Facile Separation, Spectroscopic Identification, and Electrochemical Properties of Higher Trifluoromethylated Derivatives of [70]Fullerene

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.

Electrochemically Induced Dimerization of p9mp-C70(CF3)12 Trifluoromethylated Fullerene

“…The electronic properties of the trifluoromethylated fullerenes are governed more by the exact addition pattern rather than by the sheer number of the electron-withdrawing CF 3 addends. Apparent correlations between the addition pattern and various electronic characteristics have been demonstrated in some previous works. ,, A particularly vivid example is the 0.5 V difference in the first reduction potential between two of the isomers of C 70 (CF 3 ) 20 …”

“…Metastable ions of trifluoromethylfullerenes are observed in the reflector ToF mass spectra because of delayed monomolecular decay of respective molecular ions in the field-free region . It is worth noting that C 70 (CF 3 ) 12 -III shows appreciable fragmentation under the MALDI conditions, in contrast to the previously known isomers I and II, even though it does not comprise the skew pentagonal pyramid addition pattern that is normally responsible for the high fragmentation rate of the negative ions …”

“…Trifluoromethylated fullerenes are a particularly diverse and extensively studied family of fullerene derivatives. − Thus, more than 40 individual compounds of C 70 (CF 3 ) n have been reported to date with n ranging from 2 to 20. ,, Most of those molecules combine high thermal stability and fair solubility in common organic solvents, which allows for fabrication of, e.g., thin-film optoelectronic devices via established gas- and liquid-phase protocols. The electronic properties of the trifluoromethylated fullerenes are governed more by the exact addition pattern rather than by the sheer number of the electron-withdrawing CF 3 addends.…”

“…In our recent work, we have reported an improved HPLC separation protocol that provides some previously inaccessible C 70 (CF 3 ) n isomers with n = 12–20. Most of the compounds have been structurally characterized by means of single-crystal X-ray diffraction.…”

Chlorination‐Promoted Cage Transformation of IPR C92 Discovered via Trifluoromethylation under Formation of Non‐classical C92(NC)(CF3)22

“…The formation of an isolated C=C bond can be responsible for a small positive effect in C 92 (38)(CF 3 ) 14 , whereas simple additions of two CF 3 groups in C 92 (38)(CF 3 ) 16/18 have pronounced negative effects due to the increased numbers of attached addends. The E rel /1CF 3 values for n= 20 can be calculated for the known CF 3 derivatives of C 70 , C 84 (22), and C 94 (61): −10.1, −12.1, and −5.1 kJ mol −1 , respectively. Therefore, the expected E rel /1CF 3 value for a fullerene derivative with 22 attached CF 3 groups is at least below −10 kJ mol −1 .…”