Molecular Fluorescence

This second edition of the well-established bestseller is completely updated and revised with approximately 30 % additional material, including two new chapters on applications, which has seen the most significant developments.

The comprehensive overview written at an introductory level covers fundamental aspects, principles of instrumentation and practical applications, while providing many valuable tips.

For photochemists and photophysicists, physical chemists, molecular physicists, biophysicists, biochemists and biologists, lecturers and students of chemistry, physics, and biology.

Bernard Valeur received his engineering diploma from the Ecole Superieure de Physique et de Chimie Industrielles de Paris (E.S.P.C.I.) and his PhD degree from the Universite Pierre-et-Marie-Curie (Paris, France), followed by postdoctoral research at the University of Illinois at Urbana-Champaign (USA). After being an associate professor at E.S.P.C.I, he became full professor of physical chemistry at the Conservatoire National des Arts et Metiers (Paris) in 1979, where he is emeritus professor since 2008. Professor Valeur is a member of the laboratory Photophysique et Photochimie Supramoleculaires et Macromoleculaires at the Ecole Normale Superieure de Cachan since 1996. From 1995 to 2000 he served as an elected member of the French Comite National de la Recherche Scientifique. He is the winner of the 2012 Gregorio Weber Award for Excellence in Fluorescence Theory and Applications and author of over 170 articles or book chapters, five books, and the editor of one book. In addition, he is a member of several editorial boards.

Mario Nuno Berberan-Santos graduated in chemical engineering from Instituto Superior Tecnico (IST, Technical University of Lisbon, Portugal). After a brief stay at the National Research Council of Canada (Ottawa), he received his PhD in chemistry from IST in 1989. He was a post-doctoral fellow with Bernard Valeur at Conservatoire National des Arts et Metiers (Paris, France), and at Laboratoire pour l'Utilisation du Rayonnement Electromagnetique (Univ. Paris-Sud, Orsay, France). He is full professor of Physical Chemistry at IST, and was invited full professor at the Ecole Normale Superieure de Cachan (France). He is a member of several editorial advisory boards and is president of the Portuguese Chemical Society (2010-2012). He has authored over 180 publications, including 150 papers in scientific journals, several book chapters, and was the editor of one book.

