Density Functional Theory Study on the Decay of Fullerenyl Radicals RC60•, ROC60•, and ROOC60• (R = tert-Butyl and Cumyl) and Polarizability of the Formed Fullerene Dimers

Currently, there are no comparative studies on the possible routes of decay of fullerenyl radicals. Such information is required for development of new synthetic approaches to the fullerene derivatives, obtained via radical reactions, and understanding mechanisms of oxidative destruction of fullerene-containing materials. In the present work, we have performed a theoretical study on the possible reactions of the selected fullerenyl radicals, generated in the well-known experimental systems. We consider three main routes for the radical decay: formation of fullerene bisadducts via XC60 center dot + X-center dot reactions, dimerization of XC60 center dot, and their interaction with molecular oxygen. The calculated heat effects explain the experimental regularities of fullerene radical reactions (e.g., the reversibility of the dimerization and low reactivity of fullerenyls toward molecular oxygen). We have found that the heat effects are maximal for the dimerization of ROOC60 center dot, so the interaction of C-60 with peroxy radicals may provide more effective synthetic routes to the single-bonded C-60 dimers compared to the known ones. Moreover, the exothermicity of ROO center dot addition to C-60 is increased during the subsequent addition that allows reconsidering the reasons underlying C-60 antioxidant activity. Additionally, polarizability and its nonadditivity of fullerene dimers XC60-C60X have been found. Guided by the calculated polarizabilities, we assume a new bistable system fullerenyl <-> dimer for molecular machinery. Depending on the conditions, such a system can exist in two states differing by their response to external electric fields.