developing electronic structure descriptions of donor-acceptor electronic coupling in magnetic donor-bridge-acceptor (D-B-A; B = bridge molecule) systems, understanding the electronic origin of long-range electron spin coupling, and their respective relationships to molecular electronic devices and materials have formed the basis of our work. Our laboratories are a student training ground for these studies, and the undergraduate, graduate, and postdoctoral researchers trained under this award will contribute to the vitality of US efforts in generating next-generation technologies and developing the workforce to enable them. Outcomes and Findings: Intellectual Merit The final outcomes and findings of the project have already been, or will be, broadly disseminated in the scientific literature and at a variety of scientific meetings and conferences. Here, we present a summary of key outcomes and findings resulting from the funded project. Our work on the electronic structure and spectroscopy D-B-A biradical molecules has allowed us to understand the electronic origin of ground state spin alignment (i.e. ferromagnetic exchange coupling) in these molecule-bridged biradicals that possess two unpaired electron spins. Our work has allowed us to quantify the magnitude of the bridge mediated electronic coupling in these molecules as a function of both D-A distance and mode of D-A connectivity with the bridge molecule. The spectroscopic evaluation of excited state contributions to large electronic couplings is important to advancing our understanding of how molecules facilitate the transfer or transport of electrons, particularly with respect to how single molecules may mediate efficient and directional electron transport and even spin-polarized electron transport in spintronic devices. With respect to the spin-polarized electron transport problem, our work has shown how localized organic radicals can be ferromagnetically exchange coupled over nanoscale distances. Broader Impacts Our work has contributed to a better understanding of design principles that will enable molecular electron transport in functional devices. This could impact new technologies that exploit magnetic molecules in molecular electronis and solar energy devices. Our work contributes to a better understanding of molecule-assisted electron transport at the nanoscale. Our work on strong interactions between delocalized electron spins and localized electron spins impacts our ability to understand the exchange interaction between delocalized electrons and magnetic impurities in technologically important dilute magnetic semiconductor materials. Our work on D-A interactions in delocalized organic molecules could find applications as spin-polarized electron injectors, molecular wires, and molecular rectifiers that function on the nanoscale. The University of New Mexico is a majority-minority institution. Our undergraduate chemistry program has a high percentage of minority and other traditionally under-represented groups, and both undergraduate and high-school students have benefitted from our research program. We feel that our students should have a hands-on experience with state of the art instrumentation since chemistry is an experimental science. It is through experimentation that new knowledge is generated, and it is through experimentation that students are challenged and the learning process is solidified. As a result, we encourage high school students and undergraduates to participate in our research program. Our research program also includes the participation of graduate and postdoctoral researchers who have attended state, national, and international meetings, and presented talks, posters, and papers detailing our research endeavors.