Preface to the First Edition XV

Preface to the Second Edition XVII

Acknowledgments XIX

Prologue XXI

1 Introduction 1

1.1 What Is Luminescence? 1

1.2 A Brief History of Fluorescence and Phosphorescence 2

1.2.1 Early Observations 3

1.2.2 On the Distinction between Fluorescence and Phosphorescence: Decay Time Measurements 10

1.2.3 The Perrin–Jablonski Diagram 12

1.2.4 Fluorescence Polarization 14

1.2.5 Resonance Energy Transfer 16

1.2.6 Early Applications of Fluorescence 17

1.3 Photoluminescence of Organic and Inorganic Species: Fluorescence or Phosphorescence? 19

1.4 Various De-Excitation Processes of Excited Molecules 20

1.5 Fluorescent Probes, Indicators, Labels, and Tracers 21

1.6 Ultimate Temporal and Spatial Resolution: Femtoseconds, Femtoliters, Femtomoles, and Single-Molecule Detection 23

General Bibliography: Monographs and Books 25

Part I Principles 31

2 Absorption of Ultraviolet, Visible, and Near-Infrared Radiation 33

2.1 Electronic Transitions 33

2.2 Transition Probabilities: The Beer–Lambert Law, Oscillator Strength 39

2.3 Selection Rules 46

2.4 The Franck–Condon Principle 47

2.5 Multiphoton Absorption and Harmonic Generation 49

Bibliography 51

3 Characteristics of Fluorescence Emission 53

3.1 Radiative and Nonradiative Transitions between Electronic States 53

3.1.1 Internal Conversion 56

3.1.2 Fluorescence 56

3.1.3 Intersystem Crossing and Subsequent Processes 57

3.1.3.1 Intersystem Crossing 58

3.1.3.2 Phosphorescence versus Nonradiative De-Excitation 60

3.1.3.3 Delayed Fluorescence 60

3.1.3.4 Triplet–Triplet Transitions 61

3.2 Lifetimes and Quantum Yields 61

3.2.1 Excited-State Lifetimes 61

3.2.2 Quantum Yields 64

3.2.3 Effect of Temperature 66

3.3 Emission and Excitation Spectra 67

3.3.1 Steady-State Fluorescence Intensity 67

3.3.2 Emission Spectra 68

3.3.3 Excitation Spectra 71

3.3.4 Stokes Shift 72

Bibliography 74

4 Structural Effects on Fluorescence Emission 75

4.1 Effects of the Molecular Structure of Organic Molecules on Their Fluorescence 75

4.1.1 Extent of the π-Electron System: Nature of the Lowest-Lying Transition 75

4.1.2 Substituted Aromatic Hydrocarbons 77

4.1.2.1 Internal Heavy Atom Effect 77

4.1.2.2 Electron-Donating Substituents: –OH, –OR, –NH2, –NHR, –NR2 78

4.1.2.3 Electron-Withdrawing Substituents: Carbonyl and Nitro Compounds 78

4.1.2.4 Sulfonates 79

4.1.3 Heterocyclic Compounds 80

4.1.3.1 Compounds with Heteronitrogen Atoms 80

4.1.3.2 Coumarins 81

4.1.3.3 Xanthenic Dyes 82

4.1.3.4 Oxazines 84

4.1.3.5 Cyanines 85

4.1.3.6 BODIPY Fluorophores 86

4.1.4 Compounds Undergoing Photoinduced ICT and Internal Rotation 87

4.2 Fluorescence of Conjugated Polymers (CPs) 92

4.3 Luminescence of Carbon Nanostructures: Fullerenes, Nanotubes, and Carbon Dots 93

4.4 Luminescence of Metal Compounds, Metal Complexes, and Metal Clusters 96

4.5 Luminescence of Semiconductor Nanocrystals (Quantum Dots and Quantum Rods) 103

Bibliography 105

5 Environmental Effects on Fluorescence Emission 109

5.1 Homogeneous and Inhomogeneous Band Broadening – Red-Edge Effects 109

5.2 General Considerations on Solvent Effects 110

5.3 Solvent Relaxation Subsequent to Photoinduced Charge Transfer (PCT) 112

5.4 Theory of Solvatochromic Shifts 117

5.5 Effects of Specifi c Interactions 119

5.5.1 Effects of Hydrogen Bonding on Absorption and Fluorescence Spectra 119

5.5.2 Examples of Effects of Specifi c Interactions 120

5.5.3 Polarity-Induced Inversion of n−π* and π−π* States 123

5.6 Empirical Scales of Solvent Polarity 124

5.6.1 Scales Based on Solvatochromic Shifts 124

5.6.1.1 Single-Parameter Approach 124

5.6.1.2 Multiparameter Approach 126

5.6.2 Scale Based on Polarity-Induced Changes in Vibronic Bands (Py Scale) 129

5.7 Viscosity Effects 129

5.7.1 What is Viscosity? Significance at a Microscopic Level 129

5.7.2 Viscosity Effect on the Fluorescence of Molecules Undergoing Internal Rotations 132

5.8 Fluorescence in Solid Matrices at Low Temperature 135

5.8.1 Shpol’skii Spectroscopy 136

5.8.2 Matrix Isolation Spectroscopy 137

5.8.3 Site-Selection Spectroscopy 137

5.9 Fluorescence in Gas Phase: Supersonic Jets 137

Bibliography 138

6 Effects of Intermolecular Photophysical Processes on Fluorescence Emission 141

6.1 Introduction 141

6.2 Overview of the Intermolecular De-Excitation Processes of Excited Molecules Leading to Fluorescence Quenching 143

6.2.1 Phenomenological Approach 143

