Isomeric and structural impacts on electron acceptability of carbon cages in atom-bridged fullerene dimers

The electrochemical properties of the carbon-bridged fullerene dimers C₁₂₁(I), C₁₂₁(II), C₁₂₁(III), C₁₃₁, and C₁₄₁ were characterized systematically for the first time in this study. Cyclic voltammogram and differential pulse voltammogram analyses revealed that they first underwent three reversible fullerene-unit-based reduction processes where each of the two carbon cages accepted one electron in each step and then possessed a different deep reduction sequence from the fourth to sixth reduction potentials of the fullerene cages. The electronic interactions between cages in the atom-bridged dimers (e.g., C ₆₀-C-C₆₀) were found to be different from those of dimers in which two cages were connected directly. Comparison studies of the redox properties of the five dimers revealed that the C₆₀ dimerization via [5.6]-[6.6] connection influenced the cage electron acceptability much more than that of [5.6]-[5.6] or [6.6]-[6.6] connections and the dimerization with C ₇₀ cages influenced the reduction potentials of dimerized products more potently than that with C₆₀ cages. Further results from controlled potential electrolysis, high-performance liquid chromatography, matrix-assisted laser desorption and ionization time-of-flight mass spectrometry, ultraviolet absorption spectral analyses demonstrated the reduction processes and a dissociation of the dimers based on reductions. The theoretical understanding of the experiments was investigated by using time-dependent density functional calculations for the ionic states of C ₁₂₁(I, II, III)^n- with n = 0, 1, 2, 3, or 4.