Principles and Applications of Photochemistry

Preface xiii

1 Introductory Concepts 1

Aims and Objectives 1

1.1 The Quantum Nature of Matter and Light 2

1.2 Modelling Atoms: Atomic Orbitals 6

1.3 Modelling Molecules: Molecular Orbitals 9

1.4 Modelling Molecules: Electronic States 13

1.5 Light Sources Used in Photochemistry 16

1.6 Efficiency of Photochemical Processes: Quantum Yield 25

2 Light Absorption and Electronically-excited States 29

Aims and Objectives 29

2.1 Introduction 29

2.2 The Beer-Lambert Law 30

2.3 The Physical Basis of Light Absorption by Molecules 32

2.4 Absorption of Light by Organic Molecules 35

2.5 Linearly-conjugated Molecules 39

2.6 Some Selection Rules 42

2.7 Absorption of Light by Inorganic Complexes 43

3 The Physical Deactivation of Excited States 47

Aims and Objectives 47

3.1 Introduction 47

3.2 Jablonski Diagrams 49

3.3 Excited-state Lifetimes 53

4 Radiative Processes of Excited States 59

Aims and Objectives 59

4.1 Introduction 60

4.2 Fluorescence and Fluorescence Spectra 61

4.3 An Exception to Kasha's Rule 63

4.4 Fluorescence Quantum Yield 64

4.5 Factors Contributing to Fluorescence Behaviour 65

4.6 Molecular Fluorescence in Analytical Chemistry 67

4.7 Phosphorescence 70

4.8 Delayed Fluorescence 73

4.9 Lanthanide Luminescence 74

5 Intramolecular Radiationless Transitions of Excited States 77

Aims and Objectives 77

5.1 Introduction 77

5.2 The Energy Gap Law 79

5.3 The Franck-Condon Factor 79

5.4 Heavy Atom Effects on Intersystem Crossing 82

5.5 El-Sayed's Selection Rules for Intersystem Crosssing 83

6 Intermolecular Physical Processes of Excited States 87

Aims and Objectives 87

6.1 Quenching Processes 88

6.2 Excimers 90

6.3 Exciplexes 93

6.4 Intermolecular Electronic Energy Transfer 96

6.5 The Trivial or Radiative Mechanism of Energy Transfer 97

6.6 Long-range Dipole-Dipole (Coulombic) Energy Transfer 98

6.7 Short-range Electron-exchange