Alkyl Chain Length-Selective Vapor-Induced Fluorochromism of Pillar[5]arene-Based Nonporous Adaptive Crystals

Macrocycle-Based Charge Transfer Cocrystals with Dynamically Reversible Chiral Self-Sorting Display Chain Length-Selective Vapochromism to Alkyl Ketones

Chirality-driven self-sorting plays an essential role in controlling the biofunction of biosystems, such as the chiral double-helix structure of DNA from self-recognition by hydrogen bonding. However, achieving precise control over the chiral self-sorted structures and their functional properties for the bioinspired supramolecular systems still remains a challenge, not to mention realizing dynamically reversible regulation. Herein, we report an unprecedented saucer[4]arene-based charge transfer (CT) cocrystal system with dynamically reversible chiral self-sorting synergistically induced by chiral triangular macrocycle and organic vapors. It displays efficient chain length-selective vapochromism toward alkyl ketones due to precise modulation of optical properties by vapor-induced diverse structural transformations. Experimental and theoretical studies reveal that the unique vapochromic behavior is mainly attributed to the formation of homo- or heterochiral self-sorted assemblies with different alkyl ketone guests, which differ dramatically in solid-state superstructures and CT interactions, thus influencing their optical properties. This work highlights the essential role of chiral self-sorting in controlling the functional properties of synthetic supramolecular systems, and the rarely seen controllable chiral self-sorting at the solid-vapor interface deepens the understanding of efficient vapochromic sensors.

Optical Phenomena in Molecule-Based Magnetic Materials

Since the last century, we have witnessed the development of molecular magnetism which deals with magnetic materials based on molecular species, i.e., organic radicals and metal complexes. Among them, the broadest attention was devoted to molecule-based ferro-/ferrimagnets, spin transition materials, including those exploring electron transfer, molecular nanomagnets, such as single-molecule magnets (SMMs), molecular qubits, and stimuli-responsive magnetic materials. Their physical properties open the application horizons in sensors, data storage, spintronics, and quantum computation. It was found that various optical phenomena, such as thermochromism, photoswitching of magnetic and optical characteristics, luminescence, nonlinear optical and chiroptical effects, as well as optical responsivity to external stimuli, can be implemented into molecule-based magnetic materials. Moreover, the fruitful interactions of these optical effects with magnetism in molecule-based materials can provide new physical cross-effects and multifunctionality, enriching the applications in optical, electronic, and magnetic devices. This Review aims to show the scope of optical phenomena generated in molecule-based magnetic materials, including the recent advances in such areas as high-temperature photomagnetism, optical thermometry utilizing SMMs, optical addressability of molecular qubits, magneto-chiral dichroism, and opto-magneto-electric multifunctionality. These findings are discussed in the context of the types of optical phenomena accessible for various classes of molecule-based magnetic materials.

Silapillar[n]arenes: Their Enhanced Electronic Conjugation and Conformational Versatility

During recent decades, methylene-bridged macrocyclic arenes have been widely used in supramolecular chemistry. However, their π-conjugations are very weak, as the methylene bridges disrupt the electronic communication between π orbitals of the aromatic units. Herein, we successfully synthesized a series of silapillar[n]arenes (n = 4, 6, and 8) using silylene bridging. These showed enhanced electronic conjugation compared with the parent pillar[n]arenes because of σ*-π* conjugation between σ* (Si-C) orbitals and π* orbitals of the benzenes. Owing to the longer Si-C bond compared with the C-C bond, silylene-bridging provides additional structural flexibility into the pillar[n]arene scaffolds; a strained silapillar[4]arene was formed, which is unavailable in the parent pillar[n]arenes because of the steric requirements. Furthermore, silapillar[n]arenes displayed interesting size-dependent structural and optical properties.

