Applications of macrocycle-based solid-state host-guest chemistry

Boat-to-boat conformation inversions of cyclobis[7,8-(para-quinodimethane)-3,7-(9-(p-tolyl)-9H-carbazole)] in the neutral and tetracationic state

We report the synthesis of macrocyclic cyclobis[7,8-(para-quinodimethane)-3,7-(9-(p-tolyl)-9H-carbazole)] CBQCz. We found that CBQCz showed temperature-dependent and four-electron oxidative conformation changes. Both CBQCz and CBQCz4+ possess boat-to-boat conformation inversions. The smaller inverted energy and less curved structure of CBQCz4+ are due to the conjugated effect of tetracations.

Supramolecular-macrocycle-based functional organic cocrystals

Supramolecular macrocycles, renowned for their remarkable capabilities in molecular recognition and complexation, have emerged as pivotal elements driving advancements across various innovative research fields. Cocrystal materials, an important branch within the realm of crystalline organic materials, have garnered considerable attention owing to their simple preparation methods and diverse potential applications, particularly in optics, electronics, chemical sensing and photothermal conversion. In recent years, macrocyclic entitles have been successfully brought into this field, providing an essential and complementary channel to create novel functional materials, especially those with multiple functionalities and smart stimuli-responsiveness. In this Review, we present an overview of the research efforts on functional cocrystals constructed with macrocycles, covering their design principles, preparation strategies, assembly modes, and diverse functions and applications. Finally, the remaining challenges and perspectives are outlined. We anticipate that this review will serve as a valuable and timely reference for researchers interested in supramolecular crystalline materials and beyond, catalyzing the emergence of more original and innovative studies in related fields.

Guest-Induced Conformational Transformations in Tiara[5]arene Crystals: A Pathway for Molecular Sieving

In pursuit of environmental sustainability and energy efficiency, assorted macrocyclic compounds have recently emerged as crystalline adsorbents for the efficient molecular sieving of various chemical commodities. Herein, we delve into the conformational characteristics and solid-state packing modes of tiara[5]arenes (T[5]), a rim-differentiated pillar[5]arene derivative. By meticulously exploring the conformational space, we have successfully identified a multitude of distinct T[5] conformers within a relatively narrow energy range of 22 kJ/mol. This finding underscores the inherent conformational flexibility of this macrocyclic scaffold, enabling T[5] to adapt diverse packing arrangements in the solid state. While solvent-free T[5] crystals do not exhibit permanent porosity, they undergo solvomorphic interconversions when exposed to various guest compounds. Our study demonstrates that T[5]-based crystalline materials exhibit a notable preference for selectively capturing aromatic and olefinic solvents, such as benzene, toluene, chlorobenzene, and cyclohexene, over their aliphatic hydrocarbon counterparts from equivalent volume liquid mixtures, achieving up to 10:1 selectivity between benzene and cyclohexane.

Supramolecular Assembly of Fused Macrocycle-Cage Molecules for Fast Lithium-Ion Transport

We report a new supramolecular porous crystal assembled from fused macrocycle-cage molecules. The molecule comprises a prismatic cage with three macrocycles radially attached. The molecules form a nanoporous crystal with one-dimensional (1D) nanochannels. The supramolecular porous crystal can take up lithium-ion electrolytes and achieve an ionic conductivity of up to 8.3 × 10-4 S/cm. Structural analysis and density functional theory calculations reveal that efficient Li-ion electrolyte uptake, the presence of 1D nanochannels, and weak interactions between lithium ions and the crystal enable fast lithium-ion transport. Our findings demonstrate the potential of fused macrocycle-cage molecules as a new design motif for ion-conducting molecular crystals.

An anthracene-containing crown ether: synthesis, host-guest properties and modulation of solid state luminescence

Organic solid state vapochromic materials are of great significance for the development of supramolecular chemistry and materials science. Herein, we synthesize a crown ether derivative (An34C10) containing two anthracene units and construct new crown ether-based vapochromic host-guest co-crystals. Due to the presence of anthracene, An34C10 not only shows good fluorescence properties but also displays mechanochromism. Single crystal structural analysis, powder X-ray diffraction and differential scanning calorimetry experiments demonstrate that the transformation between different stacking modes of An34C10 is responsible for mechanochromism. In addition, An34C10 can complex with 1,2,4,5-tetracyanobenzene (TCNB) to form host-guest complex (An34C10@TCNB) co-crystals. Because organic solvent fuming alters charge-transfer interactions in An34C10@TCNB, the fluorescence of the co-crystals can be turned on and off by 4-methylpyridine and chloroform vapors, respectively, realizing selective detection with opposite emission outputs. Meanwhile, the stimuli-responsive properties of An34C10 and An34C10@TCNB possess good cycling performance. This work provides a new strategy for the construction of organic solid state luminescent materials.

