Magnetic Field Effects on Excited-State Oxygen-Organic Molecule Interactions

摘要

The effects of an applied magnetic field (<22 KG) on (1) the lifetime of singletoxygen (1 sup delta g O2) and (2) the quenching of triplet chrysene by ground-state oxygen (3 sup sigma g (-) O2) were examined in liquid solvents and solid organic polymers. Each process involves a 'spin-forbidden' transition between states of an oxygen-organic molecule (M) encounter pair. Under certain conditions, the 1 sup delta g O2), and 3 chrysene deactivation rates decreased with an increase in the magnetic field strength. The data are consistent with a model in which the M-(O2) charge-transfer state (M(+) O2(-)) imparts geminate radical ion character into lower lying states of the M-(O2) encounter pair through configuration interaction. Magnetic field effects appear to derive from changes in the rate of singlet-triplet spin evolution in M-(O2) states with radical ion pair character and are most pronounced (1) in solvents where the charge-transfer state is more stable, (2) when M and O2 are held in close proximity for a longer period of time, and (3) when the rate of singlet-triplet spin evolution is much slower than dissociation of the excited-state M-(O2) encounter pair to regenerate solvated reactants. Furthermore, the observation of a solvent hydrogen/deuterium magnetic isotope effect on the 1 sup delta g O2 lifetime is consistent with a mechanism in which hyperfine interactions influence the rate of electron spin evolution. Where magnetic field effects were observed, the data indicate that singlet-state-triplet-state mixing becomes less probable at higher field strengths.