Evidence for Functionalized Carbon Nanothreads from π-Stacked, <i>para</i>-Disubstituted Benzenes

Recent studies of highly compressed organic molecules reveal the synthesis of one-dimensional (1D) nanothread structures, typically formed through addition reactions of unsaturated bonds. Although these nanostructures have been demonstrated from molecules such as benzene, pyridine, and thiophene, it remains unclear whether functionalized nanothreads can be produced from precursors with different substituent groups under high-pressure conditions. Here, we examine the controlled pressure-induced polymerization of several para-disubstituted benzene molecular crystals and cocrystals with different functional groups including dinitrobenzene, diethynylbenzene, and dicyanobenzene. X-ray diffraction and infrared spectroscopy provide evidence for the formation of ordered nanostructures that maintain their topological relationship with the starting molecular phase and preserve initial functionality. Although no clear correlation between specific functional groups and polymerization pressure was observed, the proximity toward sandwich-type pi-stacking within the starting molecular crystals influences reaction pathway selectivity and the formation of new saturated bonds under normal compression conditions. We propose a simple correlation related to pi-stacking, wherein the stacking distance between parallel planes of monomers and the slippage angle between pi-stacks are important aspects that influence polymerization pathway selectivity and the formation of ordered products under normal compression at room temperature. Functionalized nanothread structures are possible through careful precursor selection, and an improved understanding of pi-stacking polymerization may lead to the realization of well-defined organic nanostructures with designed functionality.