Magnetochemical Control of Photoreactions by Multiple Isotope Substitutions

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We have investigated photochemical behavior of bichromophoric chain species containing hydrogen-donor and acceptor moieties. This type of chain molecules undergo intramolecular hydrogen abstraction reactions. Apparent magnetic field and magnetic isotope effects have been observed on photoredox reaction yields of a 4-nitro-1-naphthoxy derivative containing anilino moiety. This is one of few cases where the unimolecular cage reaction predominates in the zero-field and the bimolecular escape process becomes a major reaction pathway on application of external magnetic fields. On the other hand, conspicuous magnetic isotope effects (MIEs) have been detected on lifetimes of biradicals derived from bifunctional chain molecules consisting of aromatic carbonyl compounds and hydrogen-donor groups.Some aspects of bifunctional photochemistry of nitroaryloxy and aromatic carbonyl species are summarized as follows : [1] magnetic field effects on photoredox product yields derived from the bichromophoric parent compounds containing nitro-aromatic moieties,[2] magnetic field and magnetic isotope effects on decay profiles of biradical species,[3] disappearance of heavy carbon magnetic isotope effects in a very high field region.The third phenomenon is explained by taking account of the anisotropic magnetic interactions which contribute to the spin-lattice relaxation. The MIEs are observed when the anisotropic hyperfine interaction is of dominant importance. The MIEs disappear in the presence of very high fields (> 6T) where the anisotropic Zeeman interaction predominates.