Title

Self-assembly of dendrimers and highly coupled ferrocene dimers via hydrogen bonding

Date of Award

2006

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Chemistry

First Committee Member

Angel E. Kaifer, Committee Chair

Abstract

This dissertation investigates the application of multiple hydrogen-bonding in supramolecular chemistry in two important aspects: to self-assemble Newkome-type dendrimers and to assistant electronic communication between ferrocene redox centers. Additionally, the author describes a simple analytical method for the determination of the number of electrons in faradaic processes. These studies were performed by a broad range of techniques including, 1D-NMR, 2D-NMR, PGSE-NMR spectroscopy, mass spectroscopy, vapor pressure osmometry, cyclic voltammetry, UV-visible spectroscopy, steady-state fluorescence spectroscopy, and X-ray diffraction.Chapter one is a brief introduction of the application of hydrogen-bonding in supramolecular chemistry. The specific reversibility and directionality make multiple hydrogen bonding stand out among other covalent and noncovalent interactions to assemble well-defined supramolecular structures. This is not surprising since nature employs hydrogen bonding in a wide range of processes.Chapter two describes the preparation and physical characterization of a new series of unsymmetric Newkome-type dendrimers. These dendrimers contain a single ureidopyrimidine residue covalently attached to their apical positions. In low polarity solvents, the first and second generation dendrimers form highly stable dimers via hydrogen bonding of their DDAA ureidopyrimidine units, while the third generation dendrimer dimerizes to a very low extent. Additionally, solvent play an important role in equilibrium between tautomers, and pi-stacking interactions are found between aromatic solvent molecules like toluene, and the "aromatic ring" in the dimers.Chapter three describes the synthesis, electrochemical and photochemical characterization of a novel ferrocene derivative containing a hydrogen bonding motif in its DDAA pyrimidinedione unit. It forms highly stable, noncovalent dimers in chloroform and dichloromethane solutions. Its voltammetric behavior and the observation of an intervalence charge-transfer band and the fluorescence quenching on a pyrene fluorophore reveal the strong electronic coupling between ferrocene centers in the hydrogen-bonded dimer.Chapter four describes a new, convenient method to determine the number of electrons (n) involved in a faradaic process, using a series of four compounds containing two, three, four and eight equivalent ferrocene centers. The method takes advantage of pulse gradient stimulated echo (PGSE) NMR spectroscopy to determine the diffusion coefficient of the electroactive species. The value of n is subsequently determined from the steady-state limiting current (iL) measured on a disk ultramicroelectrode.

Keywords

Chemistry, Organic; Chemistry, Physical

Link to Full Text

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