Title

From rotaxanes to molecular shuttles: Novel rotaxanes based on the inclusion complexation of phenyl and biphenyl guests by cyclobis(paraquat-P-phenylene) An experimental and theoretical study

Date of Award

1995

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

First Committee Member

Angel E. Kaifer, Committee Chair

Abstract

This dissertation presents the design, synthesis, and characterization of supramolecular assemblies such as rotaxanes and molecular shuttles. Rotaxanes are molecular assemblies composed of a cyclic bead which is threaded by a molecular wire and terminated by bulky stopper groups. Bead dissociation is prevented by the terminal groups. The preparation of rotaxanes is shown to involve the self-assembly of a macrocyclic electron-acceptor and an electron donor station. The presented methodology describes the preparation of rotaxanes containing two donor stations and only one bead, wherein the bead shuttles back and forth between the two stations at thermally controlled rates. This type of rotaxane is called a molecular shuttle. The use of two different donor stations leads to a molecular shuttle in which the average bead location can be controlled. The switching is shown to be controlled by both chemical and electrochemical stimuli. A novel rotaxane containing benzidine and biphenol donor stations has been prepared and shown to exhibit such switching properties.Computers can be a useful tool in understanding the structural and energetic consequences of molecular complexation between macrocyclic electron-acceptors and various electron-donating phenyl and biphenyl aromatic guests. In this study, the semiempirical molecular orbital method PM3 was used to optimize the geometries for a variety of inclusion complexes containing an aromatic guest and the cyclophane receptor, cyclobis(paraquat-p-phenylene), 2.1. Quantum mechanics is necessary in calculations of this type, since the binding contributions, most likely, consist of subtle electronic effects which could be overlooked by parameterized force-field calculations. Optimized geometries, heats of formation, and binding energies have been calculated, and compared to those found experimentally. In this thesis, the techniques of computational chemistry are used to verify experimental data, as well as to extend the current limits of experimentation to provide critical insight into the mechanism and action of molecular shuttles.

Keywords

Chemistry, Physical

Link to Full Text

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