Buckybowl is first of its kind

If you could smash a buckyball with a hammer, you might be left with a lot of little pieces. These buckyball fragments are called buckybowls, and their strained structures—and the laws of physics—mean making them is a lot harder than swinging a hammer. Now Jishan Wu and colleagues at the National University of Singapore have synthesized a seven-ringed fragment of a 70-carbon buckyball for the first time (J. Am. Chem. Soc. 2019, DOI: 10.1021/jacs.9b03169). They started with a five-ringed rylene molecule, then performed alkylation steps to add two five-membered rings and complete the buckybowl. The resulting molecule is slightly concave and dish-like. It’s antiaromatic, which the researchers confirmed using nuclear magnetic resonance and with computer modeling. Aryl substituents maintain this electronic structure by preventing radical formation, and the bulk allowed the researchers to obtain a crystal structure. NMR revealed that the bowl, which is about 0.9 Å deep, oscillates at room temperature, flipping inside out and back again. Computer models showed that the dication form of the C₇₀ buckybowl has an electronic structure with concentric rings of conjugated π orbitals. Wu says the molecule’s small band gap and ability to act as both an acid and a base could make it useful as an ambipolar semiconductor. He says the group is now working to synthesize larger and deeper buckybowls.