Photochemistry and Photophysics

Vincenzo Balzani is Emeritus Professor of Chemistry at the University of Bologna, Italy. His scientific activity is documented by eight books and ~650 scientific papers in the fields of photochemistry, supramolecular chemistry, molecular machines, and solar energy conversion. Paola Ceroni is Professor at the University of Bologna. She has published ~250 scientific papers. Alberto Juris is former Associate Professor of General and Inorganic Chemistry at the University of Bologna.

• From the Preface to the First Edition xviiPreface to the Second Edition xixAcknowledgments xxvList of Abbreviations xxvii1 Introduction 11.1 Photochemistry and Photophysics in Science and Technology 11.2 Historical Notes 21.3 A New Dimension of Chemistry and Physics 31.4 The Nature of Light 51.5 Absorption of Light 71.6 Quantum Yield, Efficiencies, and Excited-State Reactivity 8References 102 Elementary Molecular Orbital Theory 112.1 Introduction 112.2 The Hydrogen Atom 112.3 Polyelectronic Atoms 132.4 From Atoms to Molecules 182.5 Electronic Structure of Homonuclear Diatomic Molecules 222.6 Electronic Structure of Heteronuclear Diatomic Molecules 262.7 Simple Polyatomic Molecules and Elements of Group Theory 272.7.1 Elements of Group Theory 272.7.2 Water 312.7.3 Ammonia 322.8 Typical Organic Molecules 342.8.1 Methane 342.8.2 Ethene 352.8.3 Benzene 382.8.4 Formaldehyde 402.9 Transition Metal Complexes 422.9.1 General Concepts 422.9.2 Typical Metal Complexes 49References 533 Light Absorption and Excited-State Deactivation 553.1 Light Absorption 553.1.1 Selection Rules 573.1.2 Symmetry Selection Rules 573.1.3 Spin Selection Rules 593.1.4 The Franck–Condon Principle 593.1.5 Visualization of Photochemical Reactions on Potential Energy Surfaces 623.2 Jablonski Diagram 643.3 Excited-State Deactivation 673.3.1 Vibrational Relaxation 673.3.2 Radiationless Deactivation 673.3.3 Radiative Deactivation 733.3.4 Radiative Lifetime 743.4 Chemical Reactions 753.5 Kinetic Aspects 753.6 Solvent and Temperature Effects 773.6.1 Solvatochromic Shift 773.6.2 Crossing of States 813.6.3 Temperature Effects on Excited-State Lifetime 813.6.4 Thermally Activated Delayed Fluorescence 823.7 Selected Species 833.8 Semiconductors 99References 1034 Excited States: Physical and Chemical Properties 1094.1 Excited State as a New Molecule 1094.2 Lifetime 1094.3 Energy 1104.4 Geometry 1114.4.1 Small Molecules 1124.4.2 Ethene 1144.4.3 Ethyne 1144.4.4 Benzene 1154.4.5 Formaldehyde 1164.4.6 Square Planar Metal Complexes 1164.5 Dipole Moments 1174.6 Electron Transfer 1194.7 Proton Transfer 1224.8 Excimers and Exciplexes 125References 1275 From Molecules to Supramolecular Systems 1295.1 Supramolecular (Multicomponent) Systems and Large Molecules 1295.2 Electronic Interaction in Mixed-Valence Compounds 1315.3 Electronic Interaction in Donor–Acceptor Complexes 1335.4 Electronic Stimulation and Electronic Interaction in the Excited State 1355.5 Excimers and Exciplexes Formation in Supramolecular Systems 138References 1406 Quenching and Sensitization Processes in Molecular and Supramolecular Species 1436.1 Introduction 1436.2 Bimolecular