Some Aspects of the Triplet*

Summary A discussion of certain aspects of triplet state phenomenology which may be of interest to biologists is presented. Particular emphasis is placed on S ‐ T intervals and the interpretation thereof. An attempt is made to relate the size of these intervals to the extent of diradical nature of the triplet state. Spin‐orbital coupling is discussed in a primitive fashion which it is felt leads to much physical insight. External and internal heavy‐atom effects are reviewed and a series of rules relating to the extent to which one might expect a given state of a given compound to be spin‐orbitally coupled are outlined. Finally an attempt is made to analyse objectively some triplet state phenomena and their intervention in biological processes.