Columnar assembled pyridyl bis-urea macrocycles 1 provide a strong 1D supramolecular synthon to construct hierarchical assemblies. These 1D pillars contain ditopic symmetrical acceptors in the form of basic oxygen lone pairs. Herein, we probe this synthon with a series of activated halogen bond donors, the regio-isomers of diiodotetrafluorobenzenes, which vary the relative orientation of the halogen bond formers. Irrespective of the initial stoichiometry, each donor only formed one type of co-crystal with 1. In each case, similar strong pillars of assembled 1 were observed that organize the donors through the CO⋯I interaction, which were significantly shorter than the sum of the van der Waals radii of the atoms involved and among the shortest reported for neutral organic molecules. X-ray photoelectron spectroscopy characteristic core level shifts strongly indicated the formation of halogen bonding interactions. These studies suggest that this synthon can utilize both hydrogen and halogen bonding orthogonally to build complex structures.

The reaction of cis-bis(2,2′-bipyridine)dichlororuthenium(II) hydrate with a conformationally mobile bipyridyl macrocycle afforded [(bpy)2Ru(μ-L)Ru(bpy)2]Cl4·6H2O, a bridged di-Ru complex. Single crystal X-ray diffraction showed the macrocyclic ligand adopting a bowl-like structure with the exo-coordinated Ru(II) centers separated by 7.29 Å. Photophysical characterization showed that the complex absorbs in the visible region (λmax = 451 nm) with an emission maximum at 610 nm (τ = 706 ns, ΦPL = 0.021). Electrochemical studies indicate the di-Ru complex undergoes three one-electron reversible reductions and a reversible one-electron oxidation process. This electrochemical reversibility is a key characteristic for its use as an electron transfer agents. The complex was evaluated as a photocatalyst for the electronically mismatched Diels–Alder reaction of isoprene and trans-anethole using visible light. It afforded the expected product in good conversion (69%) and selectivity (dr > 10:1) at low loadings (0.5–5.0 mol%) and the sensitizer/catalyst was readily recycled. These results suggest that the bipyridyl macrocycle could be widely applied as a bridging ligand for the generation of chromophore-catalyst assemblies.

Here, we compare structures determined by X-ray diffraction and subsequent Hirshfeld surface analysis to identify and understand the non-covalent interactions within the lattices of chromone, 6-methylchromone, 6-methoxychromone, 6-fluorochromone, and 6-chlorochromone with reported 6-bromochromone. In chromone, H-bonds and CH–л interactions predominate. H-bonds and aryl-stacking interactions are distinct in 6-methylchromone and 6-methoxychromone. The 6-fluorochromone, showed two types of H-bonds with O···H bonds having a greater contribution than F···H. In contrast, 6-chlorochromone and 6-bromochromone, the halogen contributes the larger percentage of stabilizing H-bonding with Cl···H and Br···H predominating over the O···H bonds. Compound 1 crystallizes in the monoclinic space group P21/n with a = 8.1546(8) Å, b = 7.8364(7) Å, c = 11.1424(11) Å, β = 108.506(2)° and Z = 4. Compound 2 crystallizes in the triclinic space group P-1 with a = 7.0461(3) Å, b = 10.2108(5) Å, c = 10.7083(5) Å, α = 89.884(2)°, β = 77.679(2)°, γ = 87.367(2)° and Z = 4. Compound 3 crystallizes in the monoclinic space group P21/n with a = 8.1923(4) Å, b = 7.0431(3) Å, c = 15.3943(8) Å, β = 92.819(2)° and Z = 4. Compound 4 crystallizes in the triclinic space group P1 with a = 3.7059(2) Å, b = 6.1265(4) Å, c = 7.6161(5) Å, α = 84.085(3)°, β = 87.070(3)°, γ = 83.390(3)° and Z = 1. Compound 5 crystallizes in the monoclinic space group P21 with a = 3.8220(2) Å, b = 5.6985(2) Å, c = 16.9107(7) Å, β = 95.8256(18)° and Z = 2.