Quenching 1446.2.1 Stern–Volmer Equation 1446.2.2 Kinetic Details 1466.2.3 Static vs Dynamic Quenching 1476.2.4 Sensitized Emission Quantum Yield 1486.2.5 Spin Considerations 1496.3 Quenching and Sensitization Processes in Supramolecular Systems 1506.4 Electron-Transfer Kinetics 1536.4.1 Marcus Theory 1546.4.2 Quantum Mechanical Theory 1576.4.2.1 The Electronic Factor 1586.4.2.2 The Nuclear Factor 1606.4.2.3 Optical Electron Transfer 1606.5 Energy Transfer 1616.5.1 Coulombic Mechanism 1636.5.2 Exchange Mechanism 1656.6 Role of the Bridge 1666.7 Catalyzed Deactivation 168References 1687 Molecular Organic Photochemistry 1737.1 Introduction 1737.2 Alkenes and Related Compounds 1737.2.1 Basic Concepts 1737.2.2 Photoisomerization of Double Bonds 1747.2.3 Electrocyclic Processes 1767.2.4 Sigmatropic Rearrangements 1777.2.5 Di-π-Methane Reaction 1787.2.6 Photocycloaddition Reactions 1787.2.7 Photoinduced Nucleophile, Proton, and Electron Addition 1797.3 Aromatic Compounds 1807.3.1 Introduction 1807.3.2 Photosubstitution 1807.3.3 Photorearrangement 1827.3.4 Phototransposition 1827.3.5 Photocycloadditions 1827.4 Carbonyl Compounds 1867.4.1 Introduction 1867.4.2 Photochemical Primary Processes 1877.5 Photochemistry of Other Organic Compounds 1887.5.1 Nitrogen Compounds 1887.5.1.1 Overview 1887.5.1.2 Photoisomerization of Azocompounds 1897.5.2 Saturated Oxygen and Sulfur Compounds 1897.5.3 Halogen Compounds 190References 1948 Photochemistry and Photophysics of Metal Complexes 1978.1 Metal Complexes 1978.2 Photophysical Properties: General Concepts 1978.3 Photochemical Reactivity: General Concepts 1988.4 Relationships Between Electrochemistry and Excited-State Properties 2008.4.1 Cobalt Complexes 2008.4.2 Copper Complexes 2018.4.3 Ruthenium Polypyridine Complexes 2028.4.4 Excited-State Redox Potentials 2048.5 Luminescent Metal Complexes 2068.5.1 Ruthenium Complexes 2078.5.2 Rhodium Complexes 2088.5.3 Iridium Complexes 2108.5.4 Platinum Complexes 2128.5.5 Chromium Complexes 2178.5.6 Iron Complexes 2228.5.7 Copper Complexes 2268.5.8 Lanthanoid Complexes 2288.5.9 Porphyrin Complexes 2318.6 Photochemical Processes 2358.6.1 Types of Photoreactions 2358.6.1.1 Photodissociation and Related Reactions 2358.6.1.2 Photooxidation–Reduction Reactions 2368.6.1.3 Intramolecular Rearrangements 236References 2379 Experimental Techniques 2459.1 Apparatus 2459.1.1 Light Sources 2459.1.2 Monochromators, Filters, and Solvents 2529.1.3 Cells and Irradiation Equipment 2549.1.4 Detectors 2569.2 Steady-State Absorption and Emission Spectroscopy 2589.2.1 Absorption Spectroscopy 2589.2.1.1 Instrumentation 2599.2.1.2 Qualitative and Quantitative Applications 2609.2.1.3 Sample Measurement 2609.2.2 Emission Spectroscopy 2619.2.2.1 Instrumentation 2619.2.2.2 Emission Spectra 2639.2.2.3 Excitation Spectra 2639.2.2.4 Presence of Spurious Bands 2649.2.2.5 Quantitative Relationship Between Luminescence Intensity and Concentration 2669.2.2.6 Stern–Volmer Luminescence Quenching 2679.2.2.7 Emission Quantum Yields 2689.3 Time-Resolved Absorption and Emission Spectroscopy 2719.3.1 Transient Absorption Spectroscopy 2719.3.1.1 Transient Absorption with