Electron Transfer in Chemistry

Transcription

1 Vincenzo Balzani (Ed.) Electron Transfer in Chemistry 1 Principles and Theories Methods and Techniques WILEY-VCH Weinheim New York Chichester Brisbane Singapore Toronto

2 Contents Volume I Foreword Preface About the Editors List of Authors v ix lv lxvii Part 1 Principles and Theories 1 Piotr Piotrowiak (Ed.) 1 Electron Transfer: Theoretical Models and Computational Implementation 3 Marshall D. Newton 1.1 Introduction Kinetic Scheines Rate-Constant Models System Hamiltonian and Electronic States Diabatic Energy Surfaces TST Models Role of Solvent Dynamics Coupling Elements Basic Properties Comparison of Thermal and Optical Processes Pathway Analysis of T tf Applications of Theory Comparisons Based on Experimental Data Computational Studies 44

3 XIV Contents 1.6 Concluding Remarks 57 Acknowledgments 58 References 58 2 Adiabatic versus Non-Adiabatic Electron Transfer 64 Hitoshi Sumi 2.1 Adiabatic- versus Static-Coupling Scheme Non-Adiabatic Limit Single-Mode Model Atom-Tunneling Regime Semiclassical and Classical Regimes Multimode Model Adiabatic Limit Semiclassical Regime Attempt Frequency From the Adiabatic to the Non-Adiabatic Limit Adiabaticity Parameter Between the Adiabatic and the Non-Adiabatic Limit Further Development Large-Energy-Quantum Intramolecular Modes Electron Transfer to or from a Continuum of Free States Solvent-Fluctuation-Controlled Regime 97 Appendices 104 Appendix A: Direct Derivation of Equation Appendix B: Wigner Distribution Function 104 References Single- and Multi-electron Transfer Processes 109 Spiros S. Skourtis and David N. Beratan 3.1 Introduction Single-Electron Transfer Reactions Multi-Electron Transfer Reactions Conclusions 123 Acknowledgments 123 References Electron Transfer at Electrodes and Interfaces 126 Daniel Vanmaekelbergh 4.1 Scope Open Electron Systems The Electrochemical Potential Electronic Equilibrium between Two Phases Deviations from Equilibrium The Electronic Structure of Solids Free and Independent Electrons The Sommerfeld Model for Free Electrons in a Metallic Phase 134

4 Contents xv Occupation of the Electron-Energy Levels The Origin of Energy Bands Metals, Semiconductors and Insulators Extrinsic Semiconductors Electron-Energy Levels Corresponding to a Redox System The Electrochemical Potential of a Dissolved Redox System The Fluctuating-Energy-Level Model Proposed by Gerischer Interfacial Structure Metal Surfaces Physisorption and Chemisorption The Metal/Solution Interface The Semiconductor/Solution Interface Electron Tunneling The Probability of Electron Tunneling Interfacial Electron Tunneling Between Two Metals Experimental Tunneling Spectroscopy Electrochemical Reactions: Kinetics and Mechanism The Diversity of Electrochemical Processes Electrochemical Ion Transfer and Electrochemical Electron Transfer (ECIT and ECET) Current Density vs Overpotential: Experimental Results A Heuristic Treatment of Electrochemical Kinetics Electron Transfer between a Metal and a Simple Redox System Comparison between Electrochemical Electron Tunneling and Tunneling between Two Metals Current Density as a Function of Overpotential Marcus, Gerischer and the Phenomenological Rate Equations Comparison of Electron Transfer at a Semiconductor With Electron Transfer at a Metal Electrode 182 References Proton-Coupled Electron Transfer 189 Sharon Hammes-Schiffer 5.1 Introduction Continuum Theory for Single-Charge Transfer Single-Electron Transfer Single-Proton Transfer Multistate Continuum Theory for Proton-Coupled Electron Transfer Four-State Formulation Two-State Formulation Incorporation of Inner-Sphere Reorganization Extension to More than Two Charge-Transfer Reactions Applications of Proton-Coupled Electron Transfer in Solution Calculation of Input Quantities Proton-Coupled Electron Transfer through Asymmetrie Salt Bridges 209