•Chromone and four derivatives were absorbed in a self-assembled bis-urea host.•Loading of guests and the binding ratios were analyzed by UV-Vis spectroscopy.•Photolysis of host·chromone, host·6-fluorochromone afforded anti-HT photodimers.•Photolysis of host·6-bromochromone afforded an unusual aryl coupling product.•Structures of the host·guest complexes were investigated by GCMC simulations.This manuscript reports on the modulation of the photoreactivity of a series of chromones, also known as benzo-γ-pyrones, by absorption into a porous self-assembled host formed from phenylethynylene bis-urea macrocycles. Chromone and four derivatives namely 6-fluorochromone, 6-bromochromone, 7-hydroxy-4-chromone, and 3-cyanochromone are unreactive in the solid-state. Each of these derivatives was loaded into the nanochannels of self-assembled phenylethynylene bis-urea macrocycles to form solid host·guest complexes, which were subsequently UV-irradiated at room temperature under argon atmosphere. We observed that chromone and 6-fluorochromone underwent selective [2 + 2] photodimerization reactions to produce anti-HT dimers in high selectivity and conversion. The 6-bromochromone also reacted in high selectivity and conversion to afford an aryl coupling adduct. In each case, the products were extracted, and the crystalline host recovered. In comparison, 7-hydroxy-4-chromone, and 3-cyanochromone were unreactive within the complex. Simple GCMC simulation studies suggest that chromone, 6-fluorochromone, and 6-bromochromone were loaded in orientations that facilitate photoreaction, and correctly predicted that the anti-HT dimer would be favored in the chromone case. In contrast, syn-HH dimers were predicted by GCMC simulations for the halogen containing derivatives but were not observed. The simulations with 7-hydroxy-4-chromone were in agreement with the observed reactivity. We compare these computational and experimental findings and suggest future methods for optimizing simulation parameters. Our goal is to expand the scope and accuracy of the simulations to be able to predict the reactivity of guests encapsulated within columnar nanotubes.

Urea is a versatile building block that can be modified to self-assemble into a multitude of structures. One-dimensional nanochannels with zigzag architecture and cross-sectional dimensions of only ∼3.7 Å × 4.8 Å are formed by the columnar assembly of phenyl ether bis-urea macrocycles. Nanochannels formed by phenylethynylene bis-urea macrocycles have a round cross-section with a diameter of ∼9.0 Å. This work compares the Xe atom packing and diffusion inside the crystalline channels of these two bis-ureas using hyperpolarized Xe-129 NMR. The elliptical channel structure of the phenyl ether bis-urea macrocycle produces a Xe-129 powder pattern line shape characteristic of an asymmetric chemical shift tensor with shifts extending to well over 300 ppm with respect to the bulk gas, reflecting extreme confinement of the Xe atom. The wider channels formed by phenylethynylene bis-urea, in contrast, present an isotropic dynamically average electronic environment. Completely different diffusion dynamics are revealed in the two bis-ureas using hyperpolarized spin-tracer exchange NMR. Thus, a simple replacement of phenyl ether with phenylethynylene as the rigid linker unit results in a transition from single-file to Fickian diffusion dynamics. Self-assembled bis-urea macrocycles are found to be highly suitable materials for fundamental molecular transport studies on micrometer length scales.Keywords: bis-urea; hyperpolarization; nanotubes; SEOP; single-file diffusion; spin-exchange optical pumping; xenon-129;

