An electron spin polarization (CIDEP) investigation of the interaction of reactive free radicals with polynitroxyl stable free radicals

Time-resolved electron spin resonance (TR ESR) was employed to investigate the polarized ESR (CIDEP) spectra produced by interaction of mono- and polynitroxyls with reactive free radicals (r[sup [number sign]]) possessing net (single phase) electron polarization. Emissively polarized reactive radicals were produced by photolysis of benzil dimethyl monoketal and absorptively polarized reactive radicals were produced by photolysis of diphenyl (2,4,6-trimethylbenzoyl)phosphine oxide. The stable radicals were mono-, di-, tri-, and tetranitroxyl free radicals processing the 2,2,6,6-tetramethylpiperidine-N-oxyl moiety as a radical unit. The CIDEP spectra obtained under interaction with r[sup [number sign]] and polynitroxyls have the same net emissive (or absorptive) phase as r[sup [number sign]]. The observed CIDEP spectra of dinitroxyls that were obtained in strong exchange (spectroscopic triplets) are interpreted as the superposition of the CIDEP spectrum of the triplet dinitroxyl created by nonreactive polarization transfer from r[sup [number sign]] and the CIDEP spectrum of the adduct of r[sup [number sign]] and one of the nitroxyl moieties. These results provide a novel demonstration of net electron spin polarization transfer (ESPT) in a fast addition reaction of a polarized doublet free radical with diradicals. 22 refs., 4 figs.