5 XVI Contents 5.5 Fundamental Principles of Proton-Coupled Electron Transfer Future Directions 213 Acknowledgments 213 References Relationship between Electron and Electronic Excitation Transfer 215 Piotr Piotrowiak 6.1 Introduction Singlet Energy Transfer Triplet Energy Transfer Summary 232 Acknowledgments 233 References Charge-Transfer Excited States of Transition Metal Complexes 238 John F. Endicott 7.1 Defmitions and General Concepts Basic Concepts The Idealized Limit of Weak D/A Electronic Coupling (LWEC) Charge-Transfer Absorption Spectroscopy The Energies of Charge-Transfer Absorptions Charge-Transfer Excited-State Terms and Assignments The Analysis of Spectroscopic Absorption Bands Charge-Transfer Emission Spectroscopy The Interpretation of Charge-Transfer Emission Spectra The Classification of Charge-Transfer Absorption Bands The Electronic States Generated by Charge-Transfer Absorptions The Franck-Condon State in Transition Metal Complexes The Vibrationally Equilibrated Excited States (VEqES) Excited-State Relaxation Processes Vibrationally Equilibrated Excited States Relaxation Processes Upper-Excited-State Electronic-State Relaxation Observations on the Weak Electronic Coupling Limit: lon-pair Charge-Transfer Absorption Bands The Correlation of Observed lon-pair Charge-Transfer Energies with Experimental Electron-Transfer Parameters 252 Electronic Coupling in lon-pair Charge-Transfer Systems 253 lon-pair Charge-Transfer Absorption Band Widths 256 Ligand-to-Metal Charge-Transfer (LMCT) Absorption Bands 257 Energy Correlations for Simple Systems: M IIT (NH3) 5 (X~) Complexes 257 More Complex Ligand-to-Metal Charge-Transfer (LMCT) Systems. 259 Ligand-to-Metal Charge-Transfer (LMCT) Band Shapes and Intensities Metal-to-Ligand Charge-Transfer (MLCT) Absorption Band Energies 261

6 Contents xvn General Comments Metal-to-Ligand Charge-Transfer (MLCT) Excited-State Energies Band Shapes and Intensities Excited-State Lifetimes and Luminescence Properties Perspectives and Conclusions 266 Acknowledgements 267 References Synthetic Applications of Photocatalytic Oxidation and Reduction Reactions of Organic Reactants on Irradiated Semiconductor Surfaces 271 Marye Anne Fox 8.1 Introduction Principles Governing Photoelectrochemistry Redox Reactions on Irradiated Semiconductor Surfaces Comparison of a Photoelectrochemically Generated Electron-Hole Pair and a Moleculary Excited State Energy Considerations Solvent Effects Semiconductor Stability toward Catalytic Cycling Photosensitization Mechanism Chemical Selectivity through Photoelectrochemical Activation Adsorption and Surface Effects Potential Control Current Control Selective Photoelectrochemical Transformations Oxidations Reductions Cycloadditions and Retrocycloadditions Geometrie Isomerizations Miscellaneous Reactions Conclusions 305 Acknowledgments 306 References Radiative Charge Recombination and Electrochemiluminescence 312 Ann-Margret Andersson and Russell H. Schmehl 9.1 Introduction Processes Leading to Radiative Charge Recombination Annihilation of Anion and Cation Radicals Excimer and Exciplex Emission Reactions of Radical Ions with Other Reagents Chemically Induced Electron-Exchange Luminescence Kinetic Aspects Experimental Considerations: Techniques and Molecular Systems.. 323

