Excellent π-Bowl Semiconductors Based on C₇₀ Subunit

As open substructures of fullerenes, aromatic π-bowls are promising candidates as new organic semiconductors, as well as attractive hosts for fullerenes. We demonstrate herein the synthesis and characterization of a novel C_2v symmetric π-bowl, pyracyleno [6, 5, 4, 3, 2, 1-pqrstuv]pentaphene (3). Bowl 3 was equipped with two distinctive reactive sites, allowing for bromination and cross-coupling reactions to readily yield functionalized bowls with two 2, 4, 6-trimethylphenyl (5) and triethylsilyl (TES)-ethynyl (6) substituents, respectively. Variable-temperature ¹H NMR analysis and density functional theory (DFT) calculations indicated bowl-to-bowl inversions of 3, 5, and 6 at room temperature. By alternating the substituents, the crystal structures of the three π-bowls 3, 5, and 6 could be controlled from 1D linear to 1D slipped to 2D herringbone packing motifs, providing insight into the packing behavior of π-bowls. ¹H NMR titration study indicated that the TES-ethynyl substituent enhanced the ability of π-bowl to bind C₇₀ with an association constant of 2485 M⁻¹. The C₇₀ molecules with π-bowls 3 and 6 formed 1:1 complexes, in which C₇₀ molecules aggregated into zig-zag and 1D linear arrays, respectively. The hole mobility of 2.3 cm² V⁻¹ s⁻¹ and electron mobility of 0.16 cm² V⁻¹ s⁻¹ of π-bowl 3 and its complex with C₇₀ were demonstrated, respectively, which proved a great value for the development of aromatic π-bowl semiconductors with tunable properties for organic electronic devices.