Supramolecular light-harvesting systems utilizing tetraphenylethylene chromophores as antennas

Efficient utilization of light energy is crucial for various technological applications ranging from solar energy conversion to optoelectronic devices. Supramolecular light-harvesting systems (LHS) have emerged as promising platforms for enhancing light absorption and energy transfer process. In this Feature Article, we highlight the utilization of tetraphenylethylene (TPE) chromophores as antennas in supramolecular assemblies for light harvesting applications. TPE, as an archetypal aggregation-induced emission (AIE) chromophore, offers unique advantages such as high photostability and efficient light-harvesting capabilities upon self-assembly. We discuss the design principles and synthetic strategies employed to construct supramolecular assemblies incorporating TPE chromophores, elucidating their roles as efficient light-harvesting antennas. Furthermore, we delve into the mechanisms governing energy transfer processes within these assemblies, such as Förster resonance energy transfer (FRET). The potential applications of these TPE-based supramolecular systems in various fields, including photocatalysis, reactive oxygen species generation, optoelectronic devices and sensing, are explored. Finally, we provide insights into future directions and challenges in the development of next-generation supramolecular LHSs utilizing TPE chromophores.

Encapsulated TADF macrocycles for high-efficiency solution-processed and flexible organic light-emitting diodes

Macrocyclic thermally activated delayed fluorescence (TADF) emitters have been demonstrated to realize high efficiency OLEDs, but the design concept was still confined to rigid π-conjugated structures. In this work, two macrocyclic TADF emitters, Cy-BNFu and CyEn-BNFu, with a flexible alkyl chain as a linker and bulky aromatic hydrocarbon wrapping units were designed and synthesized. The detailed photophysical analysis demonstrates that the flexible linker significantly enhances the solution-processibility and flexibility of the parent TADF core without sacrificing the radiative transition and high PLQY. Moreover, benefiting from sufficient encapsulation of both horizontal and vertical space, the macrocyclic CyEn-BNFu further isolated the TADF core and inhibited the aggregation caused quenching, which benefits the utilization of triplet excitons. As a result, the non-doped solution-processed OLEDs based on CyEn-BNFu exhibit high maximum external quantum efficiencies (EQE) up to 32.3%, which were 3 times higher than those of the devices based on the parent molecule. In particular, these macrocyclic TADF emitters ensure the fabrication of flexible OLEDs with higher brightness, color purity and bending resistance. This work opens a way to construct macrocyclic TADF emitters with a flexible alkyl chain linker and highlights the benefits of such encapsulated macrocycles for optimizing the performance of flexible solution-processed devices.

Deep-Cavity Calix[4]naphth[4]arene Macrocycles: Synthesis, Conformational Features, and Solid-State Structures

We recently introduced calix[n]naphth[m]arenes as a novel class of deep-cavity hybrid macrocycles constituted by phenol (n) and naphthalene (m) units. In this study, we report the synthesis, conformational analysis, spectroscopic properties, and solid-state structures of calix[4]naphth[4]arene (C4N4) and its permethylated analog (C4N4-Me), thereby expanding the calix[n]naphth[m]arene family. C4N4 was synthesized through a 2 + 2 fragment coupling macrocyclization under acidic conditions, where the solvent played a crucial role in selectively forming the C4N4 derivative. The X-ray structure of C4N4 reveals a chair-like 1,2,3,4-alternate conformation characterized by two opposing 3/4-cone moieties stabilized by intramolecular hydrogen bonds. In contrast, the X-ray structure of C4N4-Me exhibits a 1,3,5,7-alternate conformation.

A Pillar[5]arene-Containing Metal-Organic Framework for Rapid and Highly Capable Adsorption of a Mustard Gas Simulant

Mustard gas causes irreversible damage upon inhalation or contact with the human body. Consequently, the development of adsorbents for effective interception of mustard gas at low concentrations and high flow rates is an urgent necessity. Here we report a stable porous pillar[5]arene-containing metal-organic framework (MOF) based on zirconium (EtP5-Zr-scu), demonstrating that embedding pillar[5]arene units in MOFs can provide specific binding sites for efficient adsorption of a mustard gas simulant, 2-chloroethyl ethyl sulfide (CEES). EtP5-Zr-scu achieves a higher capacity and more rapid adsorption compared to its counterpart without embedded pillar[5]arene units (H4tcpt-Zr-scu) and perethylated pillar[5]arene (EtP5) alone. Single crystal X-ray diffraction and solid-state nuclear magnetic resonance reveal that the enhanced performance of EtP5-Zr-scu is derived from the host-guest complexation between CEES and pillar[5]arene moieties. Moreover, breakthrough experiments confirmed that the interception performance of EtP5-Zr-scu against CEES (800 ppm, 120 mL/min) was significantly improved (566 min/g) compared with H4tcpt-Zr-scu (353 min/g) and EtP5 (0.873 min/g), attributed to the integration of open channels with specific recognition sites. This work marks a significant advancement in the development of macrocycle-incorporated crystalline framework materials with recognition sites for the efficient capture of guest molecules.

