RUI: Host/Guest Interactions of Thermochromic and Photochromic Molecules in Binary Aqueous Media

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In this project, Prof. Maria T. Buthelezi and her students at Wheaton College receive support under the auspices of the Research in Undergraduate Institutions (RUI) activity from the Chemical Structure, Dynamics and Mechanism (CSDM) program of the Division of Chemistry to investigate the thermosolvatochromism and photochromism of spiropyran inclusion complexes with cyclodextrins and cyclophanes. In addition to the fundamental scientific appeal of studying this process, photochromic conversion of spiropyran (SP, closed ring form) to merocyanine (MC, open ring form) may be used in the development of on-and-off optical switching applications and materials for photochromic switches, photochromic lenses (optometry), fluorescent biomarkers, nanothermometers, and drug delivery devices. However, these photo- and thermal-interconversion processes are solvent dependent and thermally unstable, which have slowed the pace of application development using this system. In this project, systematic investigation of the impact of host compound structure and solvent composition on spiropyran/merocyanine interconversion will be investigated using steady-state optical spectroscopy, nanosecond time-resolved optical spectroscopy, calorimetry and computational methods. These studies are expected to identify combinations of host compound and solvent that stabilize the spiropyran/merocyanine system. Spiropyran is a photochromic and thermochromic molecule. Under visible light, spiropyran (SP) solutions are colorless, but when subjected to ultraviolet light, the solutions become colored as merocyanine (MC) is formed. When MC solutions absorb visible light, MC is converted back to SP molecule and the solution color disappears. This interconversion can be initiated with heat in some solvent mixtures. Conversions like this can be used in many important applications such as eyeglasses that adapt to varying light levels and optical digital storage devices. Utilizing this specific conversion in these kinds of applications requires a thorough understanding of how the solution components affect the conversion process. Prof. Buthelezi and her students will investigate this process under many conditions and using many methods in an effort to develop that understanding. The undergraduate students at Wheaton College will be involved in all aspects of this project and the hands-on experience gained from the proposed project will impact significantly their professional outlook and prepare them to pursue graduate or health professional studies and for eventual employment in academia, government laboratories, and industry.