Chromic Phenomena

Technological Applications of Colour

Chemistry

Second Edition

Peter Bamfield

Consultant, Penarth, UK

Michael G. HutchingsDyStar UK Ltd, Manchester, UK

RSC Publishing

Contents

Introduction 1

Chapter 1 Phenomena Involving a Stimulated Colour Change 9

1.1 Introduction 9

1.2 Photochromism 12

1.2.1 Main Chemical Classes 13

1.2.2 Spirobenzopyrans 14

1.2.3 Spironaphthoxazines 15

1.2.4 Benzo- and Naphthopyrans (Chromenes) 17

1.2.5 Fulgides 21

1.2.6 Diarylethenes 23

1.2.6.1 Gated Photochromism in

Diarylethenes 27

1.2.7 Miscellaneous Photochromic Systems 28

1.2.7.1 Azobenzenes 28

1.2.7.2 Other Organic Photochromes 29

1.2.7.3 Inorganic Photochromes 31

1.2.7.4 Biological Photochromes 32

1.2.7.5 Polymers, Matrices and AmorphousMaterials 33

1.2.8 Applications of Photochromic Materials 35

1.2.8.1 Applications in Ophthalmics 36

1.2.8.2 Novelty Items, Fashion, Cosmetics

and Security 38

1.2.8.3 Optical Memories and Switches 39

1.2.8.4 Other Optical Applications 46

1.2.8.5 Biological and Bio-medical

Applications 46

Chromic Phenomena: Technological Applications of Colour Chemistry, Second Edition

