Filiations between the Electronic Spectra of C60 and Its Adduct Derivatives: A Rationalization

Considerable similarities are observed between the absorption spectra in the 200–800-nm region of C₆₀ and its n-adduct derivatives (n = 1 − 6), in spite of the fact that two π-electrons are lost for each adduct. The persistence in the adduct derivatives of the main energy and transition strength characteristics of the allowed and forbidden electronic transitions of C₆₀ is rationalized with a relatively simple model. The filial relation between these spectra is discussed on three levels of increasing physical refinement: (i) the electronic states and transitions resulting from a free-electron, spherical shell model of C₆₀; (ii) the effects of an icosahedral potential on such a model; and (iii) the effects of π-electron loss and symmetry lowering due to the addends. The results show that similar, and related, orbital transitions are involved in the absorption spectra in the 200–800-nm region of C₆₀ and its adduct derivatives, albeit mildly affected by changes in molecular symmetry and in the size of the π-conjugation region.