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 investi gate the polarized ESR (CIDEP) spectra produced by interaction of mono - and polynitroxyls with reactive free radicals (r#) possessing net (s ingle phase) electron polarization. Emissively polarized reactive radi cals were produced by photolysis of benzil dimethyl monoketal and abso rptively polarized reactive radicals were produced by photolysis of di phenyl-2,4,6-trimethylbenzoyl)phosphine oxide. The stable radicals wer e mono-,di-,tri-, and tetranitroxyl free radicals processing the 2,2,6 ,6-tetramethylpiperidine-N-oxyl moiety as a radical unit. The CIDEP sp ectra obtained under interaction with r# and polynitroxyls have the sa me net emissive (or absorptive) phase as r#. The observed CIDEP spectr a of dinitroxyls that were obtained in strong exchange (spectroscopic triplets) are interpreted as the superposition of the CIDEP spectrum o f the triplet dinitroxyl created by nonreactive polarization transfer from r# and the CIDEP spectrum of the adduct of r# and one of the nitr oxyl moieties. These results provide a novel demonstration of net elec tron spin polarization transfer (ESPT) in a fast addition reaction of a polarized doublet free radical with diradicals. The observed CIDEP s pectra involving r# and tri- and tetranitroxyl can also be interpreted in terms of a competition between reactive and nonreactive ESPT but r equire the postulate that nonreactive ESPT between r# and polyradicals of high multiplicity is relatively slow compared to ESPT between r# a nd doublet radicals.