Electron Transfer through U-Shaped Donor-Bridge-Acceptor Molecules and Fluorescence Quenching of Conjugated Polyelectrolyte
Electron transfer reactions constitute a fundamental chemical process and are of intrinsic importance in biology, chemistry, and the emerging field of nanotechnology. Electron transfer reactions proceed generally in a few limiting regimes: nonadiabatic electron transfer, adiabatic electron transfer and solvent controlled electron transfer. Behavior between some of these regimes was examined by varying the solvents in which the reaction occurs i.e., the different polarization relaxation. In a 'fast' solvent, such as acetonitrile, the electron transfer occurs in the nonadiabatic regime over a broad temperature range; in a 'slow' solvent, such as N-methylacetamide (NMA) and N-methylpropionamide (NMP), the electron transfer reaction occurs in the nonadiabatic regime of high temperature but occurs in the solvent controlled regime as the temperature decreases. The semiclassical model was compared to the electron transfer rate data in the nonadiabatic regime and the Zusman model was compared to the rate constant in solvent controlled regime. Experimental data was discussed and compared to a theoretical interpretation between the regimes, â how the electron transfer mechanism converts from a nonadiabatic mechanism to a solvent controlled mechanism.
The fluorescence emission of conjugated polyelectrolytes is highly sensitive to their binding with other macromolecules, protein and dendrimers. A detailed investigation on the polyelectrolyte fluorescence intensity changes and the fluorescence quenching mechanism were explored. These studies confirm that the quenching mechanism is controlled by the electrostatic binding between the macromolecular analytes and the changes in the electronic characteristics of the polyelectrolyte. Three possible electrostatic mechanisms for the polyelectrolyte were explored: electron transfer, energy transfer, and internal conversion. In many cases, the conformational changes of the polyelectrolyte control the internal conversion, hence the fluorescence yield, when binding to other macromolecules, a qualitatively different mechanism from that found for small molecular analytes.
Advisor:Stephane Petoud; Kenneth D. Jordan; David H. Waldeck; Gilbert C. Walker
School:University of Pittsburgh
School Location:USA - Pennsylvania
Source Type:Master's Thesis
Date of Publication:03/20/2006