Preface

Singlet oxygen, the metastable lowest electronically excited form of the dioxygen molecule, has remained a central research subject since its discovery by Kautsky in 1931. Many reasons account for this. First, this small, nonionic, nonradical form of molecular oxygen meets many of the requirements for a formidable reactive intermediate: its small size allows it to diffuse very easily across exceedingly “crowded” systems such as polymers and cellular structures. Secondly, its unique electronic structure and excess energy make it highly reactive against a large variety of electron-rich substrates. Finally, its relatively long lifetime, from seconds in the gas phase to a few microseconds in water, gives it plenty of time to reach to and react with remote targets.

Three decades have elapsed since a book devoted to singlet oxygen was last published,¹  yet the advances and knowledge gained during this period are so vast and so wide reaching that many felt the time had come for an update. With this spirit in mind, we accepted the challenge posed by the Series Editor Giulio Jori to bring together the community of singlet oxygen researchers and convey their hard-won knowledge into a book that should inspire others entering the field. Giulio did not live to see his book published yet its publication is a tribute to his memory.

The book is divided into five major blocks, which can be read independently. Volume 1 begins with Section I, Fundamentals, giving an overview of the basic facts about singlet oxygen and places it in the context of other reactive oxygen species. Section II, Production of Singlet Oxygen, discusses extensively the ways, materials and techniques used to produce singlet oxygen. We have placed special emphasis on production methods that employ light as energy source as these are most relevant for photonic applications. Section III describes the reactivity of singlet oxygen. The basic reactions are underlined, synthetic applications are beautifully exemplified, and the specific details of singlet oxygen reactivity towards materials and biological components are systematically explored in a series of chapters. To complement this section on reactivity, we encourage our readers to download the review on photo-oxidation of proteins by Michael J. Davies and coworkers.²  This article has been made free to access to accompany this book.

Volume 2 begins with Section IV, which describes the known strategies and techniques to detect and monitor singlet oxygen, ranging from purely spectroscopic methods to the use of chemical traps, spin traps, and fluorescent probes, to the issues pertinent to monitoring the dose of singlet oxygen delivered in photodynamic treatments. Finally, Section V covers the current most significant applications of singlet oxygen science. The reader will find these chapters particularly inspiring as they elegantly demonstrate the importance of singlet oxygen for practical applications in the biosciences and the nanosciences.

We have made every effort to unify nomenclature, abbreviations and symbols throughout the book, as well as to minimize overlap and repetitions between the different chapters. As this is a multiauthor book, avoiding such problems has not always been possible. We beg the reader’s indulgence for it and hope this does not detract from the overall value of the book.

Finally, a few acknowledgements. First and foremost, a big THANK YOU to Giulio Jori for persuading us to undertake the fantastic task of conveying the state-of-the-art in singlet oxygen research into a single book. The journey has been incredibly rewarding as it has allowed us to interact with top scientific colleagues from around the world. Giulio Jori, together with Silvia Braslavsky and Christopher Foote, have been mentors and friends for many years and, as far as singlet oxygen is concerned, the giants who inspired our work and on whose shoulders we still stand. Next, special thanks also to the authors who have contributed to the book. This is your book. We are indebted to you for your insightful science, your commitment and your patience. We wish to extend our gratitude to you reader. This book was designed for you and with you in mind. It is our deepest hope that it helps you attain a sound understanding of the singlet oxygen science and that it inspires you to push its frontiers further away. Last but not least, we would also like to thank our publisher, the Royal Society of Chemistry, and in particular Janet Freshwater, Vicki Marshall, Antonia Pass and Stefan Turner, for the encouragement, advice, and assistance we have received throughout the process of editing this book.

Santi Nonell and Cristina Flors