Oligoethylene Glycol Solubilized Crankshaft Lactone Molecular Switches Eva
Oligoethylene Glycol Solubilized Crankshaft Lactone Molecular Switches Eva Charlesworth-Seiler, Yunuen Torres, and Bart Dahl Department of Chemistry University of Wisconsin-Eau Claire, WI 54702 Molecular Switches: Previous Work: Tertbutyl Substituted Molecular Switches Molecules that can reversibly convert between two forms exhibiting different properties. Interconversion between states does not happen spontaneously, but in response to certain stimuli. Geometry and Conjugation: The physical properties, including spectroscopic and electronic properties, of compounds containing aryl-aryl bonds are highly dependent on the torsional angle between the arene subunits. Co-planar configurations of oligoarene-containing compounds favor a higher degree of conjugation which has been shown to manifest itself as more efficient electronic conductance as well as absorption and emission of light. Simple unsubstituted biphenyl and oligophenyl-containing compounds have non-planar configurations at energetic minima. Additionally these simple systems are not capable of input-driven torsional angle switching and therefore are not candidates for molecular switches. However, analogous compounds containing reversibly cleavable bridges across the individual arene units could provide this feature. This has led to much recent interest in developing bridgedbiphenyls with aryl-aryl geometry switching capabilities. Because the properties of biphenyls and oligophenyls are so highly dependent on torsional angle, compounds capable of reversible geometry switching should also have switchable electronic and spectroscopic properties. This could ultimately lead to technological applications in important areas such as organic electronics, including light emitting diodes and field effect transistors, as well as molecular machines and switches, tunable fluorescent dyes, and sensors. Switching Studies: p. H Stimulus Molar Absorptivity Compounds 7, 12, and 18 correspond to the ring opened non-planar state of 1, 2, and 3 respectively. Current Work: Oligoether Substituted Terphenyls Three oligoether substituted moieties have been synthesized in small quantities. We are working to make more of the most promising candidate and optimize the synthesis. Oligoethers sufficed in prevention of pi stacking to afford organic soluble terphenyl switches. UV Fluorescence Compounds 1, 2, and three respond to base stimulus by switching off their enhanced spectroscopic properties. Addition of acid effectively switches them back to the highly conjugated planar conformation. Fluorescence Emission All three crankshaft compounds have much higher quantum yields compared to their precursors. Increasing the conjugation length also increases quantum yield. Acknowledgments • Wisc. AMP-Wisconsin Alliance for Minority Participation • University of Wisconsin-Eau Claire Chemistry Department • University of Wisconsin-Eau Claire Office of Research and Sponsored Programs • American Chemical Society Petroleum Research Fund • Learning and Technology Services at UWEC • Research Corporation for Scientific Advancement 1 H NMR Spectra Breaking the lactone tethers of the terphenyl molecular switch results in upfield shift of 1 H NMR peak positions. References Dressler, Justin J. ; Miller, Sarah, A. ; Meeuwsen, Brian T. ; Riel, Asia Marie S. ; Dahl, Bart J. “Synthesis of Dilactone Bridged Terphenyls with Crankshaft Architectures. ” Tetrahedron 2015, 71, 283 -292. Carlson, Erik J. ; Riel, Asia Marie S. ; Dahl, Bart J. “Donor. Acceptor Biaryl Lactones: p. H Induced Molecular Switches with Intramolecular Charge Transfer Modulation. ” Tetrahedron Lett. 2012, 53, 6245 -6249
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