Introduction to Photochemistry

Abstract

This chapter summarizes some general concepts in photochemistry, with two aims: to provide an overview of phenomena and empirical rules that will be discussed on theoretical grounds in the next chapters, and to present a language and some physical laws concerning light and its interaction with matter. We shall introduce the main differences between thermal chemistry that takes place in the ground electronic state, and photochemistry, that involves optical excitation. The first overview of elementary photoinduced events will highlight the different ways the excitation energy can be disposed of. We shall distinguish primary and secondary processes and define their quantum yields. Excitation rates will be introduced in connection with the Lambert and Beer law. Some elementary examples of photochemical kinet-ics will be discussed. Much more extended introductions to photochemistry can be found in well-renowned textbooks by Wayne (Principles and Applications of Photo-chemistry.