Rapid Reactions of Ions and Radicals in Organized and Constrained Media: Polymer Films and Zeolites

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Supported by the Organic Dynamics Program, Professor Kerry Thomas of the University of Notre Dame studies rapid reactions of ions and radicals in organized and constrained media. Low-energy photochemical and high-energy radiolytic reactions of organic probe molecules held within zeolites and solid polymers permit assay of the rates of development of spectra of the resulting ions, allowing the exploration of the effects of host modification on the unique ion kinetics occurring in these systems. Small pools of organic solvents are created within the cavities of zeolites, constraining and stabilizing usually short-lived charge-separated ionic species which would otherwise be rapidly neutralized. Migration of energy and charge to probe molecules held within solid polymeric hosts is induced by excitation of the polymer. Both the zeolite and the polymer systems share a common feature, the rapid migration of energy deposited in one region to a selected region, creating chemistry at the targeted site. Fundamental questions of energy conversion, transport, and loss are at the heart of many important technological processes. Through an examination of the reactions with light and with high-energy electrons of organic molecules constrained to remain within a tightly-defined `cage` rather than freely moving in solution, Professor Thomas explores the mechanisms of formation and reaction of free electrons, organic radicals (compounds containing an odd number of electrons), and organic ions (compounds bearing either positive or negative charges). Ongoing studies target the role of the `host` both in the generation of these reactive species through the transfer of energy from the host to the organic molecules contained within it and in the moderation of the transport and reactivity of these reactive species. These studies shed light on energetic excitation processes such as those employed in x-ray photolithography, wherein high-resolution structures of use, for example, in microelectronic circuitry production, are produced through the radiation-induced formation or destruction of polymeric materials