Stimuli-fluorochromic smart organic materials

Smart materials based on stimuli-fluorochromic π-conjugated solids (SFCSs) have aroused significant interest due to their versatile and exciting properties, leading to advanced applications. In this review, we highlight the recent developments in SFCS-based smart materials, expanding beyond organometallic compounds and light-responsive organic luminescent materials, with a discussion on the design strategies, exciting properties and stimuli-fluorochromic mechanisms along with their potential applications in the exciting fields of encryption, sensors, data storage, display, green printing, etc. The review comprehensively covers single-component and multi-component SFCSs as well as their stimuli-fluorochromic behaviors under external stimuli. We also provide insights into current achievements, limitations, and major challenges as well as future opportunities, aiming to inspire further investigation in this field in the near future. We expect this review to inspire more innovative research on SFCSs and their advanced applications so as to promote further development of smart materials and devices.

Structure-activity strategies for mechanically responsive fluorescent materials: a molecular perspective

Mechanical response luminescence (MRL) describes the photophysical properties triggered by mechanical stimulation. Usually, MRL can be regulated by intermolecular interactions, molecular conformation or molecular packing, to achieve the desirable optical properties. Herein, at the molecular level, this review covers the factors that influence mechanically responsive fluorescent materials, involving the single- or multifactorial modulation of aliphatic chains, donor-receptor switch, substituent adjustment, and position isomerism. According to these factors, the structure-activity strategies can be summarized as: (i) the self-recovery of optical properties, from the final to initial state, can be regulated by introducing long alkyl chains to a fluorophore. (ii) The sensitivity of MRL materials can be controlled by modifying the donor-acceptor structure via the changed ICT (intramolecular charge transfer) and intramolecular interaction. (iii) The electronic and steric effects of substituents can affect ICT and intermolecular interactions, thereby resulting in high quantum yield and high-contrast MRL materials via changing the molecular stacking of crystalline states. (iv) Intermolecular interaction is modulated by the position isomerism of the substituents, which results in switched molecular packing for the extended response toward a wide range of stimuli. It is anticipated that the molecular mechanisms of these structure-activity relationships will serve as a significant reference for developing novel, high contrast, recyclable mechanical response luminous materials.

Stimuli-Responsive Properties on a Bisbenzofuropyrazine Core: Mechanochromism and Concentration-Controlled Vapochromism

Stimulus-responsive organic materials with luminescence switching properties have attracted considerable attention for their practical applications in sensing, security, and display devices. In this paper, bent-type bisbenzofuropyrazine derivatives, Bent-H and Bent-sBu, with good solubilities were synthesized, and their physical and optical properties were investigated in detail. Bent-H gave three crystalline polymorphs, and they showed different luminescence properties depending on their crystal packing structures. In addition, Bent-H exhibited mechanochromic luminescence in spite of its rigid skeleton. Bent-sBu exhibited unique concentration-dependent vapochromic luminescence. Ground Bent-sBu was converted to blue-emissive, green-emissive, and green-emissive high-viscosity solution states at low, moderate, and high concentrations of CHCl3 vapor, respectively. This finding represents a concentration-dependent multi-phase transition with an organic solvent, which is of potent interest for application in sensing systems.

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

Macrocyclic molecules have been used in various fields owing to their guest binding properties. Macrocycle-based host-guest chemistry in solution can allow for precise control of complex formation. Although solution-phase host-guest complexes are easily prepared, their limited stability and processability prevent widespread application. Extending host-guest chemistry from solution to the solid state results in complexes that are generally more robust, enabling easier processing and broadened applications. Macrocyclic compounds in the solid state can encapsulate guests with larger affinities than their soluble counterparts. This is crucial for use in applications such as separation science and devices. In this Review, we summarize recent progress in macrocycle-based solid-state host-guest chemistry and discuss the basic physical chemistry of these complexes. Representative macrocycles and their solid-state complexes are explored, as well as potential applications. Finally, perspectives and challenges are discussed.

