C. Corvaja et al., CIDEP of fullerene C-60 biradical bisadducts by intramolecular triplet-triplet quenching: a novel spin polarization mechanism for biradicals, CHEM P LETT, 330(3-4), 2000, pp. 287-292
[60]fullerene bisadducts containing the C-2 nu-symmetrical 2,2,5,5-tetramet
hylpyrroiidine-1-oxyl moiety have been synthesized. Their EPR spectrum is t
ypical of nitroxide biradicals with electron exchange interaction J of the
same order of the nitrogen hyperfine coupling. From the EPR spectrum the ab
solute value of J was obtained, while the sign was measured by ENDOR. When
the derivatives are photoexcited strong spin polarization is observed with
A/E/A/E or E/A/E/A patterns, according to a positive or a negative sign of
J. This behavior is accounted for by an intramolecular triplet-triplet inte
raction. The analogy with the polarization of transient spin correlated rad
ical pairs is pointed out. (C) 2000 Elsevier Science B.V. All rights reserv
ed.