Nanosecond Resolution 2719.3.1.2 Transient Absorption with Femtosecond Resolution 2739.3.2 Emission Lifetime Measurements 2749.3.2.1 Single Flash 2749.3.2.2 Gated Sampling 2759.3.2.3 Upconversion Techniques 2769.3.2.4 Single-Photon Counting 2769.3.2.5 Data Analysis 2789.3.2.6 Phase Shift 2799.3.2.7 Luminescence Lifetime Standards 2819.4 Absorption and Emission Measurements with Polarized Light 2819.4.1 Linear Dichroism 2819.4.2 Luminescence Anisotropy 2839.4.3 Circular Dichroism 2849.4.4 Circularly Polarized Luminescence 2859.5 Reaction Quantum Yields and Actinometry 2879.5.1 Reaction Quantum Yields 2879.5.2 Actinometry 2889.5.2.1 Potassium Ferrioxalate 2899.5.2.2 Potassium Reineckate 2909.5.2.3 Azobenzene 2919.6 Other Techniques 2929.6.1 Photothermal Methods 2929.6.1.1 Photoacoustic Spectroscopy 2929.6.1.2 Photorefractive Spectroscopy 2939.6.2 Single-Molecule Spectroscopy 2949.6.3 Fluorescence Correlation Spectroscopy 2969.6.4 X-ray Techniques 297References 29910 Interconversion of Light and Chemical Energy by Bimolecular Redox Processes 30510.1 Light as a Reactant 30510.2 Light as a Product 30610.3 Conversion of Light into Chemical Energy 30710.4 Conversion of Chemical Energy into Light: Chemiluminescence 30910.5 Conversion of Chemical Energy into Light: Electrochemiluminescence 30910.6 Light Absorption Sensitizers 31010.7 Light Emission Sensitizers 31210.8 Oscillating Chemiluminescence 314References 31511 Photocatalysis 31711.1 Photocatalytic Processes 31711.2 Photocatalysis in Organic Synthesis 31911.2.1 Photoredox Catalysis 32111.2.1.1 Reductive Dehalogenation Catalyzed by Visible Light 32211.2.1.2 Merging Photocatalytic and Organocatalytic Cycles 32211.2.2 Two-Photon-Driven Photoredox Catalysis 32211.2.3 Direct Photocatalyzed Hydrogen Transfer 32711.3 Heterogeneous Photocatalysis 33011.4 Photocatalysis in Environmental Protection 33111.4.1 Principles 33111.4.2 Solar Disinfection (SODIS) 33111.4.3 Photo-assisted Fenton Reaction 33211.4.4 Photocatalytic Pollution Remediation 332References 33312 Light-Powered Molecular Devices and Machines 33912.1 Introduction 33912.2 The Role of Light 34012.3 Molecular Devices for Information Processing 34212.3.1 Photochromic Systems as Molecular Memories 34212.3.2 Molecular Logics 34312.3.2.1 Luminescent Sensors as Simple Logic Gates 34312.3.2.2 AND Logic Gate 34412.3.2.3 Encoding and Decoding 34412.4 Molecular Devices Based on Energy Transfer 34612.4.1 Wires 34612.4.2 Switches 34812.4.3 Plug/Socket Systems 34912.4.4 Light-Harvesting Antennas 35012.5 Molecular Devices Based on Electron Transfer 35412.5.1 Wires 35412.5.2 Switches 36012.5.3 Extension Cables 36212.6 Light-Powered Molecular Machines 36312.6.1 Basic Remarks 36312.6.2 Rotary Motors Based on cis–trans Photoisomerization 36512.6.3 Photochemically Driven Threading/Dethreading Movements 36712.6.4 Molecular Pumps 37212.6.5 Molecular Shuttles and Related Systems 37312.6.5.1 An Artificial, Autonomous, Solar Light-Powered Molecular Motor 37312.6.5.2 Three-Station Rotaxanes 37612.6.5.3 Rotaxanes as Carriers 37712.6.6 Molecular Walkers 37712.6.7 Unidirectional Rotation in Catenanes 38012.6.8 Photocontrolled