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We report the design, synthesis, and crystal structure of a conjugated aryleneethynyl molecule, 2-(2-{4,5-dimethoxy-2-[2-(2,3,4-trifluorophenyl)ethynyl]phenyl}ethynyl)-6-[2-(pyridin-2-yl)ethynyl]pyridine, C 30 H 17 F 3 N 2 O 2 , that adopts a planar rhombus conformation in the solid state. The molecule crystallizes in the space group P -1, with Z = 2, and features two intramolecular sp 2 -C—H...N hydrogen bonds that co-operatively hold the arylethynyl molecule in a rhombus conformation. The H atoms are activated towards hydrogen bonding since they are situated on a trifluorophenyl ring and the H...N distances are 2.470 (16) and 2.646 (16) Å, with C—H...N angles of 161.7 (2) and 164.7 (2)°, respectively. Molecular electrostatic potential calculations support the formation of C—H...N hydrogen bonds to the trifluorophenyl moiety. Hirshfeld surface analysis identifies a self-complementary C—H...O dimeric interaction between adjacent 1,2-dimethoxybenzene segments that is shown to be common in structures containing that moiety. 

Recently discovered diamond nanothreads offer a stiff, sp 3 -hybridized backbone unachievable in conventional polymer synthesis that is formed through the solid-state pressure-induced polymerization of simple aromatics. This method enables monomeric A-B alternation to fully translate from co-crystal design to polymer backbone in a sequence-defined manner. Here, we report the compression of aryl:perfluoroaryl (Ar/ArF) co-crystals containing –OH and –CHO functional groups. We analyze the tolerance of these functional groups to polymerization, explore the possibility of keto–enol tautomerization, and compare the reaction outcomes of targeted solid-state Ar/ArF design on nanothread formation. Two new co-crystals comprising phenol:pentafluorobenzaldehyde (ArOH:ArFCHO) and benzaldehdye:pentafluorophenol (ArCHO:ArFOH) were synthesized through slow solvent evaporation. Analysis of the single-crystal structures revealed different hydrogen bonding patterns between the –OH and –CHO in each solid (tape and orthogonal dimers, respectively), in addition to markedly different π–π stacking distances within the Ar/ArF synthons. In situ Raman spectroscopy was used to monitor the compression of each co-crystal to 21 GPa and illustrated peak shifts for the –OH and –CHO stretching regions during compression. Photoluminescence corresponding to polymerization appeared at a lower pressure for the co-crystal with the smallest π–π stacking distance. Nevertheless, the recovered solid with the larger centroid : centroid and centroid : plane π–π stacking distances featured a diffraction ring consistent with the anticipated dimensions of a co-crystal-derived nanothread packing, indicating that both functional group interactions and parallel stacking affect the pressure-induced polymerization to form nanothreads. IR spectroscopy of the recovered samples revealed large shifts in the –OH & –CHO stretching regions, particularly noticable for ArCHO:ArFOH, which may reflect geometrical constraints associated with forming a rigid thread backbone under pressure. Simulation suggests that hydrogen bonding networks may affect the relative compressibility of the co-crystal along a thread-forming axis to modulate the propensity for nanothread formation. 

A halogen-bonded eight-fold interpenetrated diamondoid net was constructed employing a node generated in the solid state. Specifically, co-crystallization of a tetrahedral-like tecton, rctt -tetrakis(4-pyridyl)cyclobutane (4,4′-TPCB), combined with a rigid halogen-bond donor, 1,4-diiodoperchlorobenzene, achieved a diamondoid architecture. In the co-crystal, 4,4′-TPCB is found to form three types of linkages based on one cis - and two trans -orientations enabled by the intrinsic rctt -stereochemisty of the central cyclobutane ring. Thus, 4,4′-TPCB is able to adapt to the constraints of the diamondoid net owing to the flexibility of the pendant 4-pyridyl groups. 

Limited supramolecular strategies have been utilized to synthesize sequence-defined polymers, despite the prominence of noncovalent interactions in materials design. Herein, we illustrate the utility of ‘sacrificial’ aryl-perfluoroaryl supramolecular synthons to synthesize sp 3 -hybridized nanothreads from sp 2 -enriched reactants. Our strategy features A–B reactant pairs in the form of a phenol:pentafluorophenol co-crystal that is preorganized for an electronically-biased and sequence-defined polymerization. The polymerization, initiated at 12 GPa, affords an alternating copolymer featuring exogenous –OH functionalities. The external substitution is confirmed through IR spectroscopy. Importantly, the inclusion of the functional unit provides the first experimental glimpse at reaction mechanism: keto–enol tautomerization that can only occur during cycloaddition is observed through IR spectroscopy. Our approach realizes the first example of a functionalized nanothread and attains sequence definition through sacrificial supramolecular preorganization and presents a further approach for de novo design of complex nanothreads. 

Terahertz (THz) spectroscopy has been put forth as a non-contact, analytical probe to characterize the intermolecular interactions of biologically active molecules, specifically as a way to understand, better develop, and use active pharmaceutical ingredients. An obstacle towards fully utilizing this technique as a probe is the need to couple features in the THz regions to specific vibrational modes and interactions. One solution is to use density functional theory (DFT) methods to assign specific vibrational modes to signals in the THz region, coupling atomistic insights to spectral features. Here, we use open source planewave DFT packages that employ ultrasoft pseudopotentials to assess the infrared (IR) response of organic compounds and complex co-crystal formulations in the solid state, with and without dispersion corrections. We compare our DFT computed lattice parameters and vibrational modes to experiment and comment on how to improve the agreement between theory and modeling to allow for THz spectroscopy to be used as an analytical probe in complex biologically relevant systems. 

A three-dimensional hydrogen-bonded network based on a rare mok topology has been constructed using an organic molecule synthesized in the solid state. The molecule is obtained using a supramolecular protecting-group strategy that is applied to a solid-state [2+2] photodimerization. The photodimerization affords a novel head-to-head cyclobutane product. The cyclobutane possesses tetrahedrally disposed cis -hydrogen-bond donor (phenolic) and cis -hydrogen-bond acceptor (pyridyl) groups. The product self-assembles in the solid state to form a mok network that exhibits twofold interpenetration. The cyclobutane adopts different conformations to provide combinations of hydrogen-bond donor and acceptor sites to conform to the structural requirements of the mok net. 

Nano-dimensional single crystals of acetylsalicylic acid (aspirin) Form I are generated through sonocrystallization and are shown to exhibit Young's modulus values in the MPa range, which is significantly softer (5-fold reduction) than macro-dimensional single crystals. The change is attributed to structural consequences of the size-dependent surface-to-volume ratio effect, particularly as related to intermolecular forces.