Fundamental investigations of the self-assembly process of charged host and guest species for molecular electronics and light-harvesting applications.

摘要

In the field of supramolecular, or host-guest, chemistry, molecular components self-assemble into higher-ordered superstructures as a consequence of the mutually complementary recognition motifs that these species possess. The interactions responsible for the recognition are utilized in the template-directed syntheses of mechanically interlocked architectures, such as rotaxanes and catenanes, that would otherwise be difficult to obtain. The molecular toolbox utilized to construct these assemblies contains host and guest species that can be electron-rich and electron-poor, and typically one or more of the components possesses a formal charge and associated counterions. Accurately quantifying the interactions between hosts and guests is important for constructing highly-programmed molecular structures with desired properties. However, the role of the counterions in these systems is typically ignored for simplicity, even though counterions have the potential to contribute significantly to the thermodynamics and kinetics of host-guest associations. To ascertain the role of counterions in supramolecular systems, fundamental investigations were conducted and have yielded an improved method to quantify these interactions, as well as insights into the behavior of these complex mixtures. In a more applications-driven project, host-guest interactions have been employed to construct a noncovalent donor-chromophore-acceptor molecular triad for light-harvesting applications, which utilizes a charged electron-acceptor noncovalently bound to a crown ether cavity appended to the chromophore. Although this system was designed to harness light and convert it into useful energy, transient absorption spectroscopy studies suggested that limited, if any, electron transfer took place. In addition, the molecular toolbox utilized to construct host-guest systems was expanded to include a new class of all-aromatic, charged macrocycle hosts. These macrocycles were found to complex a neutral guest species, tolerate a wide range of chemical conditions, and have potential use in molecular electronics applications.