The electrochemical properties of the carbon-bridged fullerene dimers C 121 (I), C 121 (II), C 121 (III), C 131 , and C 141 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-C 60 ) 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 C 60 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 C 60 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.
IntroductionElectrochemical characterization, as one of the most useful tools in the study of electronic properties, has been successfully performed on a lot of fullerenes and their derivatives. The properties, stability, mechanism, and reactivity of fullerene derivatives could be deduced from the experiment. 1-6 Many kinds of fullerene-cage-based derivatives have been synthesized for the purpose of developing electrochemically or optically active systems with different applications, whose basic constructing units are dimer, carbon-bridged dimer, or trimer structures. Their electronic properties are mostly dominated by the electronic interactions between the neighboring fullerene cages of the dimerized units. How the dimerization influences the electronically functional properties is of particular interest for developing as well as understanding the ultimate materials of fullerene derivatives with the desired functions and expected applications such as photovoltaic conversion materials and alloptical switch or optical limiting materials. 7,8 In this work, electrochemical analyses were performed on a series of fullerene dimers, in which the two fullerene cages were
