Chromic Phenomena The Technological Applications of Colour Chemistry Peter Bamfield Consultant ISBN 0-8404-474-4 A catalogue record for this book is available from the British Library © The Royal Society of Chemistry 2001 All rights reserved. Apart from any fair dealing for the purpose of research or private study, or criticism or review as permitted under the terms of the UK Copyright, Designs and Patents Act, 1988, this publi- cation may not be reproduced, stored or transmitted, in any form or by any means, without the prior permission in writing of The Royal Society of Chemistry, or in the case of reprographic reproduction only in accordance with the terms of the licences issued by the Copyright Licensing Agency in the UK, or in accordance with the terms of the licences issued by the appropriate Reproduction Rights Organization outside the UK. Enquiries concerning repro- duction outside the terms stated here should be sent to The Royal Society of Chemistry at the address printed on this page. Published by The Royal Society of Chemistry, Thomas Graham House, Science Park, Milton Road, Cambridge CB4 0WF, UK Registered Charity Number 207890 For further information see our web site at www.rsc.org Typeset in Great Britain by Wyvern 21 Ltd, Bristol Printed by MPG Books Ltd, Bodmin, Cornwall, UK Preface The aim of this book is to provide an overview of the many applications that colour chemistry, in its widest sense, has found in the last couple of decades. Not only have there been developments in the traditional areas of colorants for textiles, paints and inks but also in an exciting variety of newer technologies. Several of these are at the cutting edge of research, such as photodynamic therapy, electroluminescent displays, artificial photosynthesis, holographic data storage and photonics, and any report on the current position can only be interim. Most of the newer technologies are multi- disciplinary, where the active collaboration of chemists with physicists, biologists, biochemists, materials scientists, electronics engineers etc. is essential if any progress is to be made. Covering as it does a very wide field, this book will provide an entry point for both new researchers and established ones who wish to broaden their horizons and accept the challenge of finding new applications for colour chemistry. During my more than four decades involvement in the colorants industry I have had many stimulating discussions and collaborations with innumerable colleagues to whom I am indebted. I would particularly like to mention Peter Austin, Gerald Booth, Peter Gregory, Paul Gordon, Colin Greenhalgh, Nigel Hughes, Mike Hutchings, Brian Parton, Duncan Phillips, Ray Price, Peter Quan, Peter Tasker, Hunter Renfrew, Dennis Ridyard, John Schofield and John Taylor from my ICI/Zeneca days. Finally, but most of all, I wish to thank my wife Mary for her unstinting support during the books gestation period and particularly whilst I was producing the manuscript. Peter Bamfield v Contents Introduction 1 Chapter 1 Phenomena Involving a Reversible Colour Change 7 1.1 Introduction 7 1.2 Photochromism 7 1.2.1 Main Chemical Classes 8 1.2.2 Spirobenzopyrans 9 1.2.2.1 Synthesis