Monitoring Structure-Function Relationships in Donor-Acceptor Systems for Electron Transfer.

摘要

The work in this thesis is aimed at gaining a better understanding of the structure-function relationships that exist in artificial electron transfer systems. The systems under investigation range from DNA to linear D-A systems to pi-stacking supramolecular assemblies. Each system was chosen to probe a specific structure-function relationship. The first series of molecules were made to examine the thermodynamic parameters of hole transport through DNA hairpins. The fixed distance between base pairs in DNA makes it an attractive scaffold for studying fundamental electron transfer events. In the second and third series of molecules, electron transfer originating from a strongly coupled charge transfer (CT) state in electron D-A1-A2 systems was examined. The second series focused on using julolidine as a donor because it has a modest oxidation potential and exhibits some conformational rigidity. Attachment of julolidine donor to naphthalene-1,8-dicarboximide (NMI) form a highly dipolar, low energy CT state, from which electron transfer was initiated to terminal electron acceptors. The third series focuses on increasing the structural rigidity of the donor by attaching perylene to NMI and examines the electron transfer dynamics to a secondary acceptor. The final two series focus on increasing the function of D-A1-A2 systems by forming pi-stacked solution-phase assemblies. In the first study, perylene-3,4;9,10-bis(dicarboximide) (PDI) is used to induce formation of solution-phase supramolecular assemblies. The redox potentials of PDI were tuned through bay region substitution, producing a molecule having both a green PDI as well as a standard red PDI. In the final study, PDIs were again used as terminal electron acceptors in a symmetric cruciform system. The cruciform design allows for greater control over the distance between the electron donor, a Zn-porphyrin, and the PDI, in which the two units are oriented 90° to one another. Electron transfer was demonstrated around this 90o bend, forming a long-lived ion pair state.