Valves, Boxes, and Related Systems 383References 38513 Natural and Artificial Photosynthesis 39513.1 Energy for Spaceship Earth 39513.2 Natural Photosynthesis 39713.2.1 Light Harvesting: Absorption and Energy Transfer 39813.2.2 Photoinduced Electron Transfer Leading to Charge Separation 39813.2.2.1 Bacterial Photosynthesis 39813.2.2.2 Green Plants Photosynthesis 40013.2.3 Efficiency of Photosynthesis 40213.3 Artificial Photosynthesis 40413.3.1 Water Splitting by Photocatalytic Semiconductor Nanoparticles 40813.3.2 Water Splitting in Photoelectrochemical Cells 411References 41514 Photochemistry and Photophysics in Biologically Relevant Processes 42114.1 Introduction 42114.2 Vision 42114.2.1 Basic Principle 42114.2.2 Primary Photochemical Events 42314.3 Light, Skin, and Sunscreens 42314.4 Photochemical Damage in Living Systems 42414.4.1 Photochemical Damage to DNA 42414.4.2 Photochemical Damage to Proteins 42514.5 Therapeutic Strategies Using Light 42614.5.1 Phototherapy 42614.5.2 Photodynamic Therapy 42614.5.3 Photoactivated Chemotherapy 42814.6 DNA Photocleavage and Charge Transport 43214.6.1 Photocleaving Agents of Nucleic Acid 43214.6.2 Photoinduced Electron-Transfer Processes in DNA 43314.7 Fluorescence 43314.8 Luminescent Sensors 43414.8.1 Principles 43414.8.2 Amplifying Signal 43514.8.3 Oxygen Sensing and Bioimaging 43614.8.4 Voltage Neuron Sensor 43714.8.5 Measuring Blood Analytes 43914.9 Bioluminescence 440References 44215 Technological Applications of Photochemistry and Photophysics 44715.1 Introduction 44715.2 Photochromism 44715.3 Luminescent Sensors 45015.3.1 Wind Tunnel Research 45015.3.2 Thermometers 45115.3.3 Detecting Warfare Chemical Agents 45315.3.4 Detecting Explosives 45515.4 Optical Brightening Agents 45715.5 Atmospheric Photochemistry 45715.5.1 Natural Processes Involving Oxygen 45715.5.2 Ozone Hole 45815.6 Solar Cells 45915.6.1 Inorganic Photovoltaic (PV) Cells 45915.6.2 Organic Solar Cells (OSCs) 46215.6.3 Dye-Sensitized Solar Cells (DSSCs) 46315.7 Electroluminescent Materials 46515.7.1 Light-Emitting Diodes (LEDs) 46515.7.2 Organic Light-Emitting Diodes (OLEDs) 46615.7.3 Light-Emitting Electrochemical Cells (LECs) 46715.8 Polymers and Light 46915.8.1 Photopolymerization 46915.8.2 Photodegradation 47015.8.3 Stabilization of Commercial Polymers 47015.8.4 Photochemical Curing 47115.8.5 Other Light-Induced Processes 47115.8.6 Photolithography 47215.8.7 Stereolithography 47315.8.8 Holography 47415.9 Light for Chemical Synthesis 47515.9.1 Photochlorination of Polymers 47615.9.2 Synthesis of Caprolactam 47615.9.3 Synthesis of Vitamins 47615.9.4 Perfumes 477References 47816 Research Frontiers 48516.1 Introduction 48516.2 Luminescent First-Row Transition Metal Complexes 48516.2.1 Luminescent Cr(III) and V(III) Complexes 48516.2.2 Luminescent Cu(I) Complexes 48616.3 Aggregation-Induced Emission 48916.4 TADF Chromophores 49416.5 Photoactivated Molecular Machine 49516.6 Photoactivated Molecular Tweezer in a Multifunctional Compound 49816.7 Singlet Fission 49916.8 Chirality-Induced Spin Selectivity in Electron Donor–Acceptor Dyads 50316.9 Photocatalytic Water Splitting 504References 506Index 511