of Spiroindolinobenzopyrans 9 1.2.2.2 Spectral Properties of Spiroindolinobenzopyrans and Analogues 10 1.2.3 Spironaphthoxazines 11 1.2.3.1 Synthesis of Spiroindolinonaphthoxazines and Analogues 11 1.2.3.2 Spectral and Physical Properties of Spiroindolinonaphthoxazines 13 1.2.4 Benzo and Naphthopyrans (Chromenes) 15 1.2.4.1 Synthesis of Benzopyrans and Naphthopyrans 16 1.2.4.2 Spectral and Physical Properties of Diarylnaphthopyrans 17 1.2.5 Fulgides 20 1.2.5.1 Synthesis of Fulgides and Derivatives 21 1.2.5.2 Spectral and Physical Properties of Fulgides and Derivatives 22 1.2.6 Diarylethenes 23 1.2.6.1 Synthesis of Diheteroarylethenes 24 1.2.6.2 Spectral and Physical Properties of Dithiophenylethenes 25 1.2.7 Miscellaneous Photochromic Systems 26 1.2.8 Applications of Photochromic Materials 28 1.2.8.1 Applications in Ophthalmics 29 1.2.8.2 Novelty Printing and Textile Applications 30 1.2.8.3 Optical Memories and Switches 30 1.2.8.4 Other Optical Applications 32 1.2.8.5 Biological Applications 33 1.3 Thermochromism 33 1.3.1 Inorganic and Organometallic Materials 34 1.3.2 Reversible Intrinsically Thermochromic Organic Systems 34 1.3.2.1 Molecular Rearrangements 34 1.3.2.2 Stereoisomerism 36 vii viii Contents 1.3.2.3 Macromolecular Systems 37 1.3.3 Reversible Indirect Thermochromic Systems 37 1.3.4 Applications of Thermochromic Materials 38 1.3.4.1 Composite Thermochromic Pigments 38 1.3.4.2 Chromogenic Thermotropic Gels 40 1.4 Ionochromism 41 1.4.1 Ionochromic Compounds 41 1.4.1.1 Phthalides 41 1.4.1.2 Leucotriarylmethanes 45 1.4.1.3 Fluorans 45 1.4.1.4 Azo and Styryl Dyes 46 1.4.1.5 Chelates and Crown Ethers 46 1.4.2 Applications of Ionochromism 48 1.4.2.1 Analytical Chemistry 48 1.4.2.2 Carbonless Copying Paper 50 1.4.2.3 Direct Thermal Printing 50 1.4.2.4 Visualisation of Printing Plates 52 1.4.2.5 In Flower Coloration 52 1.5 Electrochromism 53 1.5.1 Electrochromic Cells 53 1.5.2 Electrochrome Types 54 1.5.2.1 Solution Electrochromes 55 1.5.2.2 Solution–Solid Electrochromes 55 1.5.2.3 Solid Electrochromes 55 1.5.3 Electrochromic Chemicals 55 1.5.3.1 Inorganic Oxides 55 1.5.3.2 Prussian Blue 56 1.5.3.3 Metal Phthalocyanines 57 1.5.3.4 Viologens (4,4′-bipyridylium salts) 58 1.5.3.5 Polymeric Electrochromes 58 1.5.3.6 Other Organic Electrochromes 61 1.5.4 Applications of Electrochromism 61 1.5.4.1 Rear-view Mirrors 61 1.5.4.2 Smart Windows 62 1.5.4.3 Displays 64 1.6 Solvatochromism 66 1.6.1 Solvent Polarity and Solvatochromic Shifts 66 1.6.2 Applications of Solvatochromism 67 1.6.2.1 Analysis of Oils 67 1.6.2.2 Polymer Probes and Sensors 68 1.6.2.3 Biological Probes 68 1.7 Miscellaneous Chromisms 69 1.7.1 Piezo and Tribochromisms 69 1.7.2 Gasochromism 70 1.7.3 Vapochromism 70 1.7.4 Chronochromism 70 Contents ix 1.8 References 70 Chapter 2 Phenomena Involving the Absorption and Reflectance of Light 75 2.1 Introduction 75 2.2 Some Elements of Colour Physics Relating to Colorants 76 2.2.1 Additive Colour Mixing 76 2.2.2 Subtractive Colour Mixing 77 2.2.3 The CIE System 78 2.3 Classical Organic Dyes 80 2.3.1 Structural Classes 81 2.3.1.1 Azo Dyestuffs 81 2.3.1.2 Cyclic and Polycyclic Quinones 91 2.3.1.3 Azines, Oxazines and Thiazines 95 2.3.1.4 