Excellentπ-Bowl Semiconductors Based on C_(70)Subunit

As open substructures of fullerenes,aromaticπ-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)symmetricπ-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 threeπ-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 ofπ-bowls.1H NMR titration study indicated that the TES-ethynyl substituent enhanced the ability ofπ-bowl to bind C_(70)with an association constant of 2485 M−1.The C_(70)molecules withπ-bowls 3 and 6 formed 1:1 complexes,in which C_(70)molecules aggregated into zig-zag and 1D linear arrays,respectively.The hole mobility of 2.3 cm^(2)V^(−1)^s(−1)and electron mobility of 0.16 cm^(2)V^(−1)^s(−1)ofπ-bowl 3 and its complex with C_(70)were demonstrated,respectively,which proved a great value for the development of aromaticπ-bowl semiconductors with tunable properties for organic electronic devices.