Photochemistry is the branch of chemistry which relates to the interactions between matter and photons of visible or ultraviolet light and the subsequent physical and chemical processes which occur from the electronically excited state formed by photon absorption.

The aim of this book is to provide an introduction to the principles and applications of photochemistry and it is generally based on my lectures to second and third - year undergraduate students at Manchester Metropolitan University (MMU).

Chapters 1 and 2 give a general introduction to the concepts of light and matter and to their interaction resulting in electronically excited states. Chapters 3 to 6 relate to processes involving physical deactivation of the electronically excited states. Chapter 7 provides an overview of the chemical properties of excited states including their reaction pathways and the differences between photochemical reactions and the so - called ‘ thermal ’ reactions. Chapters 8 and 9 relate to the photochemical reactions of two of the more interesting groups of organic compounds, namely alkenes and carbonyl compounds. Here the photochemical reactions provide an important extension to the reactions the ground state species. Chapter 10 considers some mechanistic aspects of photochemical reactions and looks at some techniques employed in this fi eld. Chapters 11 and 12 cover areas where outstanding progress has been made in recent years. Chapter 11 considers semiconductor photochemistry whereas in Chapter 12 an introduction to supramolecular photochemistry is presented.