Polycyclic aromatic hydrocarbons (PAHs) represent a large family of molecular building blocks based on multiple fused aromatic rings. The fact that the concave and convex surfaces of buckybowls, on one hand, and their edges, on the other hand, are readily available for reactions offers intriguing possibilities in chemistry. Buckybowls have been targeted as molecular building blocks toward more complex carbon nanoforms such as carbon nanotubes.¹ Finally, and most importantly, buckybowls show unique electronic properties, often in between those of flat PAHs and fullerenes, which can be skillfully exploited for organic electronics applications.

With regard to supramolecular chemistry, buckybowls have been studied thoroughly as hosts for fullerenes owing to their shape complementarity. However, the association of buckybowls by other organic hosts has hardly been investigated. Recently, we described the association of a fullerene fragment, hemifullerene C₃₀H₁₂, by an electron-donating, bowl-shaped tetrathiafulvalene derivative (truxTTF), in which three 1,3-dithiole rings are attached to a truxene core.² The stability of the associate was remarkable, with an association constant of log Ka = 3.6±0.3 in CHCl₃ at room temperature. Moreover, we demonstrated photoinduced electron transfer from truxTTF to C₃₀H₁₂ to form the fully charge-separated species, which constituted the first example in which a buckybowl mimicked the electron-accepting properties of fullerenes within supramolecular complexes.²

In contrast to hemifullerene C₃₀H₁₂, the recently reported larger C₃₂H₁₂ and C₃₈H₁₄ buckybowls are corannulene-based fragments of [60] and [70]fullerene, respectively. Such a difference in core aromatic structure is likely to be accompanied by fundamental differences in electronic properties. Here, we demonstrate that truxTTF forms heteromolecular associates with C₃₂H₁₂ and C₃₈H₁₄ in a variety of organic solvents.³ Density functional theory (DFT) calculations showed several different approximations of the heteromolecular complexes, all with favorable interaction energies, but only one, that is, the staggered arrangement, with a significant negative free energy of complexation. NMR experiments confirmed the formation of staggered structures for both heterodimers in solution. Spectroelectrochemical and transient absorption studies revealed that photoinduced electron transfer (PET) occurs in truxTTF·C₃₈H₁₄, thus showing that corannulene p-extended derivatives resemble the electronic behavior of [60]fullerene.

References

1. a) U. H. F. Bunz, S. Menning, N. Martín, "para-Connected Cyclophenylenes and Hemispherical Polyarenes: Building Blocks for Single Walled Carbon Nanotubes?" Angew. Chem. Int. Ed., 2012, 51, 7094-7101; b) E. M. Pérez, N. Martín, " π–π interactions in carbon nanostructures" Chem. Soc. Rev., 2015, 44, 6425-6433.
2. M. Gallego, J. Calbo, J. Aragó, R. M. Krick Calderon, F. H. Liquido, T. Iwamoto, A. K. Greene, E. A. Jackson, E. M. Pérez, E. Ortí, D. M. Guldi, L. T. Scott, N. Martín, Angew. Chem. Int. Ed., 2014, 53, 2170-2175.
3. M. Gallego, J. Calbo, R. M. Krick Calderon, P. Pla, Y. Hsieh, E. M. Pérez, Y. Wu, E. Ortí, D. M. Guldi, N. Martín, Chem. Eur. J. 2017, 23, 3666-3673.