A Nitro-Modified Luminescent Hydrogen-Bonded Organic Framework for Non-Contact and High-Contrast Sensing of Aromatic Amines

The global demand for intelligent sensing of aromatic amines has consistently increased due to concerns about health and the environment. Efforts to improve material design and understand mechanisms have been made, but highly efficient non-contact sensing with host-guest structures remains a challenge. Herein, we report the first example of non-contact, high-contrast sensing of aromatic amines in a hydrogen-bonded organic framework (HOF) based on a nitro-modified stereo building block. Direct observation of binding interactions of trapped amines is achieved, leading to charge separation-induced emission quenching between host and guests. Non-contact sensing of aniline and diphenylamine is realized with quenching efficiencies up to 91.7 % and 97.0 %, which shows potential for versatile applications. This work provides an inspiring avenue to engineer multifunctional HOFs via co-crystal preparations, thus enriching applications of porous materials with explicit mechanisms.

Smart organic materials based on macrocycle hosts

Innovative design of smart organic materials is of great importance for the advancement of modern technology. Macrocycle hosts, possessing cyclic skeletons, intrinsic cavities, and specific guest binding properties, have demonstrated pronounced potential for the elaborate fabrication of a variety of functional organic materials with smart stimuli-responsive characteristics. In this tutorial review, we outline the current development of smart organic materials based on macrocycle hosts as key building blocks, focusing on the design principles and functional mechanisms of the tailored systems. Three main types of macrocycle-based smart organic materials are exemplified as follows according to the distinct forms of construction patterns: (1) supramolecular polymeric materials and nanoassemblies; (2) adaptive molecular crystals; (3) smart porous organic materials. The responsive performances of macrocycle-containing smart materials in versatile aspects, including mechanically adaptive polymers, soft optoelectronic devices, data encryption, drug delivery systems, artificial transmembrane channels, crystalline-state gas adsorption/separation, and fluorescence sensing, are illustrated by discussing the representative studies as paradigms, where the roles of macrocycles in these systems are highlighted. We also provide in the conclusion part the perspectives and remaining challenges in this burgeoning field.

Efficient separation of monobromotoluene isomers by nonporous adaptive perbromoethylated pillar[5]arene crystals

Herein we report an efficient adsorptive separation approach for monobromotoluene isomers using nonporous adaptive crystals of perbromoethylated pillar[5]arene (BrP5). The purity of separated m-bromotoluene from an equal volume mixture of m-bromotoluene and o-bromotoluene reaches 96.6% in one cycle and the adsorbent BrP5 can be reused without losing separation performance.

Time-Dependent Solvent-Driven Solid-State Fluorescence-based Numeric Coding

Controllable solid-state transformations can provide a basis for novel functional materials. Herein, we report a series of solid-state systems that can be readily transformed between amorphous, co-crystalline, and mixed crystalline states via grinding or exposure to solvent vapors. The present solid materials were constructed using an all-hydrocarbon macrocycle, cyclo[8](1,3-(4,6-dimethyl)benzene) (D_4d-CDMB-8) (host), and neutral aggregation-caused quenching dyes (guests), including 9,10-dibromoanthracene (1), 1,8-naphtholactam (2), diisobutyl perylene-3,9-dicarboxylate (3), 4,4-difluoro-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene (4), 4,7-di(2-thienyl)-benzo[2,1,3]thiadiazole (5), and 4-imino-3-(pyridin-2-yl)-4H-quinolizine-1-carbonitrile (6). Seven co-crystals and six amorphous materials were obtained via host-guest complexation. Most of these materials displayed turn-on fluorescence emission (up to 20-fold enhancement relative to the corresponding solid-state guests). The interconversion between amorphous, co-crystalline states, and crystalline mixtures could be induced by exposure to solvent vapors or by subjecting to grinding. The transformations could be monitored readily by means of single-crystal and powder X-ray diffraction analyses, as well as solid-state fluorescent emission spectroscopy. The externally induced structural interconversions resulted in time-dependent fluorescence changes. This allowed sets of privileged number array codes to be generated.

