A Shape‐Persistent Quadruply Interlocked Giant Cage Catenane with Two Distinct Pores in the Solid State

An S10-Symmetric 5-Fold Interlocked [2]Catenane

The reaction of sym-pentakis(4-aminothiophenyl)corannulene with 2-formyl-6-methylpyridine and Cu^I or 2-formyl-1,10-phenanthroline and M^II (M = Co, Zn) yields an S₁₀-symmetric 5-fold interlocked [2]catenane of two interpenetrating [Cu^I₅L₂]⁵⁺ cages or D₅-symmetric [M^II₅L₂]¹⁰⁺ cages, respectively. The new structures were characterized by X-ray crystallography, NMR spectroscopy, and mass spectrometry. Density functional theory computations point to dispersive energies on par with traditional covalent bond energies. Subcomponent exchange reactions favored formation of the [Co^II₅L₂]¹⁰⁺ cage over the [Cu^I₁₀L₄]¹⁰⁺ catenane. The single cage and catenane each cocrystallized with a corannulene guest to form a bowl-in-bowl substructure.

Organic Cage Dumbbells

Molecular dumbbells with organic cage capping units were synthesised via a multi-component imine condensation between a tri-topic amine and di- and tetra-topic aldehydes. This is an example of self-sorting, which can be rationalised by computational modelling.

Host-Guest Recognition and Fluorescence of a Tetraphenylethene-Based Octacationic Cage

We report the synthesis and characterization of a three-dimensional tetraphenylethene-based octacationic cage that shows host-guest recognition of polycyclic aromatic hydrocarbons (e.g. coronene) in organic media and water-soluble dyes (e.g. sulforhodamine 101) in aqueous media through CH⋅⋅⋅π, π-π, and/or electrostatic interactions. The cage⊃coronene exhibits a cuboid internal cavity with a size of approximately 17.2×11.0×6.96 ų and a "hamburger"-type host-guest complex, which is hierarchically stacked into 1D nanotubes and a 3D supramolecular framework. The free cage possesses a similar cavity in the crystalline state. Furthermore, a host-guest complex formed between the octacationic cage and sulforhodamine 101 had a higher absolute quantum yield (Φ_F =28.5 %), larger excitation-emission gap (Δλ_ex-em =211 nm), and longer emission lifetime (τ=7.0 ns) as compared to the guest (Φ_F =10.5 %; Δλ_ex-em =11 nm; τ=4.9 ns), and purer emission (Δλ_FWHM =38 nm) as compared to the host (Δλ_FWHM =111 nm).

Rational design of crystalline two-dimensional frameworks with highly complicated topological structures

Constructing two-dimensional (2D) polymers with complex tessellation patterns via synthetic chemistry makes a significant contribution not only to the understanding of the emergence of complex hierarchical systems in living organisms, but also to the fabrication of advanced hierarchical materials. However, to achieve such tasks is a great challenge. In this communication we report a facile and general approach to tessellate 2D covalent organic frameworks (COFs) by three or four geometric shapes/sizes, which affords 2D COFs bearing three or four different kinds of pores and increases structural complexity in tessellations of 2D polymers to a much higher level. The complex tessellation patterns of the COFs are elucidated by powder X-ray diffraction studies, theoretical simulations and high-resolution TEM.

Constructing two-dimensional (2D) polymers with complex tessellation patterns is important for the fabrication of advanced materials but achieving such complexity is a great challenge. Here the authors report a tessellated 2D covalent organic framework with increased structural complexity as well as different pore structures.

A tetrahedral molecular cage with a responsive vertex

Dynamic covalent chemistry (DCC) is a widely used method for the self-assembly of three-dimensional molecular architectures. The orthogonality of dynamic reactions is emerging as a versatile strategy for controlling product distributions in DCC, yet the application of this approach to the synthesis of 3D organic molecular cages is limited. We report the first system which employs the orthogonality of alkyne metathesis and dynamic imine exchange to prepare a molecular cage with a reversibly removable vertex. This study demonstrates the rational and controlled application of chemical orthogonality in DCC to prepare organic cages of expanded functionality which respond to chemical stimuli.

The chemistry of multi-component and hierarchical framework compounds

This review is expected to provide a library of multi-component hierarchically porous compounds, which shall guide the state-of-the-art design of future porous materials with unprecedented tunability, synergism and precision.

