ИСТИНА

Famed phenyl C61/71 butyric acid methyl ester (PCBM) fullerene derivatives, used commonly as benchmark electron accepting materials for photovoltaic applications, have, as many other products of [2+1] cycloaddition to the fullerene cage, [6,6]-closed structure of the CR2 bridge. On the other hand, there are known [6,6]-open homofullerenes with the notable example of C60CF2 which sports increased electron affinity possibly due to the direct sp2 carbon – CF2 group contact. Unfortunately, alkylation of the C60CF2 dianion, while useful for photovoltaics, leads to the loss of such contact and, as a consequence, lower electron affinity of the resulting compound. [1] Curiously, up to date there are no reported fullerene derivatives with the “in- between” structure of the CR2 bridge: with sp3 carbon on its one end (such as in [6,6]-closed derivatives) and sp2 carbon on the other (such as in [6,6]-open ones). In this work we present one-pot technique which leads from C60 to the C60CF2(R)2 alkylated derivatives with different hybridization of the bridgehead atoms. Properties of such compounds are tunable by the appropriate choice of the R-alkyls which comes in handy for tailoring the material to the desired applications. The influence of having direct sp2 carbon – CF2 group contact on the electronic properties of the material is discussed and the outlook on the perspective applications for the compounds is given. The reported study was funded by RFBR, project number 19-33-90216. [1] Brotsman, V. A., et al. "Alkylated [6, 6]-open difluoromethanofullerenes C60(CF2)R2: Facile synthesis, electrochemical behavior and photovoltaic applications." Electrochimica Acta 219 (2016): 130-142.