Dynamic Gas-Bridged Bond: An Opportunity of Fabricating Dynamic Assembled Materials with Gas

Gas molecules, as a family of unique polyatomic building blocks, have long been considered hard to involve in molecular assembly or construct assembled materials due to their structural simplicity yet paucity of defined interacting sites. To solve this non-trivial challenge, a core idea is to break the limit of current ways of bonding gas molecules, endowing them with new modes of interactions that match the basic requirements of molecular assembly. In recent years, a new concept, named the dynamic gas-bridged bond (DGB), has emerged, which allows for gas molecules to constitute a dynamic bridging structure between other building blocks with the aid of frustrated Lewis pairs. This makes it possible to harness gas in a supramolecular or dynamic manner. Herein, this perspective discusses distinct dynamic natures of DGBs and manifests their particular functions in various fields, including the control of molecular/polymeric self-assembly nanostructures, creation of multidimensional assembled materials, and recyclable catalysts. The future research direction and challenges of dynamic gas-bridged chemistry toward gas-programmed self-assembly and gas-constructed adaptive materials are highlighted.

Laponite-activated AIE supramolecular assembly with modulating multicolor luminescence for logic digital encryption and perfluorinated pollutant detection

Recently, the non-covalently activated supramolecular scaffold method has become a prominent research area in the field of intelligent materials. Here, the inorganic clay (LP) promoted the AIE properties of 4,4',4″,4‴-(ethene-1,1,2,2-tetrayltetrakis(benzene-4,1-diyl))tetrakis(1-ethylpyridin-1-ium) (P-TPE), showing an astonishing 42-fold enhancement of the emission intensity of the yellow-green luminescence and a 34-fold increase of the quantum yield via organic-inorganic supramolecular strategy as well as the efficient light-harvesting properties (energy transfer efficiency up to 33 %) after doping with the dye receptor Rhodamine B. Furthermore, the full-color spectral regulation, including white light, was achieved by adjusting the ratio of the donor to the acceptor component and co-assembling with the carbon dots (CD). Interestingly, this TPE-based non-covalently activated full-color supramolecular light-harvesting system (LHS) could be achieved not only in aqueous media but also in the hydrogel and the solid state. More importantly, this panchromatic tunable supramolecular LHS exhibited the multi-mode and quadruple digital logic encryption property as well as the specific detection ability towards the perfluorobutyric acid and the perfluorobutanesulfonic acid, which are harmful to human health in drinking water. This result develops a simple, convenient and effective approach for the intelligent anti-counterfeiting and the pollutant sensing.

The effect of host size on binding in host-guest complexes of cyclodextrins and polyoxometalates

Harnessing flexible host cavities opens opportunities for the design of novel supramolecular architectures that accommodate nanosized guests. This research examines unprecedented gas-phase structures of Keggin-type polyoxometalate PW12O40 3- (WPOM) and cyclodextrins (X-CD, X = α, β, γ, δ, ε, ζ) including previously unexplored large, flexible CDs. Using ion mobility spectrometry coupled to mass spectrometry (IM-MS) in conjunction with molecular dynamics (MD) simulations, we provide first insights into the binding modes between WPOM and larger CD hosts as isolated structures. Notably, γ-CD forms two distinct structures with WPOM through binding to its primary and secondary faces. We also demonstrate that ε-CD forms a deep inclusion complex, which encapsulates WPOM within its annular inner cavity. In contrast, ζ-CD adopts a saddle-like conformation in its complex with WPOM, which resembles its free form in solution. More intriguingly, the gas-phase CD-WPOM structures are highly correlated with their counterparts in solution as characterized by nuclear magnetic resonance (NMR) spectroscopy. The strong correlation between the gas- and solution phase structures of CD-WPOM complexes highlight the power of gas-phase IM-MS for the structural characterization of supramolecular complexes with nanosized guests, which may be difficult to examine using conventional approaches.