By Peter Bamfield and Michael G. Hutchings

© Peter Bamfield and Michael G. Hutchings 2010

Published by the Royal Society of Chemistry, www.rsc.org

1.3 Thermochromism 47

1.3.1 Inorganic and Organometallic Materials 48

1.3.2 Reversible Intrinsically Thermochromic

Organic Systems 49

1.3.2.1 Molecular Rearrangements 49

1.3.2.2 Stereoisomerism 50

1.3.2.3 Macromolecular Systems 51

1.3.3 Reversible Indirect Thermochromic Systems 53

1.3.3.1 Composite Thermochromic Pigments 53

1.3.3.2 Chromogenic Gels 55

1.3.4 Applications of Thermochromic Materials 56

1.3.4.1 Paints, Plastics and Textiles 56

1.3.4.2 Architectural Uses 58

1.4 Ionochromism 59

1.4.1 Ionochromic Compounds 59

1.4.1.1 Phthalides 59

1.4.1.2 Leuco Di-and Tri-arylmethanes 61

1.4.1.3 Fluorans 62

1.4.1.4 Azo and Styryl Dyes 62

1.4.1.5 Metallochromism in Chelates and

Crown Ethers 63

1.4.1.6 Chromogenic Anion Sensors and

Metallochromism 65

1.4.2 Applications of Ionochromism 69

1.4.2.1 Analytical Chemistry 69

1.4.2.2 Absorbance-based Ion-selective

Optical Sensors 71

1.4.2.3 Carbonless Copying Paper 73

1.4.2.4 Direct Thermal Printing 75

1.5 Electrochromism 76

1.5.1 Electrochromic Cells 76

1.5.2 Electrochrome Types 78

1.5.2.1 Solution Electrochromes (Type-I) 78

1.5.2.2 Solution-Solid Electrochromes

(Type-II) 78

1.5.2.3 Solid Electrochromes (Type-Ill) 78

1.5.3 Electrochromic Chemicals 79

1.5.3.1 Inorganic Oxides 79

1.5.3.2 Prussian Blue and Metal Hexacyano-metallates 80

1.5.3.3 Metal Phthalocyanines 80

1.5.3.4 Viologens (4,4'-bipyridylium salts) 81

1.5.3.5 Polymeric Electrochromes 82

1.5.3.6 Other Organic Electrochromes 85

1.5.4 Applications of Electrochromism 86

1.5.4.1 Rear-view Mirrors 86

1.5.4.2 Smart Windows - Chromogenic

Glazing 87

1.5.4.3 Displays 91

1.6 Gasocliromism 92

1.7 Solvatochromism 96

1.7.1 Solvent Polarity and Solvatochromic Shifts 96

1.7.2 Applications of Solvatochromism 99

1.7.2.1 Analysis of Liquids 99

1.7.2.2 Polymers and Polymer-bound Probes 100

1.7.2.3 Biological Probes and Solvatofluoro-

chromism 100

1.8 Vapochromism 100

1.8.1 Vapochromic Materials 101

1.8.2 Vapochromic Sensors for VOCs and Their

Applications 102

1.9 Mechanochromism 104

1.9.1 Piezochromism 104

1.9.2 Tribochromism 105

1.9.3 Applications of Mechanochromism 105

1.10 Chromic Phenomena via Aggregation 106

1.10.1 Excitonic Coupling 106

1.10.2 Examples of Excitonic Coupling Effects -

Aggregachromism 107

1.10.3 Crystallochromism 111

1.10.4 Excitonic Effects in Nature 112

1.11 Miscellaneous Chromisms 114

1.11.1 Amorphochromism 114

1.11.2 Chronochromism 114

1.11.3 Radiochromism 116

1.11.4 Magnetochromism 116

1.11.5 Biochromism 117

1.12 Colour Changes Due to Plasmonic Coupling 118

1.12.1 Metallic Nanoparticles 119

1.12.1.1 Properties ofMetallic Nanoparticles 120

1.12.2 Colour Change Applications of Metallic

Nanoparticles 122

1.12.3 Commercial Optical Biosensors Based on