Substrate-Responsive Pillar[5]arene-Based Organic Room-Temperature Phosphorescence

Room-temperature phosphorescence (RTP) is a photophysical phenomenon typically associated with a long-lived emission that can be detected by the unaided eye. Several natural proteins display RTP, as do certain artificial polymers. In both cases, the RTP is ascribed to effective intramolecular through-space electronic communication. However, small molecules with internal electronic communication that enable RTP are relatively rare. Herein, we describe an alkyl halide-responsive RTP system consisting of a meta-formylphenyl-bearing pillar[5]arene derivative that supports effective through-space charge transfer (TSCT) within the pillararene cavity. Treatment with bromoethane, a heavy atom-containing guest for the pillar[5]arene host, serves to enhance the emission. An isomeric para-formylphenyl-bearing pillar[5]arene system proved ineffective in producing an RTP effect. Quantum chemical calculations based on single-crystal X-ray diffraction analyses provided insights into the structural determinants governing TSCT between the 1,4-dimethoxybenzene donor units and the formylphenyl groups of the pillar[5]arene, as well as the associated energy gaps and intersystem crossing channels. We believe that the present system and the associated mechanistic analysis provide the foundation for design of new small molecule with tunable RTP features.

Covalently bridged pillararene-based polymers: structures, synthesis, and applications

Covalently bridged pillararene-based polymers (CBPPs) are a special class of macrocycle-based polymers in which multiple pillararene monomers are attached to the polymer structures by covalent bonds. Owing to the unique molecular structures including the connection components or the spatial structures, CBPPs have become increasingly popular in applications ranging from environmental science to biomedical science. In this review, CBPPs are divided into three types (linear polymers, grafted polymers, and cross-linked polymers) according to their structural characteristics and described from the perspective of synthesis methods comprehensively. In addition, the applications of CBPPs are presented, including selective adsorption and separation, fluorescence sensing and detection, construction of supramolecular gels, anticancer drug delivery, artificial light-harvesting, catalysis, and others. Finally, the current challenging issues and comprehensive prospects of CBPPs are discussed.

Efficient Purification of 2,6-Lutidine by Nonporous Adaptive Crystals of Pillararenes

2,6-Lutidine (2,6-LT) is a very important raw material in the chemical industry, but the impurities of 3-picoline (3-PC) and 4-picoline (4-PC) existing in 2,6-LT seriously affect its quality. Considering different molecular sizes of these three compounds, herein, we exploit nonporous adaptive crystals (NACs) of pillararenes as purifying agents for removal of 3-PC and 4-PC in 2,6-LT. We find that per-ethylated pillar[5]arene (EtP5) can selectively adsorb 3-PC and 4-PC, while negligible capture of 2,6-LT is observed, resulting in improvement of the purity of 2,6-LT up to 94.9%. Single-crystal structures indicate that the excellent selectivity originates from the size match and complexation stability differences among different host/guest pairs. After purification, NACs of EtP5 can be easily regenerated and used in the next run without a significant performance degradation.

Enhancing Mechanical Performance of a Polymer Material by Incorporating Pillar[5]arene-Based Host–Guest Interactions

Polymer gels have been widely used in the field for tissue engineering, sensing, and drug delivery due to their excellent biocompatibility, hydrophilicity, and degradability. However, common polymer gels are easily deformed on account of their relatively weak mechanical properties, thereby hindering their application fields, as well as shortening their service life. The incorporation of reversible non-covalent bonds is capable of improving the mechanical properties of polymer gels. Thus, here, a poly(methyl methacrylate) polymer network was prepared by introducing host–guest interactions between pillar[5]arene and pyridine cation. Owing to the incorporated host–guest interactions, the modified polymer gels exhibited extraordinary mechanical properties according to the results of the tensile tests. In addition, the influence of the host–guest interaction on the mechanical properties of the gels was also proved by rheological experiments and swelling experiments.

