Intersystem crossing in organic photochemical intermediates
The lifetimes of a number of olefin triplets and triplet biradicals have been determined by nanosecond laser flash spectroscopy. Examples were chosen in an attempt to segregate structural features which affect intersystem crossing rates and thus determine the lifetimes. For olefin triplets, the effects of constraint to planarity, of substitution at the twisted bond for twisted triplets, of deuterium, and of polar substituents are presented. For biradi— cals, the main examples are derived from the Norrish II photoreaction of alkanophenones, and effects of substituent and conforma— tional constraint are discussed. Including Norrish I biradicals of cyclohexanones, examples from zero to four carbons between the termini have been studied.