MAGNETIC-FIELD EFFECTS UPON PHOTOCHEMISTRY OF BIFUNCTIONAL CHAIN MOLECULES

External magnetic field effects are discussed for three typical examples of photoreactions involving biradical intermediates: photo-induced intramolecular electron transfer in chain molecules D-(CH2)n-A consisting of an electron donor (D) and an acceptor (A), intramolecular hydrogen abstraction in bifunctional species :X-(CH2)n-YH containing a hydrogen donor (YH) and an acceptor (:X in the excited triplet state) and photochemical homolytic ring opening of a cyclic ketone which yields a biradical consisting of an acyl and an alkyl group. There has been progress in the elucidation of reaction mechanisms through the analysis of magnetic field effects on lifetimes of reaction intermediates and product yields in radical reactions involving biradicals. Extremely small interactions such as the Zeeman energy and hyperfine interaction may give rise to a large change in the distribution of photo-products derived from bifunctional chain molecules.