One-Step Catalyst-Transfer Macrocyclization: Expanding the Chemical Space of Azaparacyclophanes

In this paper, we report on a one-step catalyst-transfer macrocyclization (CTM) reaction, based on the Pd-catalyzed Buchwald-Hartwig cross-coupling reaction, selectively affording only cyclic structures. This route offers a versatile and efficient approach to synthesize aza[1n]paracyclophanes (APCs) featuring diverse functionalities and lumens. The method operates at mild reaction temperatures (40 °C) and short reaction times (∼2 h), delivering excellent isolated yields (>75% macrocycles) and up to 30% of a 6-membered cyclophane, all under nonhigh-dilution concentrations (35-350 mM). Structural insights into APCs reveal variations in product distribution based on different endocyclic substituents, with steric properties of exocyclic substituents having minimal influence on the macrocyclization. Aryl-type endocyclic substituents predominantly yield 6-membered macrocycles, while polycyclic aromatic units such as fluorene and carbazole favor 4-membered species. Experimental and computational studies support a proposed mechanism of ring-walking catalyst transfer that promotes the macrocycle formation. It has been found that the macrocyclization is driven by the formation of cyclic conformers during the oligomerization step favoring an intramolecular C-N bond formation that, depending on the cycle size, hinges on either preorganization effect or kinetic increase of the reductive elimination step or a combination of the two. The CTM process exhibits a "living" behavior, facilitating sequential synthesis of other macrocycles by introducing relevant monomers, thus providing a practical synthetic platform for chemical libraries. Notably, CTM operates both under diluted and concentrated regimes, offering scalability potential, unlike typical macrocyclization reactions usually operating in the 0.1-1 mM range.

A supramolecular electrochemical probe based on a tetrazole derivative pillar[5]arene/methylene blue system

For the first time, an original synthetic approach has been developed that enables the introduce ten tetrazole fragments into the pillar[5]arene structure. A supramolecular electrochemical probe was assembled for the first time from the obtained macrocycles and an electrochemically active signal converter: methylene blue (MB) dye. The ability of pillar[5]arene containing tetrazole fragments to selectively bind MB was confirmed by UV-vis and 2D 1H-1H NOESY spectroscopy. The stoichiometry of the resulting pillar[5]arene/MB complex = 1 : 2. This new supramolecular probe pillar[5]arene/MB allowed the detection of changes in the electrochemical signals of MB implemented in the supramolecular complex depending on the presence or absence of some metal ions (Zn2+ and Co2+) that do not exert their own redox activity. This will find further applications for the enhancement of the range of analytes detected by their influence on host-guest complexation and for the design of biosensors based on specific DNA-MB interactions.

Incorporation of an Anion-Coordinated Triple Helicate into a Thin Film for Choline Recognition in an Aqueous System

Functional thin films, being fabricated by incorporating discrete supramolecular architectures, have potential applications in research areas such as sensing, energy storage, catalysis, and optoelectronics. Here, we have determined that an anion-coordinated triple helicate can be solution-processed into a functional thin film by incorporation into a polymethyl methacrylate (PMMA) matrix. The thin films fabricated by the incorporation of the anion-coordinated triple helicate show multiple optical properties, such as fluorescence, CD, and CPL. In addition, the film has the ability to recognize choline and choline derivatives in a water system. The successful recognition of Ch+ by the film represents the first example of utilizing 'aniono'-supramolecular architectures for biomolecule detection in aqueous solution and opens up a new route for designing biocompatible functional materials.

Halogen-Bonded Supramolecular Parallelograms: From Self-Complementary Iodoalkyne Halogen-Bonded Dimers to 1:1 and 2:2 Iodoalkyne Halogen-Bonded Cocrystals

The formation of supramolecular parallelograms utilizing iodoalkyne-pyridine halogen bonding is described. The crystal structures of four iodoalkynyl-substituted (phenylethynyl)pyridines demonstrate the feasibility of discrete self-complementary dimer formation. These compounds 3-(2-iodoethynyl-phenylethynyl) pyridine (1), 2-(3-iodoethynyl-phenylethynyl) pyridine (2), 3-(4,5-difluoro-2-iodoethynyl-phenylethynyl) pyridine (3), and 2-(5-iodoethynyl-2,4-dimethylphenylethynyl) pyridine (4) all form parallelogram-shaped dimers with two self-complementary short N-I halogen bonds. The potential formation of iodoalkynyl halogen-bonded supramolecular macrocycles is demonstrated by the formation of a discrete halogen-bonded parallelogram-shaped complex in the 1:1 cocrystal formed from the bis iodoalkyne, 1-iodoethynyl-2-(3-iodoethynyl-phenylethynyl)-4,5-dimethoxybenzene (6), and the dipyridyl, 5-phenyl-2-(pyridin-3-ylethynyl)pyridine (7). Furthermore, discrete supramolecular parallelograms form within the 2:2 cocrystal formed between 1,2-bis(iodoethynyl)-4,5-difluorobenzene and the dipyridyl 4-(3-pyridylethynyl) pyridine (8).