The porous molecular crystals prepared through the self-assembly of bis-urea macrocycles display surface areas similar to zeolites but lower than MOFs. Their simple one-dimensional channels are well-suited for studying binding, investigating transport, diffusion and exchange, and monitoring the effects of encapsulation on reaction mechanism and product distribution. Guests that complement the size, shape, and polarity of the channels can be absorbed into these porous crystals with repeatable stoichiometry to form solid host–guest complexes. Heating or extraction with an organic solvent enables desorption or removal of the guest and subsequent recovery of the solid host. Further, these porous crystals can be used as containers for the selective [2 + 2] cycloadditions of small enones such as 2-cyclohexenone or 3-methyl-cyclopentenone, while larger hosts bind and facilitate the photodimerization of coumarin. When the host framework incorporates benzophenone, a triplet sensitizer, UV-irradiation in the presence of oxygen efficiently generates singlet oxygen. Complexes of this host were employed to influence the selectivity of photooxidations of 2-methyl-2-butene and cumene with singlet oxygen. Small systematic changes in the channel and bound reactants should enable systematic evaluation of the effects of channel dimensions, guest dimensions, and channel–guest interactions on the processes of absorption, diffusion, and reaction of guests within these nanochannels. Such studies could help in the development of new materials for separations, gas storage, and catalysis.

This manuscript describes a single-crystal-to-single-crystal polymerization of the dihydrate of diacetylene 1 (1·2H2O) to give an unusual polydiacetylene (PDA) structure that consists of aligned nanotubes, with each covalently bonded nanotube having two parallel PDA chains that run parallel down opposite sides of a channel defined by the macrocycle. Each PDA nanotube is connected with four other columns via amide hydrogen bonds with an N-(H)···O distance of 2.888(4) Å. Such well-ordered polymers should display quasi-one-dimensional electronic structures and may be of interest for the formation of highly conductive organic materials. We obtained the 1·2H2O form in bulk, which was polymerized by heating. Powder X-ray diffraction suggests that bulk PDA powder is single phase and displays a similar structure as the PDA single crystals. Furthermore, we showed that PDA crystals absorbed I2 vapor. We believe that this unique PDA structure, which is amenable to property control via adsorbed guests, will be an attractive one for investigating charge-transfer doping in PDA-based organic electronic materials. We also observed two additional crystal forms, including 1·MeOH, which also shows a columnar assembly, and a tetrahydrate 1·4H2O that shows water tetramers that link four cycles into a 2D sheet structure.

A carbonate–stilbene bifunctional macrocycle was readily synthesized, and its assembly was studied by crystallization from several solvents. The macrocycle displayed columnar assembly from less polar solvents (THF and CH2Cl2), while a more compact structure was observed from 9:1 CH2Cl2–acetone. All structures displayed organization through the C–H⋯O hydrogen bonding motif as well as through aryl stacking interactions. Upon dissolution and treatment with Grubbs’ II catalyst, this 30-membered ring underwent entropy-driven ring-opening metathesis polymerization (ED-ROMP) to give a precisely linear alternating A–B–A–B copolymer. This design of a single macrocyclic building block allows the formation of supramolecular self-assembly in the solid-state while affording a linear alternating polymer from solution.

Confined environments can be used to alter the selectivity of a reaction by influencing the organization of the reactants, altering the mobility of trapped molecules, facilitating one reaction pathway or selectively stabilizing the products. This manuscript utilizes a series of potentially photoreactive guests to interrogate the utility of the one-dimensional nanochannels of a porous host to absorb and facilitate the reaction of encapsulated guests. The host is a columnar self-assembled phenylethynylene bis-urea macrocycle, which absorbs guests, including coumarin, 6-methyl coumarin, 7-methyl coumarin, 7-methoxy coumarin, acenaphthylene, cis-stilbene, trans-stilbene, and trans-β-methylstyrene to afford crystalline inclusion complexes. We examine the structure of the host:guest complexes using powder X-ray diffraction, which suggests that they are well-ordered highly crystalline materials. Investigations using solid-state cross-polarized magic angle spinning 13C{1H}CP-MAS NMR spectroscopy indicate that the guests are mobile relative to the host. Upon UV-irradiation, we observed selective photodimerization reactions for coumarin, 6-methyl coumarin, 7-methyl coumarin, and acenaphthylene, while the other substrates were unreactive even under prolonged UV-irradiation. Grand Canonical Monte Carlo simulations suggest that the reactive guests were close paired and preorganized in configurations that facilitate the photodimerization with high selectivity while the unreactive guests did not exhibit similar close pairing. A greater understanding of the factors that control diffusion and reaction in confinement could lead to the development of better catalysts.

