The field of molecular electronics and organic photovoltaics is steadily growing. One of the major themes in molecular electronics is the construction, measurement, and understanding of the current-voltage response of an electronic circuit, in which molecules may act as conducting elements. The investigated molecular structures in this thesis have been shown to be suitable for distance-independent charge transport. More precisely, the systems investigated were of particular interest due to their ability to provide efficient electronic coupling between electroactive units, and display wire-like behavior in terms of transferring charges from donors to acceptors. Besides impacting on the field of molecular electronics, the results of this research also has applications in the design and development of light harvesting, photoconversion and catalytic modules. This work is a great asset to the field of charge transport through organic pi-conjugated molecules.

I. Introduction and Motivation 1 1. Introduction to Molecular Electronics 2 1.1. Present Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.2. Limitations of Present Technology . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2. Motivation - Focusing on Molecular Wires 9 II. Theoretical Concepts 11 3. Concepts of Photoinduced Electron and Energy Transfer Processes Across Molecular Bridges 12 3.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 3.2. Electron TransferMechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 3.2.1. Superexchange . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 3.2.2. Charge Hopping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 3.2.3. Interplay ofMechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 3.3. Electronic Energy Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 3.3.1. Coulombic Energy Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . 26 3.3.2. Exchange Energy Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 4. Molecule-Assisted Transport of Charges and Energy Across Donor-Wire- Acceptor Junctions 30 4.1. Mechanisms of Charge Transfer throughMolecularWires . . . . . . . . . . . . 32 4.1.1. Superexchange Charge Transfer inMolecularWires . . . . . . . . . . . . 33 4.1.2. Sequential Charge Transfer inMolecularWires . . . . . . . . . . . . . . 34 4.2. Factors that Determine the Charge TransferMechanism . . . . . . . . . . . . . 36 4.2.1. Electronic Coupling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 4.2.2. EnergyMatching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 4.3. Specific Aspects of Photoinduced Electron Transfer in Organic Ï¿-conjugated Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 4.3.1. Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 4.3.2. The ClassicalMarcus Theory . . . . . . . . . . . . . . . . . . . . . . . . . 41 4.3.3. Photoexcitation and Relaxation Processes in Solution . . . . . . . . . . 45 4.3.3.1. Photoabsorption . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 4.3.3.2. The Franck Condon Principle and Radiative Transitions . . . . 49 4.3.3.3. The Franck Condon Principle and Radiationless Transitions . 52 4.3.3.4. Relaxation Processes Following Photoexcitation . . . . . . . . 55 4.3.3.5. Characterization by Stationary Spectroscopy . . . . . . . . . . 57 4.3.3.6. Characterization by Time-Resolved Spectroscopy . . . . . . . 58 4.3.3.7. Internal Conversion . . . . . . . . . . . . . . . . . . . . . . . . . 58 4.3.4. Influence of the Solvation on the Electronic Relaxation Dynamics . . . 59 4.3.4.1. Static Solvent Influence . . . . . . . . . . . . . . . . . . . . . . . 60 4.3.4.2. Dynamic Solvent Influence . . . . . . . . . . . . . . . . . . . . . 61 5. Examples of Molecular Wire Systems 63 5.1. Oligo(phenylenevinylene)s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 5.2. Oligophenylenes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 5.3. Oligo(thiophene) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 5.4. PhotonicWires . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 III.Results and Discussion 70 6. Objective 71 7. Instruments and Methods 79 7.1. Photophysics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 7.1.1. Absorption spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 7.1.2. Steady-state emission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 7.1.3. Time-resolved emission . . . . . . . . . . . . . . . . . . . . . . . ...

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