6.2.2 Dynamic Quenching 146

6.2.2.1 Stern–Volmer Kinetics 146

6.2.2.2 Transient Effects 148

6.2.3 Static Quenching 152

6.2.3.1 Sphere of Effective Quenching 152

6.2.3.2 Formation of a Ground-State Nonfluorescent Complex 153

6.2.4 Simultaneous Dynamic and Static Quenching 154

6.2.5 Quenching of Heterogeneously Emitting Systems 158

6.3 Photoinduced Electron Transfer 159

6.4 Formation of Excimers and Exciplexes 162

6.4.1 Excimers 163

6.4.2 Exciplexes 167

6.5 Photoinduced Proton Transfer 168

6.5.1 General Equations for Deprotonation in the Excited State 170

6.5.2 Determination of the Excited-State pK* 172

6.5.2.1 Prediction by Means of the Förster Cycle 172

6.5.2.2 Steady-State Measurements 173

6.5.2.3 Time-Resolved Experiments 174

6.5.3 pH Dependence of Absorption and Emission Spectra 174

6.5.4 Equations for Bases Undergoing Protonation in the Excited State 178

Bibliography 179

7 Fluorescence Polarization: Emission Anisotropy 181

7.1 Polarized Light and Photoselection of Absorbing Molecules 181

7.2 Characterization of the Polarization State of Fluorescence (Polarization Ratio and Emission Anisotropy) 184

7.2.1 Excitation by Polarized Light 184

7.2.1.1 Vertically Polarized Excitation 184

7.2.1.2 Horizontally Polarized Excitation 186

7.2.2 Excitation by Natural Light 187

7.3 Instantaneous and Steady-State Anisotropy 187

7.3.1 Instantaneous Anisotropy 187

7.3.2 Steady-State Anisotropy 188

7.4 Additivity Law of Anisotropy 188

7.5 Relation between Emission Anisotropy and Angular Distribution of the Emission Transition Moments 190

7.6 Case of Motionless Molecules with Random Orientation 191

7.6.1 Parallel Absorption and Emission Transition Moments 191

7.6.2 Nonparallel Absorption and Emission Transition Moments 192

7.6.3 Multiphoton Excitation 196

7.7 Effect of Rotational Motion 199

7.7.1 Free Rotations 200

7.7.1.1 General Equations 200

7.7.1.2 Isotropic Rotations 201

7.7.1.3 Anisotropic Rotations 203

7.7.2 Hindered Rotations 206

7.8 Applications 207

Bibliography 210

8 Excitation Energy Transfer 213

8.1 Introduction 213

8.2 Distinction between Radiative and Nonradiative Transfer 218

8.3 Radiative Energy Transfer 219

8.4 Nonradiative Energy Transfer 221

8.4.1 Interactions Involved in Nonradiative Energy Transfer 221

8.4.2 The Three Main Classes of Coupling 224

8.4.3 Förster’s Formulation of Long-Range Dipole–Dipole Transfer (Very Weak Coupling) 226

8.4.4 Dexter’s Formulation of Exchange Energy Transfer (Very Weak Coupling) 233

8.4.5 Selection Rules 233

8.5 Determination of Distances at a Supramolecular Level Using FRET 235

8.5.1 Single Distance between the Donor and the Acceptor 235

8.5.2 Distributions of Distances in Donor–Acceptor Pairs 239

8.5.3 Single Molecule Studies 242

8.5.4 On the Validity of Förster’s Theory for the Estimation of Distances 242

8.6 FRET in Ensembles of Donors and Acceptors 243

8.6.1 FRET in Three Dimensions: Effect of Viscosity 243

8.6.2 Effects of Dimensionality on FRET 247

8.6.3 Effects of Restricted Geometries on FRET 250

8.7 FRET between Like Molecules: Excitation Energy Migration in Assemblies of Chromophores 250

8.7.1 FRET within a Pair of Like Chromophores 251

8.7.2 FRET in Assemblies of Like Chromophores 251

8.7.3 Lack of Energy Transfer upon Excitation at the Red Edge of the Absorption Spectrum (Weber’s Red-Edge Effect) 252

8.8 Overview of Qualitative and Quantitative Applications of FRET 252

Bibliography 258

Part II Techniques 263

9 Steady-State Spectrofl uorometry 265

9.1 Operating Principles of a Spectrofl uorometer 265

9.2 Correction of Excitation Spectra 268

9.3 Correction of Emission Spectra 268

9.4 Measurement of Fluorescence Quantum Yields 269

9.5 Possible Artifacts in Spectrofl uorometry 271

9.5.1 Inner Filter Effects 271

9.5.1.1 Excitation Inner Filter Effect 271

9.5.1.2 Emission Inner Filter Effect (Self-Absorption) 272

9.5.1.3 Inner Filter Effects due to the Presence of Other Substances 274

9.5.2 Autofl uorescence 274

9.5.3 Polarization Effects 275

9.5.4 Effect of Oxygen 275

9.5.5 Photobleaching Effect 276

9.6 Measurement of Steady-State Emission Anisotropy: Polarization Spectra 277

9.6.1 Principles of Measurement 277

9.6.2 Possible Artifacts 279

9.6.3 Tests Prior to Fluorescence Polarization Measurements 279

Appendix 9.A Elimination of Polarization Effects in the Measurement of Fluorescence Intensity 281

