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Novel difluoromethylenated [70]fullerene derivatives, C70(CF2 )n (n=1-3), were obtained by the reaction of C70 with sodium difluorochloroacetate. Two major products, isomeric C70(CF2 ) mono-adducts with [6,6]-open and [6,6]-closed configurations, were isolated and their homofullerene and methanofullerene structures were reliably determined by a variety of methods that included X-ray analysis and high-level spectroscopic techniques. The [6,6]-open isomer of C70(CF2 ) constitutes the first homofullerene example of a non-hetero [70]fullerene derivative in which functionalisation involves the most reactive bond in the polar region of the cage. Voltammetric estimation of the electron affinity of the C70(CF2 ) isomers showed that it is substantially higher for the [6,6]-open isomer (the 70-electron π-conjugated system is retained) than the [6,6]-closed form, the latter being similar to the electron affinity of pristine C70. In situ ESR spectroelectrochemical investigation of the C70(CF2 ) radical anions and DFT calculations of the hyperfine coupling constants provide evidence for the first example of an inter-conversion between the [6,6]-closed and [6,6]-open forms of a cage-modified fullerene driven by an electrochemical one-electron transfer. Thus, [6,6]-closed C70(CF2 ) constitutes an interesting example of a redox-switchable fullerene derivative.

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The thermal and photochemical syntheses of 2,3,9,10-tetrafluoropentacene (F4PEN) from 6,13-etheno bridged precursors were investigated computationally and experimentally. A computational study of the retro-Diels-Alder reaction to give 2,3,9,10-tetrasubstituted pentacenes and pyridazine revealed a linear correlation between barrier height and substituent constant (σ) indicative of an electronic effect that could diminish the yield of electron-poor 2,3,9,10-tetrasubstituted pentacenes in this reaction. The photochemical route from the corresponding bridged α-diketone yields F4PEN, which was characterized photophysically, electrochemically, and structurally. The compound crystallizes in a herringbone motif with quite short intermolecular F-F contacts that are, however, only very weakly bonding according to computations. The electrochemical and photophysical data show that the HOMO-LUMO gap of F4PEN is increased compared to that of PEN. This is due to an increase of the oxidation potential of F4PEN by 0.18 V in combination with an essentially unchanged reduction potential. The radical cation and dication of F4PEN could be generated in oxidizing solvents and characterized by optical spectroscopy and ESR or NMR, respectively. Both charged F4PEN species persist for days in solution.

The boron-nitrogen-boron (BNB) zigzag edged benzo[fg]tetracene is accessible from 4-butyl-2,6-diphenylaniline in four steps in good yields. The two mesityl groups stabilize the boron centers toward nucleophilic attack and result in two enantiomeric forms in the solid state. The title compound has a large optical gap, shows blue fluorescence, and is quite resistant toward oxidation and reduction.

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