Methines 96 2.3.1.5 Triaryl Carbonium Dyes 98 2.3.1.6 Phthalocyanines 98 2.3.2 Application Processes 99 2.3.2.1 The Dyeing and Printing of Textile Fibres 99 2.3.2.2 Paper 108 2.3.2.3 Leather 108 2.3.2.4 Food 108 2.3.2.5 Hair Coloration 110 2.3.2.6 Biological Stains 111 2.4 Pigments 112 2.4.1 Organic Pigments 113 2.4.1.1 Azo Pigments 114 2.4.1.2 Metal Complexes 117 2.4.1.3 Isoindolinone Pigments 118 2.4.1.4 Phthalocyanines 119 2.4.1.5 Quinacridones 120 2.4.1.6 Perylenes and Perinones 121 2.4.1.7 Polycyclic Quinones 123 2.4.1.8 Diketo-pyrrolopyrroles 124 2.4.1.9 Triaryl Carboniums 124 2.4.2 Inorganic Pigments 124 2.4.2.1 Iron Oxides 125 2.4.2.2 Chromium Oxide 126 2.4.2.3 Mixed Oxides 126 2.4.2.4 Alternatives to Cadmium Pigments 127 2.4.2.5 Chromate Pigments 127 2.4.2.6 Ultramarine Pigments 127 2.4.2.7 Iron Blue Pigments 127 2.4.3 Special Effect Pigments 128 2.4.4 Applications of Coloured Pigments 128 2.4.4.1 Dispersion of Pigments 129 x Contents 2.4.4.2 Printing Inks 129 2.4.4.3 Paints and Coatings 130 2.4.4.4 Plastics 130 2.4.4.5 Construction Materials and Ceramics 131 2.5 Solvent Dyes 131 2.6 Photographic Colour Chemicals 132 2.6.1 Colour Photographic Process 132 2.6.2 Colour Films and Papers 133 2.6.2.1 Colour Reversal Film 133 2.6.2.2 Colour Negative Film 133 2.6.2.3 Colour Papers and Prints 135 2.6.2.4 Instant Colour Photographic Films and Paper 135 2.6.3 The Colour Forming Chemicals in Photography 135 2.6.3.1 Colour Developers 136 2.6.3.2 Colour Couplers and Derived Dyes 136 2.6.3.3 Diffusion Couplers 140 2.7 Digital Printing 140 2.7.1 Ink Jet Printing 142 2.7.1.1 Continuous Ink Jet 143 2.7.1.2 Drop-on-demand Ink Jet 143 2.7.1.3 Colorants in Ink Jet Printers 145 2.7.1.4 Commercial Applications of Ink Jet Technology 147 2.7.2 Electrophotography 147 2.7.2.1 Materials for Electrophotography 149 2.7.2.2 Commercial Applications of Electrophotography 151 2.8 References 152 Chapter 3 Phenomena Involving Absorption of Energy and Emission of Light 155 3.1 Introduction 155 3.2 Luminescent Pigments 157 3.2.1 Inorganic Phosphors 158 3.2.1.1 Sulfides and Oxysulfides 158 3.2.1.2 Oxygen-dominant Phosphors 159 3.2.2 Synthesis and Formulation of Inorganic Phosphors 159 3.2.3 Up-converters 160 3.2.4 Applications of Inorganic Phosphors 161 3.2.4.1 Phosphorescent Pigments 161 3.3 Cathodoluminescence 163 3.4 High Energy Photoluminescence 166 3.4.1 Lighting 166 3.4.2 Plasma Displays 167 3.5 Fluorescence 169 3.5.1 Fluorescent Chromophores 170 3.5.1.1 Coumarins 170 3.5.1.2 Naphthalimides 172 Contents xi 3.5.1.3 Perylenes 173 3.5.1.4 Benzanthrones, Anthraquinones, Benzoxanthones and Benzthioxanthones 174 3.5.1.5 Xanthenes, Acridines and Oxazines 176 3.5.1.6 Hydrocarbons 179 3.5.1.7 Methines, Hemicyanines and Cyanines 179 3.5.1.8 Dipyrromethines 181 3.5.1.9 Miscellaneous Chromophores 181 3.5.2 Applications as Fluorescent Dyes and Pigments 182 3.5.2.1 Fluorescent Dyes in Textile Applications 183 3.5.2.2 Daylight Fluorescent Pigments 183 3.5.2.3 Other Applications 184 3.5.3 Dye Lasers 184 3.5.3.1 Types of Dye Lasers 185 3.5.3.2 Mechanism of Dye Lasers 186 3.5.3.3 Laser Dyes 186 3.5.3.4 Applications of Dye Lasers 186 3.5.4 Fluorescent Brighteners 187 3.5.4.1 Stilbene Based