7 xvni Contents Generation and Characterization of Reactive Species Molecular Systems Applications Sensors for Organic Substrates Employing [Ru(bpy)3] 2+ and Derivatives Sensors Employing Other ECL Chromophores Device Applications Summary 338 Acknowledgments 338 References Electron Transfer Reactions in Organic Chemistry 342 Stephen F. Neben 10.1 Introduction Inner- and Outer-Sphere Electron Transfer Reactions Bond Cleavage Reductive Cleavage of Single Bonds Heterolytic versus Homolytic Bond-Cleavage Reactions Rearrangements Initiated by Bond Cleavage in Radical Cations Additions to Single Bonds of Radical Cations Additions to n Systems of Radical Cations Trisubstituted Nitrogen Oxidations and Aminium Radical Cation Deprotonations Studies Focusing on Electron Transfer Kinetics of Organic Systems Intermolecular Reactions Intramolecular Reactions: Donor-Bridge-Acceptor Systems Intramolecular Reactions: Intervalence Compounds 379 References 386 Part 2 Methods and Techniques 393 Michael A. J. Rodgers (Ed.) 1 Classical Methods 395 Andreja Bakac 1.1 Introduction Mixing Methods Manual Mixing Rapid Mixing Relaxation Methods Temperature Jump Pressure Jump Spin-Relaxation Methods High-Pressure Techniques Indirect Methods and Special Cases 414

8 Contents xix Competition Kinetics Exchange Reactions 418 Acknowledgments 419 Abbreviations 419 References Electrochemical Techniques 422 Steen Uttrup Pedersen and Kim Daasbjerg 2.1 Electrochemical Techniques Introduction Heterogeneous Kinetics Mass Transport Homogeneous Kinetics Potential-Step Experiments Chronoamperometry Sampled-Current Voltammetry Double-Potential-Step Chronoamperometry Linear Sweep Voltammetry and Cyclic Voltammetry Charge-Transfer Reactions Nernstian Charge Transfer Quasi-Reversible and Irreversible Charge Transfer Ohmic Drop Coupled Chemical Reactions Mixed Charge Transfer and Kinetic Control Ultra-microelectrodes Fast-Transient Techniques Applications of UME in Resistive Media and under Industrial Conditions Steady-State Measurements at UMEs for Monitoring Slow Homogeneous Reactions Sensors Hydrodynamic Electrochemical Techniques Preparative Electrolysis Rotating Disc Electrode Combination of Electrochemistry and Spectroscopy Type Type Type Indirect Electrolysis 491 References Radiation-Chemlcal Techniques 503 George V. Buxton and Quinto G. Mulazzani 3.1 Introduction Interaction of Ionizing Radiation with Condensed Matter 504

9 XX Contents 3.3 The Radiation Chemistry of Water Properties of the Primary Radicals Generation of Secondary Radicals The Radiation Chemistry of Organic Liquids One-Electron Reduction and Oxidation in Nonaqueous Solvents Alcohols Acetone Acetonitrile Chlorinated Hydrocarbons Methyltetrahydrofuran and 2,2,4-Trimethylpentane Cyclohexane Dimethyl Sulfoxide Ammonia Solvent Mixtures Pulse Radiolysis Historical Perspective Pulse Radiolysis Facilities A Typical Modern Pulse Radiolysis Facility Other Methods of Detection Polarography Microwave Detection Magnetic Resonance Picosecond Pulse Radiolysis Data Capture and Analysis Purification of Materials and Preparation of Solutions Purification of Solvents Concluding Remarks 552 References 552 Further Reading Photochemical Techniques 558 Kevin Henbest and Michael A. J. Rodgers 4.1 Introduction The Significance of Photoexcitation for Electron Transfer Advantages of Photoexcitation The Methodology of Photokinetics Instrumentation Considerations Excitation Sources Detection and Measurement Techniques Optical Absorption Spectrometry Light-Scattering Spectrometry Fluorescence Instrumentation Frequency-Domain (Phase-Shift) Measurements Concluding Remarks 588 Acknowledgments 588 References 588