Date of Award
Open Access Dissertation
Chemistry and Biochemistry
Linda S Shimizu
From the formation of rock candy crystals, to the functionality of DNA in the cell, to the cosmic dust throughout the universe, supramolecular chemistry has a great impact and importance in the world around us. In this thesis, we explore the supramolecular interactions and self-assembly of bis¬-urea macrocyclic systems and investigate how their structure and assembly influences bulk properties and functionality. Specifically, in chapter one, we review the factors that guide, limit, and define supramolecular structures from the atomic to the centimeter scale.
In chapter two, we investigate the incorporation of benzophenone, a well known triplet sensitizer, within a bis-urea macrocycle and its effects on the photophysical properties. Bis-urea macrocycles consist of two urea groups and two C-shaped spacers. We observe upon self-assembly that the benzophenone bis-urea macrocycle generates a host with an unusually stable radical, which was detected by Electron Paramagnetic Resonance spectroscopy (EPR). The host crystals are porous structures that are able to absorb guests including alkenes and aromatics in the interior channel. UV-irradiation of the benzophenone macrocycle in oxygenated solvents resulted in the generation of singlet oxygen. Solid complexes of the host and 2-methyl-2-butene or cumene facilitated selective oxidation of the guest in good conversion when irradiated under an oxygen atmosphere.
In chapter three, we investigate the synthesis and assembly of macrocyclic systems that employ expanded aryl spacers. Incorporation of 2,7-dimethyl naphthalene resulted in a macrocycle that had a unique "bowl shaped monomer with an unusual parallel urea conformation that disrupted the typical urea self-assembly. The incorporation of 1,3-dimethyl and 4-bromo-1,3-dimethyl naphthalene spacers showed the formation of macrocycles that display favorable conformations for the assembly into columnar structures. The bromo analog shows a propensity for halogen bonding interactions.
Finally, in chapter four, we explore the co-crystallization of a pyridyl bis-urea macrocycle with halogenated compounds in order to examine the ability of this macrocycle to act as a Lewis base in the formation of halogen bonds. The macrocycle was co-crystallized with a series of halogen bond donors. X-ray quality crystals were obtained by slow evaporation of the host with iodopentafluoro benzene and diiodotetrafluoro ethane from methylene chloride solutions. The crystal structures of these complexes show very strong halogen bonds with R-X***B distances from 2.179- 2.745 Å that are of an average only 78 % of the sum of the Van der Waals radii for iodine and oxygen. These halogen bonds were also analyzed through DFT calculations, and we estimate the association energies to be 7.381 kcal mol-1 for iodopentafluoro benzene and 10.331 kcal mol-1 for diodotetrafluoro ethane. These results suggest that the pyridyl hosts will be a strong organizing motif for co-crystallizing electrophilic halides. In the future, we plan to explore the application of this motif for organizing molecules with important optical and electronic properties.
Geer, M. F.(2013). The Scope of the Bis-Urea Macrocycle Assembly Motif. (Doctoral dissertation). Retrieved from http://scholarcommons.sc.edu/etd/2390