Foreword

It is a pleasure to commend this book Singlet Oxygen. The Editors are certainly to be congratulated on persuading so many international experts in this area to contribute chapters on a great variety of topic and of a high scientific standard. I am sure this state-of-the-art volume will become an indispensible reference source for many years to come for those interested in, and researching, singlet oxygen.

In 1957 when I started research on electronic energy transfer in solution as a research student with Professor George Porter, later to become Sir George, then Lord Porter and Nobel Laureate, lasers had not been invented. In order to detect triplet states, the lowest excited state of most molecules, exciting with flashlamps of microsecond duration, oxygen had to be rigorously removed from all solutions, since oxygen was known to efficiently quench electronically excited states. Although Kautsky and de Bruijn¹  had proposed quenching produced singlet oxygen as a reactive intermediate in dye-sensitized photo-oxygenations as early as 1931 it was not until 1964 that this became generally accepted when Foote and Wexler²  and Corey and Taylor³  demonstrated that the oxygenation product distribution for several substrates from chemically generated (using H₂O₂/NaOCl) and from radio-frequency generated singlet oxygen, was the same as in sensitized photo-oxygenation of these same substrates. In 1968, Foote and Denny⁴  showed that the sensitized photo-oxygenation of 2-methylpent-2-ene is reduced markedly in the presence of beta-carotene and by assuming energy transfer from singlet oxygen to beta-carotene was diffusion controlled with a rate constant of 3 × 10¹⁰ dm³ mol^–1 s^–1 they estimated that the lifetime of singlet oxygen was about 10 µs in benzene solution. This value was in striking agreement with the value of 12.5 µs obtained three years later from time-resolved measurements in my laboratory⁵  using a laser flash photolysis system.

By 1981 James Brummer and I⁶  in a critical comprehensive compilation of the literature were able to report lifetimes in 50 different solvents and second-order rate constants for deactivation and chemical reaction of singlet oxygen with 690 different compounds. The update⁷  in 1995 (20 years ago) reported lifetimes in 145 solvents and solvent mixtures and rate constants for chemical reaction and deactivation of singlet oxygen with 1900 different compounds. This demonstrates the ever increasing interest by scientists in the properties and reactions of singlet oxygen.

As pointed out in the preface it is 30 years since a book was published on singlet oxygen. However, as the many references at the end of the chapters in this book demonstrate research concerning singlet oxygen continues to grow. It is not surprising therefore that the Series Editor Giulio Jori should have encouraged the editors to produce a book on singlet oxygen, a research area in which he made many important contributions. It is a great pity he did not live long enough to see the book in print.

Francis Wilkinson

Norwich, UK

[email protected]