Springer Theses Testing Molecular Wires: A Photophysical and Quantum Chemical Assay, (Paperback)

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 ?-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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 7.1.4. Femtosecond transient absorption spectroscopy . . . . . . . . . . . . . 80 7.1.5. Nanosecond laser Flash Photolysis . . . . . . . . . . . . . .