Controllable Self-Assembly of Pills and Cages via Imine Condensation for Silver Cation Detection

By condensing a trisamino linker with one of the two analogous bisaldehyde ligands, pills and tetrahedrons could be self-assembled. The self-assembled preference could be controlled by tuning the reaction conditions, including the size of side chain, concentration, and temperature. Coordination of silver cation quenches the fluorescence of the fluorene moieties on the pill, opening up opportunities for Ag⁺ cation detection.

Porous Shape-Persistent Organic Cage Compounds of Different Size, Geometry, and Function

The interest in shape-persistent organic cages is nearly as old as the interest in supramolecular chemistry. In the beginning, organic cages have often been synthesized in a stepwise manner, which is not only laborious but very often also accompanied by low overall yields. In 1988, MacDowell published the one pot high-yielding synthesis of [2 + 3] imine cages based on TREN and aromatic dialdehydes, exploiting the reversible condensation of amines and aldehydes to  imines, which was later used by others to make even larger cages on the basis of resorcinarenes. In 2008, the synthesis and characterization of an adamantoid [4 + 6] imine cage by condensation of a C_{3 v}-symmetric triaminotriptycene and commercially available 4- tert-butyl salicyldialdehyde was introduced by the author, which was the ignition of our group activities in this research area. In 2011, we published the first gas-sorption data for this [4 + 6] imine cage: with a measured specific surface area of SA_BET = 1377 m²/g according to the model of Brunauer-Emmett-Teller (BET) this was twice as high as for the reported smaller cages of Cooper. For a second desolvated polymorph of the same cage, an even higher SA_BET = 2071 m²/g was determined; still one of the highest surface areas until date for porous organic molecular materials. Subsequently, the influence of the substituent in 4-position of the salicyldialdehyde for the reaction to [4 + 6] imine cages was investigated as well as the role of the phenolic hydroxyl group. It turned out that the phenolic hydroxyl group is crucial as directing group to increase the formation of the cage as well as stabilize the structure by cyclic six-membered intramolecular hydrogen bonds. The concept was extended to other imine-based cages of different geometry and size. For instance, a [4 + 4] cubic structure from triptycene trissalicylaldehyde and triptycene triamine was accessible as an amorphous insoluble solid, able to adsorb 18.2 wt % CO₂ at ambient conditions. To gain further insight into the structural needs of the molecular precursors, rigidity and preorientation of reacting sites were investigated on prismatic [2 + 3] and truncated tetrahedral [4 + 4] imine cages, showing that rigidity and preorientation is beneficial or even crucial for cage formation. Furthermore, chiral self-sorting was studied on the basic of racemic triamines. Besides imine condensation, we explored the reversible formation of boronic esters from boronic acids and diols. Triptycene tetraol with its 120° angle between the aromatic units has been used in the condensation with benzene triboronic acid to achieve a large cuboctahedral [12 + 8] cage with pore dimensions of 2 nm, which are by IUPAC definition mesoporous. After activation the measured specific surface area was SA_BET = 3758 m²/g, a number rarely achieved even for other porous compounds such as threedimensional framework materials. Smaller tetrahedral [4 + 6] boronic ester cages were synthesized too. These cages show a selective gas sorption with preference of saturated hydrocarbon ethane over ethylene and acetylene. What distinguishes porous materials derived from molecular cages from three-dimensional frameworks or networks the most is their solubility; thus, the cages are soluble porous units (SPUs) in a broader sense. Taking advantage of this, [4 + 6] imine cages were postfunctionalized in solution to change the gas sorption properties in the crystalline state. Furthermore, cage solutions were spray-coated onto quartz crystal microbalances to enhance affinity and selectivity for sensing of airborne analytes. In this Account, the contributions from our lab on porous organic cages are presented.

Post-Assembly Reactivity of N-Aryl Iminoboronates: Reversible Radical Coupling and Unusual B-N Dynamic Covalent Chemistry

Post-assembly reaction of a dynamic covalent iminoboronate system following addition of Cp2 Co resulted in the formation of a series of new reductively coupled dianionic dimers via C-C bond formation. The dimers formed as a mixture of BN-containing isomeric products: diastereomers rac5 and meso5, with coupled five-membered rings, and enantiomeric rac6, with a fused six-membered ring bicyclic system from C-C bond formation and rearrangement of the B-N bonds. Each isomer was identified using 1 H NMR spectroscopy in combination with single crystal X-ray structure determination. Interestingly, interconversion between the coupled five-membered rings (rac5 ) and fused bicyclic systems (rac6 ) was found to occur through an unprecedented breaking and reforming of the B-N covalent bond. Further, the coupled products could be converted quantitatively back to their iminoboronate precursors with addition of the electron abstractor Ph3 C+ .