A Fluorescent Linear Conjugated Polymer Constructed from Pillararene and Anthracene

Over the past few years, conjugated polymers (CPs) have aroused much attention owing to their rigid conjugated structures, which can perform well in light harvesting and energy transfer and offer great potential in materials chemistry. In this article, we fabricate a new luminescent linear CP p(P[5](OTf)₂-co-9,10-dea) via the Sonogashira coupling of 9,10-diethynylanthracene and trifluoromethanesulfonic anhydride (OTf) modified pillar[5]arene, generating enhanced yellow-green fluorescence emission at around 552 nm. The reaction condition was screened to get a deeper understanding of this polymerization approach, resulting in an excellent yield as high as 92% ultimately. Besides the optical properties, self-assembly behaviors of the CP in low/high concentrations were studied, where interesting adjustable morphologies from tube to sheet were observed. In addition, the fluorescence performance and structural architecture can be disturbed by the host–guest reorganization between the host CP and the guest adiponitrile, suggesting great potential of this CP material in the field of sensing and detection.

Pillararene-Induced Intramolecular Through-Space Charge Transfer and Single-Molecule White-Light Emission

The fabrication of single-molecule white-light emission (SMWLE) materials has become a highly studied topic in recent years and through-space charge transfer (TSCT) is emerging as an important concept in this field. However, the preparation of ideal TSCT-based SMWLE materials is still a big challenge. Herein, we report a bifunctional pillar[5]arene (TPCN-P5-TPA) with a linear donor-spacer-acceptor structure and aggregation-induced emission (AIE) property. The bulky pillar[5]arene between the donor and acceptor induces a twisted conformation and a non-conjugated structure, resulting in intramolecular TSCT. In addition, the AIE feature and pillar[5]arene cavity endow TPCN-P5-TPA with responsiveness to viscosity and polar guests, by which the TSCT emission is triggered. The combination of blue locally-excited state emission and yellow TSCT emission of TPCN-P5-TPA generates SMWLE. Therefore, we provide a new and versatile strategy for the construction of TSCT-based SMWLE materials.

Thermo-Induced Fluorochromism in Two AIE Zinc Complexes: A Deep Insight into the Structure-Property Relationship

Solid-state emitters exhibiting mechano-fluorochromic or thermo-fluorochromic responses represent the foundation of smart tools for novel technological applications. Among fluorochromic (FC) materials, solid-state emissive coordination complexes offer a variety of fluorescence responses related to the dynamic of noncovalent metal-ligand coordination bonds. Relevant FC behaviour can result from the targeted choice of metal cation and ligands. Herein, we report the synthesis and characterization of two different colour emitters consisting of zinc complexes obtained from N,O bidentate ligands with different electron-withdrawing substituents. The two complexes are blue and orange solid-state fluorophores, respectively, highly responsive to thermal and mechanical stress. These emitters show a very different photoluminescent (PL) pattern as recorded before and after the annealing treatment. Through X-ray structural analysis combined with thermal analysis, infrared (IR) spectroscopy, PL, and DFT simulation we provide a comprehensive analysis of the structural feature involved in the fluorochromic response. Notably, we were able to correlate the on-off thermo-fluorochromism of the complexes with the structural rearrangement at the zinc coordination core.

Multistimuli-Responsive Squaraine Dyad Exhibiting Concentration-Controlled Vapochromic Luminescence

Stimuli-responsive organic materials with controllable luminescence are of enormous importance because of their potential applications in sensing, data security, and display devices. In this study, a multistimuli-responsive squaraine dyad (SQ-d) composed of two rigid squaraine moieties and a flexible ethylene linker was rationally designed and synthesized. SQ-d exhibits polymorphic luminescence, which can be reversibly switched by various external stimuli, including solvent vapor exposure, heat, and shear force. Unexpectedly, the weakly luminescent phase (O1) of SQ-d exhibits concentration-controlled vapochromic behavior. Film O1 can convert to a highly green-emissive phase (G1) under a low concentration of CHCl₃ vapor and convert to a highly yellow-emissive phase (Y) under a high concentration of CHCl₃ vapor; these originate from two distinct crystallization-induced emission enhancement processes. To the best of our knowledge, this is the first investigation of the effect of vapor concentration on the phase transitions of organic vapochromic luminophores. By analyzing the single-crystal structures and photophysical properties of SQ-d, we concluded that the green and yellow emissions probably originated from a zigzag stacking mode and an H-type π-π stacking mode, respectively. Finally, two prototypes based on SQ-d for applications in information encryption and vapor sensing were successfully demonstrated.