Bibliography 283

10 Time-Resolved Fluorescence Techniques 285

10.1 Basic Equations of Pulse and Phase-Modulation Fluorimetries 286

10.1.1 Pulse Fluorimetry 286

10.1.2 Phase-Modulation Fluorimetry 286

10.1.3 Relationship between Harmonic Response and δ-Pulse Response 287

10.1.4 General Relations for Single Exponential and MultiExponential Decays 290

10.2 Pulse Fluorimetry 292

10.2.1 Light Sources 292

10.2.2 Single-Photon Timing Technique (10 ps–500 μs) 292

10.2.3 Streak Camera (1 ps–10 ns) 294

10.2.4 Fluorescence Upconversion (0.1–500 ps) 295

10.2.5 Optical Kerr-Gating (0.1–500 ps) 297

10.3 Phase-Modulation Fluorimetry 298

10.3.1 Introduction 298

10.3.2 Phase Fluorimeters Using a Continuous Light Source and an Electro-Optic Modulator 300

10.3.3 Phase Fluorimeters Using the Harmonic Content of a Pulsed Laser 302

10.4 Artifacts in Time-Resolved Fluorimetry 302

10.4.1 Inner Filter Effects 302

10.4.2 Dependence of the Instrument Response on Wavelength – Color Effect 304

10.4.3 Polarization Effects 304

10.4.4 Effects of Light Scattering 304

10.5 Data Analysis 305

10.5.1 Pulse Fluorimetry 305

10.5.2 Phase-Modulation Fluorimetry 306

10.5.3 Judging the Quality of the Fit 306

10.5.4 Global Analysis 307

10.5.5 Fluorescence Decays with Underlying Distributions of Decay Times 308

10.6 Lifetime Standards 312

10.7 Time-Resolved Polarization Measurements 314

10.7.1 General Equations for Time-Dependent Anisotropy and Polarized Components 314

10.7.2 Pulse Fluorimetry 315

10.7.3 Phase-Modulation Fluorimetry 317

10.7.4 Reference Compounds for Time-Resolved Fluorescence Anisotropy Measurements 318

10.8 Time-Resolved Fluorescence Spectra 318

10.9 Lifetime-Based Decomposition of Spectra 318

10.10 Comparison between Single-Photon Timing Fluorimetry and Phase-Modulation Fluorimetry 322

Bibliography 323

11 Fluorescence Microscopy 327

11.1 Wide-Field (Conventional), Confocal, and Two-Photon Fluorescence Microscopies 328

11.1.1 Wide-Field (Conventional) Fluorescence Microscopy 328

11.1.2 Confocal Fluorescence Microscopy 329

11.1.3 Two-Photon Excitation Fluorescence Microscopy 331

11.1.4 Fluorescence Polarization Measurements in Microscopy 333

11.2 Super-Resolution (Subdiffraction) Techniques 333

11.2.1 Scanning Near-Field Optical Microscopy (SNOM) 333

11.2.2 Far-Field Techniques 337

11.3 Fluorescence Lifetime Imaging Microscopy (FLIM) 340

11.3.1 Time-Domain FLIM 341

11.3.2 Frequency-Domain FLIM 342

11.4 Applications 342

Bibliography 346

12 Fluorescence Correlation Spectroscopy and Single-Molecule Fluorescence Spectroscopy 349

12.1 Fluorescence Correlation Spectroscopy (FCS) 349

12.1.1 Conceptual Basis and Instrumentation 350

12.1.2 Determination of Translational Diffusion Coefficients 355

12.1.3 Chemical Kinetic Studies 356

12.1.4 Determination of Rotational Diffusion Coefficients 359

12.1.5 Cross-Correlation Methods 360

12.2 Single-Molecule Fluorescence Spectroscopy 360

12.2.1 General Remarks 360

12.2.2 Single-Molecule Detection in Flowing Solutions 361

12.2.3 Single-Molecule Detection Using Fluorescence Microscopy Techniques 363

12.2.4 Single-Molecule and Single-Particle Photophysics 367

12.2.5 Applications and Usefulness of Single-Molecule Fluorescence 371

Bibliography 372

Part III Applications 377

13 Evaluation of Local Physical Parameters by Means of Fluorescent Probes 379

13.1 Fluorescent Probes for Polarity 379

13.1.1 Examples of Photoinduced Charge Transfer (PCT) Probes for Polarity 380

13.1.2 Pyrene and Its Derivatives 384

13.2 Estimation of “Microviscosity,” Fluidity, and Molecular Mobility 384

13.2.1 Various Methods 385

13.2.2 Use of Molecular Rotors 386

13.2.3 Methods Based on Intermolecular Quenching or Intermolecular Excimer Formation 389

13.2.4 Methods Based on Intramolecular Excimer Formation 390

13.2.5 Fluorescence Polarization Method 393