High-throughput discovery of organic cages and catenanes using computational screening fused with robotic synthesis

Supramolecular synthesis is a powerful strategy for assembling complex molecules, but to do this by targeted design is challenging. This is because multicomponent assembly reactions have the potential to form a wide variety of products. High-throughput screening can explore a broad synthetic space, but this is inefficient and inelegant when applied blindly. Here we fuse computation with robotic synthesis to create a hybrid discovery workflow for discovering new organic cage molecules, and by extension, other supramolecular systems. A total of 78 precursor combinations were investigated by computation and experiment, leading to 33 cages that were formed cleanly in one-pot syntheses. Comparison of calculations with experimental outcomes across this broad library shows that computation has the power to focus experiments, for example by identifying linkers that are less likely to be reliable for cage formation. Screening also led to the unplanned discovery of a new cage topology-doubly bridged, triply interlocked cage catenanes.

Networked Cages for Enhanced CO2 Capture and Sensing

It remains a great challenge to design and synthesize a porous material for CO2 capture and sensing simultaneously. Herein, strategy of "cage to frameworks" is demonstrated to synthesize fluorescent porous organic polymer (pTOC) by using tetraphenylethylene-based oxacalixarene cage (TOC) as the monomer. The networked cages (pTOC) have improved porous properties, including Brunauer-Emmett-Teller surface area and CO2 capture compared with its monomer TOC, because the polymerization overcomes the window-to-arene packing modes of cages and turns on their pores. Moreover, pTOC displays prominent reversible fluorescence enhancement in the presence of CO2 in different dispersion systems and fluorescence recovery for CO2 release in the presence of NH3·H2O, and is thus very effective to detect and quantify the fractions of CO2 in a gaseous mixtures.

Hierarchical Assembly of an Interlocked M8 L16 Container

The self-assembly of eight PdII cations and sixteen phenanthrene-derived bridging ligands with 60° bite angles yielded a novel M8 L16 metallosupramolecular architecture composed of two interlocked D4h -symmetric barrel-shaped containers. Mass spectrometry, NMR spectroscopy, and X-ray analysis revealed this self-assembled structure to be a very large "Hopf link" catenane featuring channel-like cavities, which are occupied by NO3- anions. The importance of the anions as catenation templates became imminent when we observed the nitrate-triggered structural rearrangement of a mixture of M3 L6 and M4 L8 assemblies formed in the presence of BF4- anions into the same interlocked molecule. Furthermore, the densely packed structure of the M8 L16 catenane was exploited in the preparation of a hexyloxy-functionalized analogue, which further self-assembled into vesicle-like aggregates in a reversible manner.

Template-Directed Synthesis of a Conjugated Zinc Porphyrin Nanoball

We report the template-directed synthesis of a π-conjugated 14-porphyrin nanoball. This structure consists of two intersecting nanorings containing six and 10 porphyrin units. Fluorescence upconversion spectroscopy experiments demonstrate that electronic excitation delocalizes over the whole three-dimensional π system in less than 0.3 ps if the nanoball is bound to its templates or over 2 ps if the nanoball is empty.

Dynamic Interconversion between Boroxine Cages Based on Pyridine Ligation

Dynamic interconversion between large covalent organic cages was achieved simply by heating or acid/base treatment. A mixture of the boroxine cages 12-mer and 15-mer was cleanly converted into a pyridine adduct of the 9-mer boroxine cage upon treatment with pyridine, and the geometry of N-coordinated boron atoms changed from trigonal to tetrahedral. The reverse reaction was achieved by heating or acid treatment. In this process, the larger boroxine cages 12-mer and 15-mer were found to be entropically favored owing to the release of free pyridine molecules from 9-mer⋅6 Py.

Regiochemical Control in Triptycene Formation-An Exercise in Subtle Balancing Multiple Factors

Reactions between 1,8‐dichloroanthracenes with substituents in position 10 and ortho‐chloroaryne afford mixtures of 1,8,13‐ (syn) and 1,8,16‐trichlorotriptycenes (anti). The syn/anti ratio is dependent on these substituents. Electropositive substituents like SiMe₃ and GeMe₃ lead to preferred formation of the syn‐isomer, whereas CMe₃ groups exclusively afford the anti‐isomer. Different quantum chemical calculations including location of transition states give conflicting results, but indicate the importance of dispersion forces for an at least qualitative prediction of results. The syn‐trichlorotriptycenes with SiMe₃ and GeMe₃ substituents were characterized by using NMR spectroscopy, mass spectrometry, and X‐ray diffraction experiments.

