SENSITIZED PHOTOOXYGENATION REACTIONS AND THE ROLE OF SINGLET OXYGEN†,‡

Abstract— In this paper we discuss various theoretical and experimental aspects of the role of singlet oxygen in sensitized photooxygenation reactions. New spectroscopic observations on the photosensitized production of singlet oxygen molecules are presented. The various factors which control the generation and reactions of singlet oxygen molecules are considered in detail. A relatively simple theoretical procedure is developed to predict the relative reactivities of ¹σ, ¹δ and ³σ oxygen toward various organic acceptors, and is used to discuss the chemical and photochemical properties of some of the oxygenation products. Finally, the properties of dioxetanes are examined in connection with the role which they may play in chemi- and bioluminescence. While we have said rather little about photodynamic reactions per se , the results presented in this paper strongly support the suggestion that many of the observed photodynamic effects could be due to reactions of singlet oxygen. Clearly a careful reexamination of various photodynamic effects at the molecular level to establish whether or not reactions of singlet oxygen are involved is now in order.