Absorption spectra of the mono-adduct and the eight bis-addict regioisomers of pyrrolidine derivatives of C60

Absorption spectra of the pyrrolidine N-mTEG (mTEG¼CH2CH2OCH2CH2OCH2CH2OCH3) mono-adduct and eight bis-adducts of C60 were studied in the 230–800 nm spectral range. The five-membered ring adducts contain an apex nitrogen atom. A theoretical discussion in terms of the effective electronic structures and transitions of these species shows that a filiation between spectra of C60, and its pyrrolidine mono- and bis-adduct derivatives can be expected and rationalised. Allowed transitions in the ultraviolet are related to fullerene core electronic transitions and are observed to be little affected in energy and in transition strength by the mono-adduct, apart from band splitting or broadening associated with the lowered molecular symmetry with respect to C60, whereas in the visible region, the transitions related to C60 forbidden transitions are significantly modified by the adduct. The bis-adducts have similar general spectral behaviour to that of the mono-adduct, with differences that reflect the relative position of the two addends but are found to be not dependent on membership of any of the three formal symmetry groups into which the bis-adducts can be classified. The second pyrrolidine adduct reinforces the perturbation of the forbidden and, to a lesser extent, the allowed transitions of the fullerene core. From a comparison with the spectra of C60[C(COOEt)2] and its bisadducts, it was concluded that the N atom in the pyrrolidine five-membered ring adduct is a less efficient blocker of through-bond and/or through-space communication than the sp3 carbon atom in Bingel–Hirsch methanofullerenes.