State- and water repellency-controllable molecular glass of pillar[5]arenes with fluoroalkyl groups by guest vapors

Molecular glasses are low-molecular-weight organic compounds that are stable in the amorphous state at room temperature. Herein, we report a state- and water repellency-controllable molecular glass by n-alkane guest vapors. We observed that a macrocyclic host compound pillar[5]arene with the C₂F₅ fluoroalkyl groups changes from the crystalline to the amorphous state (molecular glass) by heating above its melting point and then cooling to room temperature. The pillar[5]arene molecular glass shows reversible transitions between amorphous and crystalline states by uptake and release of the n-alkane guest vapors, respectively. Furthermore, the n-alkane guest vapor-induced reversible changes in the water contact angle were also observed: water contact angles increased and then reverted back to the original state by the uptake and release of the n-alkane guest vapors, respectively, along with the changes in the chemical structure and roughness on the surface of the molecular glass. The water repellency of the molecular glass could be controlled by tuning the uptake ratio of the n-alkane guest vapor.

Pillar[5]arenes with C₂F₅ substituents showed reversible amorphous–crystal transitions by uptake and release of n-alkane vapors. The amorphous–crystal transitions triggered macroscopic property change such as water repellency.

Rim-differentiated pillar[5]arene based nonporous adaptive crystals

The first rim-differentiated pillar[5]arene based nonporous adaptive crystals (NACs) were developed and used to separate dichloromethane from a halomethane mixture with 99.1% purity.

Chiral pillar[5]arene-functionalized silica microspheres: synthesis, characterization and enantiomer separation

Chiral pillar[5]arene-functionalized silica microspheres were prepared and characterized for the first time, which can be used as a new kind of chiral stationary phases for effective enantioseparation under reversed-phase and...

Separation of pyrrolidine from tetrahydrofuran by pillar[6]arene-based nonporous adaptive crystals

Pyrrolidine, an important feedstock in the chemical industry, is commonly produced via vapor-phase catalytic ammoniation of tetrahydrofuran (THF). Obtaining pyrrolidine with high purity and low energy cost has extremely high economic and environmental values. Here we offer a rapid and energy-saving method for adsorptive separation of pyrrolidine and THF by using nonporous adaptive crystals of per-ethyl pillar[6]arene (EtP6). EtP6 crystals show a superior preference towards pyrrolidine in 50 : 50 (v/v) pyrrolidine/THF mixture vapor, resulting in rapid separation. The purity of pyrrolidine reaches 95% in 15 min of separation, and after 2 h, the purity is found to be 99.9%. Single-crystal structures demonstrate that the selectivity is based on the stability difference of host–guest structures after uptake of THF or pyrrolidine and non-covalent interactions in the crystals. Besides, EtP6 crystals can be recycled efficiently after the separation process owing to reversible transformations between the guest-free and guest-loaded EtP6.

Here we offer a rapid and energy-saving method for adsorptive separation of pyrrolidine and tetrahydrofuran by using nonporous adaptive crystals of per-ethyl pillar[6]arene.

Symmetrically Tetra-functionalized Pillar[6]arenes Prepared by Fragment Coupling

Due to the highly symmetrical structures generated from one-pot syntheses, the partial functionalization of macrocycles is usually beset with low yields and onerous purifications of the target multifunctional macrocycles. To improve this circumstance, taking pillar[6]arenes as an example, a two-step fragment coupling method is developed for synthesizing symmetrically tetra-functionalized pillar[6]arenes, namely X-pillar[6]arenes. This method is simple and versatile, which makes hetero-fragment coupling and pre-functionalization available. Nine new macrocycles and a pillar[6]arene-based cage are prepared. In addition, one of the newly synthesized macrocycles, COOEtEtXP[6] , exhibits a strong cyan luminescence in the solid state under irradiation by 365 nm UV light. This emission originates from intramolecular through-space conjugation. Meanwhile, formation of a supramolecular polymer by multiple non-covalent intra/intermolecular interactions help rigidify the structure and make COOEtEtXP[6] an efficient solid-state emitter. It is believed that this fragment coupling can also be used to realize the multi-functionalization of other macrocycles.

