Evidence for Functionalized Carbon Nanothreads from π-Stacked, para-Disubstituted Benzenes

Abstract

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 π-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 π-stacking, wherein the stacking distance between parallel planes of monomers and the slippage angle between π-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 π-stacking polymerization may lead to the realization of well-defined organic nanostructures with designed functionality.

Perfect and Defective 13C-Furan-Derived Nanothreads from Modest-Pressure Synthesis Analyzed by 13C NMR

“…Saturated carbon nanothreads, which fill the one-dimension/sp 3 entry in this matrix of dimensionality and hybridization, were first synthesized by high-pressure solid-state polymerization of benzene. 16,17 Since then, a wide variety of nanothreads consisting primarily of sp 3 -hybridized carbon have been synthesized by pressure-induced polymerization of aromatic molecules (e.g., pyridine, thiophene and aniline), [18][19][20][21][22] co-crystals (e.g., naphthalene-octafluoronaphthalene, phenol-pentafluorophenol), [23][24][25][26][27] and a strained saturated hydrocarbon, cubane. 28 Pressure-induced solid-state reaction thus appears to be a general means of obtaining ordered packings of one-dimensional, high-aspect ratio diamond-like backbones decorated with diverse heteroatoms and functional groups, living at the threshold of thickness where framework rigidity first emerges in solids, a regime rife with promise for novel chemical and physical properties.…”

Perfect and Defective 13C-Furan-Derived Nanothreads from Modest-Pressure Synthesis Analyzed by 13C NMR

“…pyridine, thiophene and aniline), [18][19][20][21][22] co-crystals (e.g. naphthalene-octafluoronaphthalene, phenol-pentafluorophenol), [23][24][25][26] and a strained saturated hydrocarbon, cubane. 27 Pressure-induced solid-state reaction thus appears to be a general means of obtaining ordered packings of one-dimensional, high-aspect ratio diamond-like backbones decorated with diverse heteroatoms and functional groups, living at the threshold of thickness where framework rigidity first emerges in solids, a regime rife with promise for novel chemical and physical properties.…”

“…27 Pressure-induced solid-state reaction thus appears to be a general means of obtaining ordered packings of one-dimensional, high-aspect ratio diamond-like backbones decorated with diverse heteroatoms and functional groups, living at the threshold of thickness where framework rigidity first emerges in solids, a regime rife with promise for novel chemical and physical properties. [28][29][30][31] Advances in our understanding of nanothread synthesisincluding the roles of temperature, 19,21 aromaticity, 22 molecular stacking geometry, [23][24][25][26] compression rate, 16,17,22,24 and uniaxiality of stress 16,17,20,22 have been accompanied by substantial reductions in synthesis pressure, convincing demonstrations of sp 3 character, and initial ascertainments of axial periodicity, 32 but not yet by a clear determination of the precise atomic structure of regular, periodic regions of saturated thread backbone.…”

Perfect and Defective 13C-Furan-Derived Nanothreads from Modest-Pressure Synthesis Analyzed by 13C NMR

“…Saturated carbon nanothreads, which fill the one-dimension/sp 3 entry in this matrix of dimensionality and hybridization, were first synthesized by high-pressure solid-state polymerization of benzene. 16,17 Since then, a wide variety of nanothreads consisting primarily of sp 3 -hybridized carbon have been synthesized by pressure-induced polymerization of aromatic molecules (e.g., pyridine, thiophene and aniline), [18][19][20][21][22] co-crystals (e.g., naphthalene-octafluoronaphthalene, phenol-pentafluorophenol), [23][24][25][26][27] and a strained saturated hydrocarbon, cubane. 28 Pressure-induced solid-state reaction thus appears to be a general means of obtaining ordered packings of one-dimensional, high-aspect ratio diamond-like backbones decorated with diverse heteroatoms and functional groups, living at the threshold of thickness where framework rigidity first emerges in solids, a regime rife with promise for novel chemical and physical properties.…”

“…28 Pressure-induced solid-state reaction thus appears to be a general means of obtaining ordered packings of one-dimensional, high-aspect ratio diamond-like backbones decorated with diverse heteroatoms and functional groups, living at the threshold of thickness where framework rigidity first emerges in solids, a regime rife with promise for novel chemical and physical properties. [29][30][31][32] Advances in our understanding of nanothread synthesisincluding the roles of temperature, 19,21 aromaticity, 22 molecular stacking geometry, [23][24][25][26] compression rate, 16,17,22,24 and uniaxiality of stress 16,17,20,22 have been accompanied by substantial reductions in synthesis pressure, convincing demonstrations of sp 3 character, 33,[18][19][20][21][22] and initial ascertainments of axial periodicity, 27 but not yet by a clear determination of the precise atomic structure of regular, periodic regions of saturated thread backbone.…”