Undergraduate Thesis Or Project
 

Photodimerization of Organic Semiconductors in the Strong Coupling Regime

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  • Organic semiconducting materials have emerged in the last few decades as viable alternatives to inorganics in broad applications from field effect transistors to LEDs to solar cells. Organics provide many benefits over inorganics such as flexibility, sustainability, and reduced cost. However, these materials are more susceptible to degradation in the presence of light and oxygen, which prevents them from fully replacing silicon in electronics. Recently, techniques from polariton chemistry have been utilized in condensed matter physics research to tune material properties, such as chemical reaction rates, using interactions between light and matter. Light-matter interactions have been shown to reduce rates of oxidation in two organic semiconductors, P3HT and TDBC. This thesis explores the effects of strong light-matter interactions on photo-chemical reactions in acene-based semiconductors. The photodegradation of soluble derivatives of pentacene and tetracene, two benchmark organic semiconducting materials capable of singlet exciton fission, are explored under the influence of strong light-matter coupling in optical microcavities. The dominant degradation process in cavities is determined to be photon-induced dimerization, a process possible even in anaerobic conditions. Despite well over a century of research into the dimerization of acene-based molecules, a novel photodimerization reaction in 5,12-Bis((triisopropylsilyl) ethynyl) tetracene films is reported, resulting in an alkyne dimer as opposed to the butterfly dimer that, in tetracene, had been observed exclusively prior to this report. Optical properties and chemical structure of this new dimer species are presented. Rates of both alkyne photodimerization in tetracene films and photodimerization in pentacene films are found to increase under the influence of strong coupling. The ability to enhance chemical reaction rates in organic semiconductors, which often proceed through charge or energy transfer, with optical microcavities may enable enhanced photogeneration efficiency in solar cells, which proceeds through similar processes. Better understanding polaritonics in singlet fission materials could also allow for benefits in the efficiency of solar cells and photodetectors. Furthermore, investigating chemical reactions of acene-based molecules in the strong coupling regime yields new insights into how polariton states interact with molecular states. Techniques presented can be utilized to probe the effects of light-matter coupling on the dynamics of various exciton reservoirs, which could have broad applications in future research of these and other materials.
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  • Ostroverkhova group website
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  • Funded by the National Science Foundation (NSF CHE-1956431)
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