Metallic Nanoparticles 125

Chapter 2 Phenomena Involving the Absorption and Reflectance

of Light 141

2.1 Introduction 141

2.2 Some Elements of Colour Physics Relating to Colorants 142

2.2.1 Additive Colour Mixing 142

2.2.2 Subtractive Colour Mixing 142

2.2.3 The CIE System 144

2.3 Classical Organic Dyes 145

2.3.1 Structural Classes 147

2.3.1.1 AzoDyestuffs 148

2.3.1.2 Cyclic and Polycyclic Quinones 156

2.3.1.3 Azines, Oxazines and Thiazines 161

2.3.1.4 Polymethines 161

2.3.1.5 Triarylcarbenium Dyes 163

2.3.1.6 Phthalocyanines 163

2.3.1.7 Sulfur Dyes 164

2.3.2 Application Processes 164

2.3.2.1 Dyeing and Printing of Textile Fibres 164

2.3.2.2 Paper 173

2.3.2.3 Leather 173

2.3.2.4 Food and Beverages 174

2.3.2.5 Hair Coloration 176

2.3.2.6 Biological Stains 178

2.4 Pigments 179

2.4.1 Organic Pigments 180

2.4.1.1 Azo Pigments 180

2.4.1.2 Metal Complexes 183

2.4.1.3 Benzimidazolones 183

2.4.1.4 Isoindolinone Pigments 184

2.4.1.5 Phthalocyanines 185

2.4.1.6 Quinacridones 186

2.4.1.7 Perylenes and Perinones 187

2.4.1.8 Polycyclic Quinones 187

2.4.1.9 Diketo-pyrrolopyrroles 188

2.4.1.10 Triarylcarbeniums 189

2.4.2 Inorganic Pigments 189

2.4.2.1 Iron Oxides 189

2.4.2.2 Chromium Oxide 190

2.4.2.3 Mixed Oxides 190

2.4.2.4 Alternatives for Cadmium Pigments 190

2.4.2.5 Chromate Pigments 191

2.4.2.6 Ultramarine Pigments 191

2.4.2.7 Iron Blue Pigments 191

2.4.3 Special Effect Pigments 192

2.4.4 Applications of Coloured Pigments 192

2.4.4.1 Dispersion of Pigments 193

2.4.4.2 Printing Inks 193

2.4.4.3 Paints and Coatings 194

2.4.4.4 Plastics 195

2.4.4.5 Construction Materials, Ceramics

and Glass 195

2.4.5 Nanoscale Pigments 196

2.4.5.1 Monodisperse Nanoscale Pigments 196

2.4.5.2 Core Shell Structures 197

2.5 Solvent Dyes 198

2.6 Dye Stabilisation via Molecular Encapsulation 199

2.6.1 Cyclodextrins and Related Rotaxanes 199

2.6.2 Inorganic Matrices 201

2.7 Natural Organic Colorants 202

2.7.1 Food and Cosmetics 202

2.7.2 Textiles and Leather 204

2.8 Photographic Colour Chemicals 206

2.8.1 Colour Photographic Processes 207

2.8.2 Colour Films and Papers 207

2.8.2.1 Colour Reversal and NegativeFilms 207

2.8.2.2 Colour Papers and Prints 208

2.8.3 Colour-forming Chemicals in Photography 208

2.9 Digital Printing 210

2.9.1 Ink-jet Printing 211

2.9.1.1 Continuous Ink-jet 211

2.9.1.2 Drop-on-Demand Ink-jet 211

2.9.1.3 Colorants for Ink-jet Printers 213

2.9.1.4 Commercial Applications of Ink-jetTechnology 217

2.9.2 Electrophotography 218

2.9.2.1 Materials for Electrophotography 220

2.9.2.2 Commercial Applications of Electro¬

photography 221

2.9.3 Thermal Transfer Printing 222

2.9.3.1 Thermal Wax Transfer 222

2.9.3.2 Dye Diffusion Thermal Transfer 224

2.9.3.3 No Ink Direct Thermal Printing 225

2.10 Electronic Paper and Flexible Displays 226

Chapter 3 Phenomena Involving Absorption of Energy Followed byEmission of Light 234

