Testing Molecular Wires (eBook)

Supervisor’s Foreword 7
Acknowledgments 9
Contents 11
Part I Introduction and Motivation 14
1 Introduction to Molecular Electronics 15
1.1…Present Technology 18
1.2…Limitations of Present Technology 18
References 20
2 Motivation---Focusing on Molecular Wires 21
References 22
Part II Theoretical Concepts 23
3 Concepts of Photoinduced Electron and Energy Transfer Processes Across Molecular Bridges 24
3.1…Introduction 24
3.2…Electron Transfer Mechanisms 25
3.2.1 Superexchange 27
3.2.2 Charge Hopping 30
3.2.3 Interplay of Mechanisms 32
3.3…Electronic Energy Transfer 32
3.3.1 Coulombic Energy Transfer 34
3.3.2 Exchange Energy Transfer 34
References 35
4 Molecule-Assisted Transport of Charges and Energy Across Donor--Wire--Acceptor Junctions 38
4.1…Mechanisms of Charge Transfer Through Molecular Wires 39
4.1.1 Superexchange Charge Transfer in Molecular Wires 40
4.1.2 Sequential Charge Transfer in Molecular Wires 41
4.2…Factors that Determine the Charge Transfer Mechanism 42
4.2.1 Electronic Coupling 42
4.2.1.1 Calculation of Electronic Coupling 42
4.2.2 Energy Matching 43
4.3…Specific Aspects of Photoinduced Electron Transfer in Organic pi -Conjugated Systems 45
4.3.1 Background 45
4.3.2 The Classical Marcus Theory 46
4.3.3 Photoexcitation and Relaxation Processes in Solution 49
4.3.3.1 Photoabsorption 49
4.3.3.2 The Franck--Condon Principle and Radiative Transitions 52
4.3.3.3 The Franck--Condon Principle and Radiationless Transitions 54
4.3.3.4 Relaxation Processes Following Photoexcitation 56
4.3.3.5 Characterization by Stationary Spectroscopy 58
4.3.3.6 Characterization by Time-Resolved Spectroscopy 58
4.3.3.7 Internal Conversion 59
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
References 62
5 Examples of Molecular Wire Systems 66
5.1…Oligo(phenylenevinylene)s 66
5.2…Oligophenylenes 68
5.3…Oligo(thiophene)s 69
5.4…Photonic Wires 70
References 71
Part III Results and Discussion 73
6 Objective 74
References 79
7 Instruments and Methods 80
7.1…Photophysics 80
7.1.1 Absorption Spectroscopy 80
7.1.2 Steady-state Emission 80
7.1.3 Time-resolved Emission 80
7.1.4 Femtosecond Transient Absorption Spectroscopy 81
7.1.5 Nanosecond Laser Flash Photolysis 82
7.2…Chemicals 82
7.3…Molecular Modeling 83
References 84
8 Energy Transfer Systems 85
8.1…Linking two C60 Electron Acceptors to a Molecular Wire 85
8.1.1 C60--oPPE--C60---A Representative Example for Efficient Energy Transfer 85
8.1.2 Energy Transfer in C60--oligo(fluorene)--C60 89
8.1.2.1 Molecular Modeling 89
8.1.2.2 Photophysics 93
8.2…Tunable Excited State Deactivation 98
8.2.1 Photophysics 100
References 106
9 Electron Transfer Systems 107
9.1…p-Phenyleneethynylene Molecular Wires 107
9.1.1 exTTF--oPPE--C60 Donor--Acceptor Conjugates 108
9.1.1.1 Electrochemistry 108
9.1.1.2 Photophysics 109
9.1.1.3 Molecular Modeling 117
9.1.1.4 Summary 124
9.1.2 H2P/ZnP--oPPE--C60 Donor--Acceptor Conjugates 124
9.1.2.1 Absorption Studies 127
9.1.2.2 Molecular Modeling 128
9.1.2.3 Photophysics 133
9.1.2.4 Summary 138
9.1.3 Meta-Connectivity---Influence of Structure on Molecular Wire Properties 139
9.1.3.1 Photophysics 142
9.1.3.2 Summary 150
9.2…oligo-Fluorene Molecular Wires 153
9.2.1 exTTF--oFL--C60 Donor--Acceptor Conjugates 154
9.2.1.1 Photophysics 154
9.2.1.2 Molecular Modeling 158
9.2.1.3 Summary 164
9.2.2 ZnP--oFL--C60 and Ferrocene--oFL--C60 Donor--Acceptor Conjugates 165
9.2.2.1 ZnP--oFLn--C60 165
9.2.2.2 Fc--oFLn--C60 172
9.2.2.3 Summary 176
References 179
10 Conclusions and Outlook 181
Curriculum Vitae 187
Publications 189
Conference Contributions 190