A faux hawk fullerene with PCBM-like properties

Long K. San, Eric V. Bukovsky, Bryon W. Larson, James B. Whitaker, S. H.M. Deng, Nikos Kopidakis, Garry Rumbles, Alexey A. Popov, Yu Sheng Chen, Xue Bin Wang, Olga V. Boltalina, Steven H. Strauss

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Abstract

Reaction of C60, C6F5CF2I, and SnH(n-Bu)3 produced, among other unidentified fullerene derivatives, the two new compounds 1,9-C60(CF2C6F5)H (1) and 1,9-C60(cyclo-CF2(2-C6F4)) (2). The highest isolated yield of 1 was 35% based on C60. Depending on the reaction conditions, the relative amounts of 1 and 2 generated in situ were as high as 85% and 71%, respectively, based on HPLC peak integration and summing over all fullerene species present other than unreacted C60. Compound 1 is thermally stable in 1,2-dichlorobenzene (oDCB) at 160 °C but was rapidly converted to 2 upon addition of Sn2(n-Bu)6 at this temperature. In contrast, complete conversion of 1 to 2 occurred within minutes, or hours, at 25 °C in 90/10 (v/v) PhCN/C6D6 by addition of stoichiometric, or sub-stoichiometric, amounts of proton sponge (PS) or cobaltocene (CoCp2). DFT calculations indicate that when 1 is deprotonated, the anion C60(CF2C6F5)- can undergo facile intramolecular SNAr annulation to form 2 with concomitant loss of F-. To our knowledge this is the first observation of a fullerene-cage carbanion acting as an SNAr nucleophile towards an aromatic C-F bond. The gas-phase electron affinity (EA) of 2 was determined to be 2.805(10) eV by low-temperature PES, higher by 0.12(1) eV than the EA of C60 and higher by 0.18(1) eV than the EA of phenyl-C61-butyric acid methyl ester (PCBM). In contrast, the relative E1/2(0/-) values of 2 and C60, -0.01(1) and 0.00(1) V, respectively, are virtually the same (on this scale, and under the same conditions, the E1/2(0/-) of PCBM is -0.09 V). Time-resolved microwave conductivity charge-carrier yield × mobility values for organic photovoltaic active-layer-type blends of 2 and poly-3-hexylthiophene (P3HT) were comparable to those for equimolar blends of PCBM and P3HT. The structure of solvent-free crystals of 2 was determined by single-crystal X-ray diffraction. The number of nearest-neighbor fullerene-fullerene interactions with centroid⋯centroid (o⋯o) distances of ≤10.34 Å is significantly greater, and the average o⋯o distance is shorter, for 2 (10 nearest neighbors; ave. o⋯o distance = 10.09 Å) than for solvent-free crystals of PCBM (7 nearest neighbors; ave. o⋯o distance = 10.17 Å). Finally, the thermal stability of 2 was found to be far greater than that of PCBM.

Original languageEnglish
Pages (from-to)1801-1815
Number of pages15
JournalChemical Science
Volume6
Issue number3
DOIs
Publication statusPublished - Mar 1 2015

ASJC Scopus subject areas

  • Chemistry(all)

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    San, L. K., Bukovsky, E. V., Larson, B. W., Whitaker, J. B., Deng, S. H. M., Kopidakis, N., Rumbles, G., Popov, A. A., Chen, Y. S., Wang, X. B., Boltalina, O. V., & Strauss, S. H. (2015). A faux hawk fullerene with PCBM-like properties. Chemical Science, 6(3), 1801-1815. https://doi.org/10.1039/c4sc02970d