ИСТИНА

Design of novel materials with desired molecular structure and electronic properties are the key for fabrication of effective organic electronic devices. Fullerene derivatives are prospective materials for such application due to their electronic conductivity and possibility of fine tuning of electronic band structure via specific arrangement of addends and insertion of various molecular fragments. For example, we showed that difluorocarbene addition to C60 results in homofullerene C60(CF2) with enhanced electron affinity due to unprecedented annulenic structure. Recently we synthesized two valence isomers of C70(CF2) where CF2 moieties have cyclopropanated and annulenic configurations (so-called "closed" and "open" isomers). The valence isomers of C70(CF2) demonstrates different electrochemical behavior and electron affinities. Furthermore, reversible electron-driven interconversion between cyclopropanated and annulenic configurations was experimentally proved by means of in situ ESR spectroelectrochemical studies. These results stimulated us to performed studies of fullerenes derivatives where such interconversion provokes significant changes in the π-conjugated system and, therefore, structure of boundary molecular orbitals. Novel methylene and difluoromethylene derivatives of poly(trifluoromethyl)fullerene Сs-C70(CF3)8 were obtained by the cycloaddition reaction of diazomethane and carbene :CF2. High selectivity of the fullerene cage methylenation is predetermined by orienting effect of CF3 groups with near-equatorial addition pattern. Two products, Сs-C70(CF3)8[CF2] with [5,6]-open configuration (rC–C=2.09 Å) and Сs-C70(CF3)8[CH2] with [5,6]-closed configuration (rC–C=1.69 Å), were isolated and their structures were reliably determined by single crystal X-ray analysis and NMR spectroscopy (Fig. 1). The unexpected effects of the attachment of CX2, X=F and H, moiety to fullerene cage on its structural and electronic features are interpreted by means of quantum chemical calculation performed at the DFT level of the theory.