No abstract

We survey the structure and electronic properties of the family of higher trifluoromethylated C (CF ) molecules with n=14, 16, 18, and 20. Twenty-two available compounds, of which thirteen are newly obtained and characterized, demonstrate the broad diversity of π-system topologies, which enabled us to study the interplay between the CF addition pattern and the electronic properties. UV/Vis spectroscopic and cyclic voltammetric studies demonstrate the importance of the exact addition pattern rather than the plain number of addends. Of particular interest is the skew pentagonal pyramid (SPP) addition pattern, which enables formation of closed-shell cyclopentadienyl anions C (CF ) through CF detachment upon electron transfer. A detailed study of the process is presented for a SPP-C (CF ) where potentiostatic electrolysis at the second reduction potential gives C (CF ) oxidizable to a persistent C (CF ) radical. Together with the literature data for the lower C (CF ) compounds with n=2-12, the present results show good correlation between the experimental boundary level positions and the DFT predictions. The compounds turn out to be electron acceptor molecular semiconductors with experimental LUMO energies and HOMO-LUMO gaps within the ranges of -4.3 to -3.7 eV and 1.6 to 3.3 eV, respectively, depending on the shape of the conjugated fragments. The HOMO levels fall within the range of -5.6 to -6.9 eV and show linear correlation with the number of addends.

Four CF 3 derivatives of C 78 , C 78 (2)(CF 3 ) 10/12 and C 78 (3)(CF 3 ) 12/14 , have been isolated via HPLC from the products of high-temperature trifluoromethylation of a C 76 -C 96 fullerene mixture or a C 78 fraction. Their molecular structures were determined by single crystal X-ray crystallography using synchrotron radiation. The addition patterns of the new compounds are compared with each other and with the previously known C 78 (2)(CF 3 ) 10 and C 78 (3)(CF 3 ) 12 .

High-temperature trifluoromethylation of fullerene C78 followed by HPLC separation of C78 (CF3)n derivatives resulted in the isolation and X-ray structural characterization of 15 compounds, that is, two C78(1)(CF3)10, three C78 (1)(CF3)12, four C78 (1)(CF3)14, and five C78 (1)(CF3)16 isomers as well as one isomer of C78(1)(CF3)18. The addition patterns of the C78(1)(CF3)n molecules are discussed in terms of trifluoromethylation pathways and relative formation energies.

We report a comprehensive study of a novel isomer of C 70 (CF 3 ) 12 , p 9 mp-C 70 (CF 3 ) 12 , whose electrochemical behavior differs from most of the other trifluoromethylated fullerenes. The addition pattern of p 9 mp-C 70 (CF 3 ) 12 is established by means of 19 F− 19 F COSY NMR spectroscopy and DFT calculations. Like p 7 mp-C 70 (CF 3 ) 10 , the new isomer p 9 mp-C 70 (CF 3 ) 12 undergoes dimerization to the [C 70 (CF 3 ) 12 ] 2 2− upon single-electron reduction. The electrochemical observations are supported by the DFT calculations of dimerization energy and the temperature dependence of the CW X-band EPR spectroscopy data. Experimentally determined dimerization energies of p 9 mp-C 70 (CF 3 ) 12 −• and p 7 mp-C 70 (CF 3 ) 10 −• in solution are ca −8 and −26 kJ mol −1 , respectively, in good correspondence with DFT data.