Co-crystals formed from pyridyl bis-urea macrocycles and iodopentafluorobenzene or diiodotetrafluoroethane show surprisingly short, strong halogen bonds. The shortest interactions were observed between the carbonyl oxygen and the iodide and were 78% of the sum of the van der Waals radii for O⋯I, with distances ranging from 2.719(2) to 2.745(2) Å.

This manuscript investigates how incorporation of benzophenone, a well-known triplet sensitizer, within a bis-urea macrocycle, which self-assembles into a columnar host, influences its photophysical properties and affects the reactivity of bound guest molecules. We further report the generation of a remarkably stable organic radical. As expected, UV irradiation of the host suspended in oxygenated solvents efficiently generates singlet oxygen similar to the parent benzophenone. In addition, this host can bind guests such as 2-methyl-2-butene and cumene to form stable solid host–guest complexes. Subsequent UV irradiation of these complexes facilitated the selective oxidation of 2-methyl-2-butene into the allylic alcohol, 3-methyl-2-buten-1-ol, at 90% selectivity as well as the selective reaction of cumene to the tertiary alcohol, α,α′-dimethyl benzyl alcohol, at 63% selectivity. However, these products usually arise through radical pathways and are not observed in the presence of benzophenone in solution. In contrast, typical reactions with benzophenone result in the formation of the reactive singlet oxygen that reacts with alkenes to form endoperoxides, diooxetanes, or hydroperoxides, which are not observed in our system. Our results suggest that the confinement, the formation of a stable radical species, and the singlet oxygen photoproduction are responsible for the selective oxidation processes. A greater understanding of the mechanism of this selective oxidation could lead to development of greener oxidants.

A one-dimensional crystalline solid built from pillars of self-assembled bis-urea pyridyl macrocycles affords a close packed structure with no pores. These organic pillars contain unsatisfied urea oxygen lone pairs that can be used to drive the absorption of alcohols including trifluoroethanol, phenol, pentafluorophenol, and ethylene glycol to give well-ordered host:guest complexes with repeatable stoichiometry. The driving force for reversible solid transitions appears to be the formation of hydrogen bonds between the guest and an unsatisfied hydrogen bond acceptor, which is a lone pair of the urea oxygen. Halogen bonding with the electrophilic iodide in pentafluoroiodobenzene can also drive absorption by the host to give a well-ordered host:guest complex. These results suggest that the organic solid-state is surprisingly dynamic and may have potential applications for sorbents.Keywords: guest absorption; porous crystals; solid-to-solid transformation; ureas;

The reaction of cis-bis(2,2′-bipyridine)dichlororuthenium(II) hydrate with a conformationally mobile bipyridyl macrocycle afforded [(bpy)2Ru(μ-L)Ru(bpy)2]Cl4·6H2O, a bridged di-Ru complex. Single crystal X-ray diffraction showed the macrocyclic ligand adopting a bowl-like structure with the exo-coordinated Ru(II) centers separated by 7.29 Å. Photophysical characterization showed that the complex absorbs in the visible region (λmax = 451 nm) with an emission maximum at 610 nm (τ = 706 ns, ΦPL = 0.021). Electrochemical studies indicate the di-Ru complex undergoes three one-electron reversible reductions and a reversible one-electron oxidation process. This electrochemical reversibility is a key characteristic for its use as an electron transfer agents. The complex was evaluated as a photocatalyst for the electronically mismatched Diels–Alder reaction of isoprene and trans-anethole using visible light. It afforded the expected product in good conversion (69%) and selectivity (dr > 10:1) at low loadings (0.5–5.0 mol%) and the sensitizer/catalyst was readily recycled. These results suggest that the bipyridyl macrocycle could be widely applied as a bridging ligand for the generation of chromophore-catalyst assemblies.