Temperature-dependent self-assembly of a purely organic cage in water

Using a novel dynamic covalent approach relying on reversible hydrazone formation, a purely organic 3-dimensional prismatic cage was developed in water at elevated temperatures.

Precursor control over the self-assembly of [2]catenanes via hydrazone condensation in water

By means of hydrazone condensation, a series of homo-[2]catenanes were self-assembled in high yields in water.

Porous Molecular Solids and Liquids

Until recently, porous molecular solids were isolated curiosities with properties that were eclipsed by porous frameworks, such as metal-organic frameworks. Now molecules have emerged as a functional materials platform that can have high levels of porosity, good chemical stability, and, uniquely, solution processability. The lack of intermolecular bonding in these materials has also led to new, counterintuitive states of matter, such as porous liquids. Our ability to design these materials has improved significantly due to advances in computational prediction methods.

Selective C70 encapsulation by a robust octameric nanospheroid held together by 48 cooperative hydrogen bonds

Self-assembly of multiple building blocks via hydrogen bonds into well-defined nanoconstructs with selective binding function remains one of the foremost challenges in supramolecular chemistry. Here, we report the discovery of a enantiopure nanocapsule that is formed through the self-assembly of eight amino acid functionalised molecules in nonpolar solvents through 48 hydrogen bonds. The nanocapsule is remarkably robust, being stable at low and high temperatures, and in the presence of base, presumably due to the co-operative geometry of the hydrogen bonding motif. Thanks to small pore sizes, large internal cavity and sufficient dynamicity, the nanocapsule is able to recognize and encapsulate large aromatic guests such as fullerenes C₆₀ and C₇₀. The structural and electronic complementary between the host and C₇₀ leads to its preferential and selective binding from a mixture of C₆₀ and C₇₀.

Individual hydrogen bonds are weak, so self-assembling multiple components via hydrogen bonding is a significant challenge. Here the authors report a robust, enantiopure nanocapsule held together by 48 cooperative hydrogen bonds, and use it for the selective binding of C₇₀.

Topological landscapes of porous organic cages

We define a nomenclature for the classification of porous organic cage molecules, enumerating the 20 most probable topologies, 12 of which have been synthetically realised to date. We then discuss the computational challenges encountered when trying to predict the most likely topological outcomes from dynamic covalent chemistry (DCC) reactions of organic building blocks. This allows us to explore the extent to which comparing the internal energies of possible reaction outcomes is successful in predicting the topology for a series of 10 different building block combinations.

PdII2L4-type coordination cages up to three nanometers in size

The utilization of large ligands in coordination-based self-assembly represents an attractive strategy for the construction of supramolecular assemblies more than two nanometers in size. However, the implementation of this strategy is hampered by the fact that the preparation of such ligands often requires substantial synthetic effort. Herein, we describe a simple one-step protocol, which allows large bipyridyl ligands with a bent shape to be synthesized from easily accessible and/or commercially available starting materials. The ligands were used to construct PdII2L4-type coordination cages of unprecedented size. Furthermore, we provide evidence that these cages may be stabilized by close intramolecular packing of lipophilic ligand side chains. Packing effects of this kind are frequently encountered in protein assemblies, but they are seldom used as a design element in metallasupramolecular chemistry.

A Perspective on the Synthesis, Purification, and Characterization of Porous Organic Cages

Porous organic cages present many opportunities in functional materials chemistry, but the synthetic challenges for these molecular solids are somewhat different from those faced in the areas of metal-organic frameworks, covalent-organic frameworks, or porous polymer networks. Here, we highlight the practical methods that we have developed for the design, synthesis, and characterization of imine porous organic cages using CC1 and CC3 as examples. The key points are transferable to other cages, and this perspective should serve as a practical guide to researchers who are new to this field.

Chiral triptycene-pyrene π-conjugated chromophores with circularly polarized luminescence

Novel chiral triptycenes showing circularly polarized luminescence based on the supramolecular chirality induced in the hydrogen-bonded aggregate have been developed.

Modular assembly of porous organic cage crystals: isoreticular quasiracemates and ternary co-crystal

Co-crystallisation of helically chiral porous organic cage molecules has enabled the formation of isoreticular quasiracemates and a rare porous organic ternary co-crystal.