Saturation versus inductive effects: the electrochemistry of the C70Ph2n (n = 1–5) series

Abstract

Several arylfullerenes, C 70 Ph 2n (n = 1-5), are characterised. Their electrochemical properties, investigated by cyclic voltammetry, are the result of a competition between the electron-withdrawing effect exerted by the phenyl groups and the destabilization of redox orbitals deriving from the saturation of double bonds. C 70 Ph 2 is easier to reduce than C 70 , a feature possibly shared with C 70 Ph 4 that makes these derivatives of C 70 amongst the best electron acceptor molecules so far discovered. In the following derivatives, destabilization prevails, and reductions become increasingly more cathodic along the series. NMR spectroscopy is used to investigate C 70 Ph 2n (n = 1-3). Finally, calculation of the LUMO energies supports the earlier reduction of C 70 Ph 2 and calculations also indicate the layering of the injected charges, in the multiply-reduced species, over concentric shells.

Synthesis, Characterization, and Theoretical Study of Stable Isomers of C70(CF3)n (n = 2, 4, 6, 8, 10)

“…An isomer of C 70 Ph 6 was the subject of several papers in 2000 and 2001. [27,28,39] The reported NMR spectroscopic data demonstrated that the phenyl groups were arranged to give three symmetry-related pairs. For reasons that are not clear, the authors considered only the C s -p 5 -C 70 X 6 and C s -p 2 ,p 2 -C 70 X 6 addition patterns as possibilities for their compound.…”

“…For example, in one paper the mismatch between the number of sp 2 13 C resonances for C 70 Ph 6 and the number expected for the "most likely" C s -p 5 structure was explained away as "probably due to signal coincidence" despite the fact that the C 2 -p 5 structure would naturally give rise to fewer signals. [28] Furthermore, in another paper the small S 0 -S 1 energy gap predicted [27] for C s -p 5 -C 70 Ph 6 required that its fluorescence at 728 nm was due to a highly unusual radiative relaxation from an S 2 state instead of from the S 1 state. [27] Our DFT HOMO-LUMO gaps for C s -p 5 -and C 2 -p 5 -C 70 Ph 6 are 0.49 and 1.41 eV, respectively, so once again the reported data are better explained by assuming that the isomer of C 70 Ph 6 that has been isolated and studied in the past [27,28,39] is in fact the C 2 -p 5 isomer.…”

“…[28] Furthermore, in another paper the small S 0 -S 1 energy gap predicted [27] for C s -p 5 -C 70 Ph 6 required that its fluorescence at 728 nm was due to a highly unusual radiative relaxation from an S 2 state instead of from the S 1 state. [27] Our DFT HOMO-LUMO gaps for C s -p 5 -and C 2 -p 5 -C 70 Ph 6 are 0.49 and 1.41 eV, respectively, so once again the reported data are better explained by assuming that the isomer of C 70 Ph 6 that has been isolated and studied in the past [27,28,39] is in fact the C 2 -p 5 isomer. However, all possible C 1 -p 3 isomers have a CF 3 group attached to a triple-hexagon junction, and the DFT calculations predict that even the most stable of these is too high in energy to be a viable candidate for the structure of the isolated isomer.…”

Photophysical Properties of the Ground and Triplet State of Four Multiphenylated [70]Fullerene Compounds

“…We note that isomer 2 is the thermodynamically more stable compound but, from kinetic considerations, formation of isomer 1, characterised by successive 1,4 additions, may be favoured. [19] Both this study and that of Coheur et al [19] support regioisomer 2 rather than isomer 1, which was predicted from NMR data [17] as being the most probable structure of C 70 Ph 6 . Figure 3 g shows large phenyl contributions of about 30 % in the EDV spectrum at E 1.57 and 2.35 eV (790 and 528 nm).…”

“…[17] The predicted regioisomer of C 70 Ph 4 has a fullerene cage-centred chromophore consisting of 20 six-membered and 8 five-membered carbon rings. The C 70 molecule itself contains 25 hexagons and 12 pentagons.…”