Effects of lowering symmetry on the ESR spectra of radical anions of fullerene derivatives and the reduction potentials

Shunichi Fukuzumi, Hisahiro Mori, Tomoyoshi Suenobu, Hiroshi Imahori, Xiang Gao, Karl M. Kadish

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Radical anions of dibenzyl adducts of C60, 1,4-(C6H5CH2)2C60 ̇- and 1, 2-(C6H5CH2)2C60 ̇-, give ESR spectra which have larger g values (2.0004 and 2.0001, respectively) and much smaller line widths (ΔHmst = 2.5 and 3.3 G, respectively, at 213 K) than the g value (1.9984) and the ΔHmsl value (30.9 G at 213 K) of C60̇-. An even smaller ΔHmsl value (0.17 G) and a larger g value (2.0011) are observed for the tetrabenzyl Ceo adduct radical anion, 1, 4, 10, 24-(C6H5CH2)4C60 ̇- and this is ascribed to a large splitting of the degenerate t1u Orbitals caused by introduction of four benzyl groups to C60. In this case, a hyperfine structure, due to two nonequivalent protons of only one benzyl group (aH1 = 0.31 G, aH2 = 0.11 G), is observed and this is consistent with the predicted localized spin density at the C2 position next to the C1 carbon to which a benzyl group is attached. The radical anions of the mono- and bisadducts formed in the Diels-Alder cycloaddition reaction of C60 with 9, 10-dimethylanthracene show ESR signals at different g values (2.0003 for the monoadduct and 2.0009 for the bisadduct). The relationship between lower symmetry and the ESR spectra of radical anions of various CM derivatives is discussed in terms of the g values and the line widths. The energy gap (δ) between the singly occupied orbital and the two other Orbitals which had a tiu symmetry prior to introduction of addends to C60 is derived from differences in the g values of various C60̇- derivatives from the free spin value (2.0023). A linear correlation is shown to exist between log Affmsi and -o. The ovalues are also obtained from Arrhenius plots of In ΔHmsl vs T-1 and they agree well with the values derived from the g values and the reduction potentials.

Original languageEnglish
Pages (from-to)10688-10694
Number of pages7
JournalJournal of Physical Chemistry A
Issue number46
StatePublished - 23 Nov 2000


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