3.1 Introduction 234

3.2 Photoluminescence 1-Luminescent Pigments 236

3.2.1 Inorganic Phosphor Materials 238

3.2.1.1 Sulfides and Oxysulfides 238

3.2.1.2 Oxygen-dominant Phosphors 239

3.2.1.3 Silicates 239

3.2.2 Applications of Inorganic Phosphors 240

3.2.3 Up-conversion 242

3.2.3.1 Up-converting Rare Earth or

Anti-Stokes Materials 244

3.2.3.2 Applications of Up-converting

Phosphors - Securities 245

3.2.3.3 Up-converting Lasers 245

3.2.3.4 Emissive Displays Based on Up-

converting Phosphors 245

3.2.3.5 Optical Refrigeration 246

3.3 Cathodoluminescence 248

3.3.1 Cathode Ray Tubes 248

3.3.2 Field Emission Displays and Related 250

3.3.3 Radioluminescence 251

3.4 High-energy Photoluminescence 252

3.4.1 Lighting 252

3.4.2 Plasma Displays 253

3.4.3 Quantum Cutters 255

3.5 Photoluminescence 2 - Fluorescence 256

3.5.1 Fluorescent Chromophores - Fluorophores 258

3.5.1.1 Coumarins 258

3.5.1.2 Naphthalimides 259

3.5.1.3 Perylenes 259

3.5.1.4 Benzanthrones, Anthraquinones,Benzoxanthones and Benzothiox-

anthones 260

3.5.1.5 Xanthenes, Acridines and Oxazines 261

3.5.1.6 Hydrocarbons 262

3.5.1.7 Methines, Hemicyanines, Cyaninesand Oxonols 263

3.5.1.8 Dipyrromethines; Boraindacenes 264

3.5.1.9 Miscellaneous Chromophores 265

3.5.2 Luminescent Nanoparticles and Related

Materials 265

3.5.2.1 Semi-conductors - Quantum Dots,Silicon and Carbon 266

3.5.2.2 Organic Systems - Conjugated

Polymers, Dendrimers and Silica

Encapsulated Dyes 269

3.5.2.3 Metals and Metal Ions 272

3.5.3 Multi-photon Absorbers 276

3.5.4 Summary of Fluorescent and ComparableLuminescent Materials 278

3.5.5 Applications as Fluorescent Dyes, Pigmentsand Brighteners 282

3.5.5.1 Fluorescent Dyes in Textile

Applications 282

3.5.5.2 Daylight Fluorescent Pigments 282

3.5.5.3 Fluorescent Brightening Agents 283

3.5.5.4 Other Coloration Applications 283

3.5.6 Dye Lasers 284

3.5.6.1 Types of Dye Lasers 284

3.5.6.2 Mechanism of Dye Lasers 284

3.5.6.3 Laser Dyes 285

3.5.7 Analytical Applications of Fluorescence -

Sensors and Probes 286

3.5.7.1 Fluorophore and Analyte Interaction 286

3.5.8 Fluorescence in Optical Sensors 288

3.5.8.1 Optical Chemical Sensors for Medical

Application 289

3.5.8.2 Optical Biosensors 292

3.5.8.3 Optical Sensors for TemperatureMeasurements 295

3.5.8.4 Optical Noses 296

3.5.9 Fluorescent Probes and Labels in Biology and

Medicine 296

3.5.9.1 The NIR Transparency Window 296

3.5.9.2 Fluorophores in Bio-medical Imaging 298

3.5.9.3 Imaging and Tracking via

Fluorescence Switch-on 298

3.5.9.4 Composite Fluorophore-InorganicNanoparticles 299

3.5.9.5 Protein Walking 300

3.5.9.6 Quantum Dot Applications 300

3.5.9.7 Two-photon Microscopy in

Bio-medical Imaging 301

3.5.9.8 Up-conversion Nanophosphors for

in-vivo Animal Imaging 303

3.5.9.9 Fluorescent Labels for Proteomics

and Genomics 304

3.5.10 Biofluorescence 305

3.5.10.1 Green Fluorescent Protein 305

3.5.10.2 Applications of GFP 307

3.5.10.3 Phycobiliproteins 310

3.5.10.4 Fluorescent Probes in Flow

Cytometry 310

3.5.11 Fluorescent Probes and Indicators in Non-bio

Analysis 311

3.5.11.1 Fluorescent Oxygen Indicators in

Food Packaging 312

3.5.11.2 Fluorescent Materials in Forensics -

Fingerprint Detection 313

3.5.11.3 Luminescent Signalling via

Rigidochromism 313

3.5.12 Molecular Information Processors 315

3.6 Chemiluminescence 316

3.6.1 Chemiluminescent Reactions 317

3.6.1.1 Luminol Oxidation 317

3.6.1.2 Acridinium Compounds 318

3.6.1.3 Dioxetanes 318

3.6.2 Chemiluminescence Applications 319

3.6.2.1 Chemiluminescent Analysis 319

3.6.2.2 Chemiluminescent Lighting 320

3.7 Bioluminescence 321

