ELECTROCHEMICAL MONITORING OF VALENCE-BOND ISOMERS INTERCONVERSION IN BIPYRIDYL-C-61(PERPENDICULAR-TO) ANIONS

Electrochemical, quantum chemical, and spectroscopic techniques are used to study the dynamics of the reduction of bpy-C-61. A thorough investigation of the temperature and scan rate dependence of the cyclic voltammetry peaks coupled with numerical simulations clearly reveals that the trianion and the tetraanion undergo two chemical reactions according to the same parallel ECE mechanism. Quantum chemical calculations show that three isomers are quasi equienergetic in the charged states and support the hypothesis that triply and quadruply reduced bpy-C-61 undergoes facile conversion among three of its structural isomers, i.e., [5,6]-closed bpy-C-61, [5,6]-open bpy-C-61, and [6,6]-closed bpy-C-61. Substituent and/or solvent effects may effectively reverse the roles of [5,6]-closed bpy-C-61 and [6,6]-closed bpy-C-61. As for [5,6]-closed isomer, it is the first time that its existence is proposed on the basis of the observation of a redox process. The six reduction peaks of C-60 have been observed for the first time in a pure solvent (THF, -60 degrees C), and the cyclic voltammetry peaks of the fullerene moiety and the bpy fragment have been assigned.