13.2.5.1 Choice of Probes 393

13.2.5.2 Homogeneous Isotropic Media 393

13.2.5.3 Ordered Systems 395

13.2.5.4 Practical Aspects 395

13.2.6 Concluding Remarks 397

13.3 Temperature 398

13.4 Pressure 402

Bibliography 404

14 Chemical Sensing via Fluorescence 409

14.1 Introduction 409

14.2 Various Approaches of Fluorescence Sensing 410

14.3 Fluorescent pH Indicators 412

14.3.1 Principles 412

14.3.2 The Main Fluorescent pH Indicators 417

14.3.2.1 Coumarins 417

14.3.2.2 Pyranine 417

14.3.2.3 Fluorescein and Its Derivatives 419

14.3.2.4 SNARF and SNAFL 419

14.3.2.5 pH Indicators Based on Photoinduced Electron Transfer (PET) 420

14.4 Design Principles of Fluorescent Molecular Sensors Based on Ion or Molecule Recognition 420

14.4.1 General Aspects 420

14.4.2 Recognition Units and Topology 422

14.4.3 Photophysical Signal Transduction 424

14.4.3.1 Photoinduced Electron Transfer (PET) 424

14.4.3.2 Photoinduced Charge Transfer (PCT) 425

14.4.3.3 Excimer Formation or Disappearance 427

14.4.3.4 Förster Resonance Energy Transfer (FRET) 427

14.5 Fluorescent Molecular Sensors of Metal Ions 427

14.5.1 General Aspects 427

14.5.2 Fluorescent PET Cation Sensors 430

14.5.3 Fluorescent PCT Cation Sensors 430

14.5.4 Excimer-Based Cation Sensors 430

14.5.5 Cation Sensors Based on FRET 430

14.5.6 Hydroxyquinoline-Based Cation Sensors 432

14.5.7 Concluding Remarks on Cation Sensors 435

14.6 Fluorescent Molecular Sensors of Anions 436

14.6.1 Anion Sensors Based on Collisional Quenching 437

14.6.2 Anion Sensors Based on Fluorescence Changes upon Anion Binding 437

14.6.2.1 Urea and Thiourea Groups 438

14.6.2.2 Pyrrole Groups 439

14.6.2.3 Polyazaalkanes 440

14.6.2.4 Imidazolium Groups 443

14.6.2.5 Anion Binding by Metal Ion Complexes 443

14.6.3 Anion Sensors Based on the Displacement of a Competitive Fluorescent Anionic Molecule 444

14.7 Fluorescent Molecular Sensors of Neutral Molecules 445

14.7.1 Cyclodextrin-Based Fluorescent Sensors 446

14.7.2 Boronic Acid-Based Fluorescent Sensors 449

14.7.3 Porphyrin-Based Fluorescent Sensors 452

14.8 Fluorescence Sensing of Gases 453

14.8.1 Oxygen 453

14.8.2 Carbon Dioxide 456

14.8.3 Nitric Oxide 456

14.8.4 Explosives 456

14.9 Sensing Devices 458

14.10 Remote Sensing by Fluorescence LIDAR 460

14.10.1 Vegetation Monitoring 461

14.10.2 Marine Monitoring 462

14.10.3 Historic Monuments 462

Appendix 14.A. Spectrophotometric and Spectrofluorometric pH Titrations 462

Single-Wavelength Measurements 462

Dual-Wavelength Measurements 463

Appendix 14.B. Determination of the Stoichiometry and Stability Constant of Metal Complexes from Spectrophotometric or Spectrofluorometric Titrations 465

Definition of the Equilibrium Constants 465

Preliminary Remarks on Titrations by Spectrophotometry and Spectrofluorometry 467

Formation of a 1 : 1 Complex (Single-Wavelength Measurements) 467

Formation of a 1 : 1 Complex (Dual-Wavelength Measurements) 469

Formation of Successive Complexes ML and M2L 470

Cooperativity 471

Determination of the Stoichiometry of a Complex by the Method of Continuous Variations (Job’s Method) 471

Bibliography 473

15 Autofluorescence and Fluorescence Labeling in Biology and Medicine 479

15.1 Introduction 479

15.2 Natural (Intrinsic) Chromophores and Fluorophores 480

15.2.1 Amino Acids and Derivatives 481

15.2.2 Coenzymes 488

15.2.3 Chlorophylls 490

15.3 Fluorescent Proteins (FPs) 491

15.4 Fluorescent Small Molecules 493

15.5 Quantum Dots and Other Luminescent Nanoparticles 497

15.6 Conclusion 501

Bibliography 502

16 Miscellaneous Applications 507

16.1 Fluorescent Whitening Agents 507

16.2 Fluorescent Nondestructive Testing 508

16.3 Food Science 511

16.4 Forensics 513

16.5 Counterfeit Detection 514

16.6 Fluorescence in Art 515

Bibliography 518

Appendix: Characteristics of Fluorescent Organic Compounds 521

Epilogue 551

Index 553