3.7.1 Bioluminescent Systems 321

3.7.1.1 Firefly Luciferins 321

3.7.1.2 Bacterial Luciferases 322

3.7.1.3 Imidazopyrazine Luciferins and

Photoproteins 322

3.7.1.4 Dinoflagellates and Marine

"Phosphorescence" 323

3.7.2 Applications of Bioluminescence 323

3.7.2.1 Bioluminescence in Analysis 323

3.7.2.2 Bioluminescence Imaging 324

3.8 Electrochemiluminescence 324

3.8.1 The Chemistry of Electrochemiluminescence 325

3.8.2 Analytical Technology Based on Electrochemi¬

luminescence 326

3.9 Electroluminescence 328

3.9.1 Inorganic EL Materials and Displays 328

3.9.1.1 Powder EL (PEL) 329

3.9.1.2 Thin-film EL 329

3.9.2 Semi-conductor Light-emitting Diodes (LEDs) 331

3.9.3 LED Materials 332

3.9.4 Applications of LEDs 334

3.9.4.1 Coloured Lighting 334

3.9.4.2 White Lighting 335

3.9.4.3 Lighting for Displays 335

3.9.4.4 LED Displays 336

3.9.5 Organic Light-emitting Diodes - Introduction 336

3.9.6 Small Molecule OLEDs 337

3.9.6.1 Hole Transport Materials 338

3.9.6.2 Electron Transport Materials 339

3.9.6.3 Light-emitting Materials 339

3.9.6.4 Fluorescent Emitters as Hosts and

Dopants 340

3.9.6.5 Phosphorescent Dopants in

SMOLEDs 341

3.9.7 Polymer LEDS 344

3.9.7.1 Light-emitting Polymers (LEPs) 344

3.9.7.2 LEPs as Hosts for Phosphorescent

Dopants 346

xvii

3.9.8 Dendrimer LEDs 346

3.9.9 Applications of OLEDs in Displays 348

3.9.10 White Light OLEDS 350

3.9.10.1 Colour Mixing 351

3.9.10.2 Wavelength Conversion 351

3.9.10.3 Commercialisation of WOLEDs 353

3.10 Triboluminescence 353

3.11 Pyroluminescence 355

Chapter 4 Phenomena Involving Absorption of Light and EnergyTransfer 366

4.1 Introduction 366

4.2 Laser Addressable Compounds

(Infrared Absorbers) 367

4.2.1 Organic and Organometallic NIR Absorbers 368

4.2.1.1 Cyanines 369

4.2.1.2 Squarylium and Croconium Dyes 370

4.2.1.3 Iminium Salts 371

4.2.1.4 Triphenylmethanes 372

4.2.1.5 Nickel Dithiolenes 372

4.2.1.6 Quinones and Indoanilines 373

4.2.1.7 Perylenes and Related Structures 374

4.2.1.8 Phthalocyanines, Porphyrins and

Analogues 375

4.2.1.9 Donor-Acceptor Extended

Conjugated Molecules 377

4.2.2 Inorganic NIR Absorbers 379

4.2.3 Applications of Laser Addressable

Compounds and NIR Absorbers 379

4.2.3.1 Thermal Energy Conversion 380

4.2.3.2 Protection from IR Radiation 384

4.3 Optical Data Storage 386

4.3.1 Magneto-optic and Phase Change Media 387

4.3.2 Optical Data Storage Using Dyes 388

4.3.2.1 Recordable Media 388

4.3.2.2 Dye Requirements 389

4.3.2.3 Dye Classes 390

4.3.2.4 Dyes for High-density RecordingMedia 390

4.3.3 Developments in Optical Data Storage 392

4.4 Organic Photoconductors 393

4,4.1 Charge Generation Materials 395

4.4.1.1 Azo Pigments 395

4.4.1.2 Phthalocyanines 396

4.4.1.3 Other CGMs 396

4.4.2 Charge Transport Materials 397

4.5 Photosensitisers 398

4.5.1 Sensitisers in Photochemical Synthesis 399

4.5.2 Photoinitiation of Polymerisation 401

4.5.3 Sensitisers in Colour Photography 405

4.6 Sensitisers in Medicine and Chemical Biology 407

4.6.1 Photomedicine 409

4.6.2 Photodynamic Therapy 410

4.6.2.1 The Mechanism of PDT 412

4.6.2.2 Light Sources for PDT 412

4.6.2.3 Photosensitisers for PDT 412

4.6.3 PDT by Production of Nitric Oxide 419

4.6.4 Photothermal Therapy 420

4.6.5 Photodynamic Inactivation of Microbes and

Viruses 420

4.6.5.1 Photobactericides 424

4.6.5.2 Photoantivirals 424

4.6.6 Photoinsecticides 425

4.7 Photodecontamination 426

4.8 Solar Energy Utilisation 427

4.8.1 Solar Cells and Electrical Energy 427

4.8.1.1 Inorganic Photovoltaic Cells 428

4.8.1.2 Organic Solar Cells 430

4.8.1.3 Hybrid Solar Cells 435

4.8.1.4 Dye-sensitised Solar Cells 436

4.8.1.5 Commercialisation of Organic Solar

and DSCs 441

4.8.1.6 Solar Concentrators 442

4.8.2 Artificial Photosynthesis 443

4.8.2.1 Artificial Light-harvesting Antennae 444

4.8.2.2 Artificial Reaction Centres 446

4.8.2.3 Artificial Reaction Centre-Antenna

Couples 448

4.8.2.4 Transmembrane Pumping 449

4.8.3 The Production of Useful Chemicals and Fuels 451

4.8.3.1 Water Reduction/Splitting 451

4.8.3.2 Carbon Dioxide Photoreduction 453

4.8.3.3 Photobiological Processes 453

4.9 Conversion of Light into Kinetic Energy 455

Chapter 5 Chromic Phenomena Involving the Manipulation of Light 471

5.1 Introduction 471

5.2 Liquid Crystals 471

5.2.1 Nematic Liquid Crystals and Their Applica¬tions 473

5.2.1.1 Twisted Nematic Displays 473

5.2.1.2 Nematic Liquid Crystal Materials 477

5.2.1.3 Colour Displays from Twisted Ne¬

matic Liquid Crystals 478

5.2.2 Cholesteric/Chiral Nematic Liquid Crystalsand Their Applications 480

5.2.2.1 Cholesteric Liquid Crystal Displays,

Memory Panels and Electronic Paper 482

5.2.2.2 Temperature Sensing and NoveltyApplications 485

5.2.2.3 Polymeric Cholesteric Liquid Crystalsand Colour 486

5.2.3 Polymer-dispersed Liquid Crystals 488

5.2.4 Side-chain Polymeric Liquid Crystals 489

5.3 Colour from Physical Effects 490

5.3.1 Lustre-and Colour-variable Pigments 491

5.3.1.1 Optical Basis of Pigments Based on

Interference and Diffraction 491

5.3.1.2 Materials, Construction and

Processes 493

5.3.1.3 Applications of Lustre-/Colour-variable Pigments 494

5.3.2 Interferometric Modulator (IMOD)

Technology 495

5.3.3 Iridescent Fibres 497

5.3.4 The Blackest Black - High Absorption and

Low Reflection 497

5.3.5 Colloidal Photonic Crystals 498

5.3.5.1 Chromic Phenomena of Photonic

Crystals and Their Applications 500

5.4 Holography 503

5.4.1 Principles of Holography 503

5.4.1.1 Full-colour Holography 504

5.4.2 Materials Used in Holography 505

5.4.2.1 Photopolymers in Holography 505

5.4.2.2 Rewritable Holographic Media 507

5.4.3 Applications of Holography 508

5.4.3.1 Holographic Data Storage 508

5.4.3.2 Graphic Arts and Design 510

5.4.3.3 Large-scale Displays 510

5.4.3.4 Holographic Optical Elements in

Liquid Crystal Display Systems 511

5.4.3.5 Holographic Optical Elements in

Other Engineering Designs 512

5.5 Laser Diodes 513

5.5.1 Inorganic Semi-conductor Laser Diodes 514

5.5.2 Organic Lasers 515

5.5.2.1 Luminescent Conjugated Polymers 515

5.5.2.2 Single-crystal Organic Materials 517

5.5.2.3 Two-photon Lasing in Dendrimers 518

5.5.2.4 Liquid Crystal Lasers and Laser Dis¬

plays 518

5.5.2.5 Colloidal Photonic Crystal Lasers 520

5.6 Nonlinear Optics 520

5.6.1 Basis of Nonlinear Optics 521

5.6.2 Nonlinear Optical Materials - Second-order or

Quadratic Nonlinearity 522

5.6.2.1 Quadratic NLO Chromophores 522

5.6.2.2 Other Designs for Quadratic NLO

Chromophores 523

5.6.2.3 Quadratic NLO Materials - Poled

Polymers 525

5.6.3 Electro-optic Modulators 528

5.6.4 Wavelength Converters - Harmonic

Generation 530

5.6.4.1 Second Harmonic Imaging

Microscopy 531

5.6.5 Nonlinear Optical Materials - Third-order or

Cubic Nonlinearity 532

5.6.5.1 Multi-photon Absorption 532

5.6.5.2 2PA for High-density Optical Data

Storage 532

5.6.5.3 Reverse Saturable Absorption -

Optical Limiters 534

5.6.5.4 All-optical Signalling 535

5.6.5.5 Cubic NLO Chromophores 536

5.6.6 Photorefractive Polymers 537

5.6.6.1 The Photorefractive Effect 538

5.6.6.2 Amorphous Polymers and

Composites 538

5.6.6.3 Photorefractive Polymer Dispersed

Liquid Crystals 540

5.6.6.4 Applications of Photorefractive

Materials 541

Subject Index 548