Breathing Room: Restoring Free Rotation in a Schiff-Base Macrocycle through Endoperoxide Formation

Macrocyclization is a popular method for preparing hosts, but it can have unintended effects, like limiting molecular free rotation to yield mixtures of inseparable isomers. We report a [3 + 3] Schiff-base macrocycle (1) with anthracene bridges. Restricted rotation about the phenyl-anthracene bonds leads 1 to exist as a mixture of conformations (1^C_s and 1^C_3v). Macrocycle 1 was photooxidized to tris(endoperoxide) adduct 4, alleviating restricted rotation. These results were supported by spectroscopic, structural, and computational analyses.

Bio-inspired AIE pillar[5]arene probe with multiple binding sites to discriminate alkanediamines

Two functionalized pillar[5]arenes (H1 and H2) with significant AIE properties were synthesized. H2 is an excellent probe to selectively detect specific alkanediamines owing to its multiple binding sites, which result in the enhancement of emission based on the AIE mechanism and the induced-fit mechanism, and provides a new strategy to develop probes with high selectivity and sensitivity.

Multi-fold Sonogashira coupling: a new and convenient approach to obtain tetraalkynyl anthracenes with tunable photophysical properties

For the first time, a direct single-step one-pot route to access nine new symmetric tetraalkynylated anthracenes via Pd(CH₃CN)₂Cl₂/cataCXium®A catalyzed tetra-fold Sonogashira coupling is reported. Five of these tetraalkynylated anthracenes have been crystallographically characterized, with two of them exhibiting multiple interactions that significantly shorten the inter-planar distances in the solid-state structure. The rich photophysical properties exhibited by these molecules hold immense promise for future applications in sensors and optoelectronic devices. Two of the considered tetraalkynylated anthracenes comprising a D-π-A-π-D motif demonstrate solvatochromism and halochromism, with one of them showing a low bandgap of 1.79 eV. The remaining compounds demonstrate bandgaps in the range of 1.79-2.04 eV.

Film Nanoarchitectonics of Pillar[5]arene for High-Performance Fluorescent Sensing: a Proof-of-Concept Study

Substrates play crucial roles for the sensing performances of fluorescent films owing to their effect on the formation of a fluorescent adlayer. However, no such film has been developed through synthesizing a substrate with a defined structure. We herein report a kind of self-standing, uniform, and thickness tunable pillar[5]arene-based nanofilms to serve as substrates for fabricating fluorescent sensing films. In comparison with a glass plate, the pillar[5]arene-based nanofilms can ensure spatial and electronic isolation of immobilized fluorophores and circumvent aggregation-caused quenching in a film state. For conceptual proof, a formic acid fluorescent sensing film was developed through simple loading of a fluorophore, a 4-azetidine-1,8-naphthalimide derivative of cholesterol (NA-Ch), onto the prepared nanofilm. Sensing performance studies demonstrated that the fluorescent film showed a sensitive, fast, and highly selective response to formic acid in air with a detection limit of lower than 2.8 mg m^-3 and a response time of less than 3 s. Moreover, the sensing is fully reversible and highly repeatable. Further studies showed that the film sensor can be used for fast determination of methanol acidity via vapor sampling. Clearly, innovation of substrates with defined structures can be taken as an effective and efficient way to develop new sensing films via combination with known fluorophores.

Time-encoded bio-fluorochromic supramolecular co-assembly for rewritable security printing

Innovative fluorescence security technologies for paper-based information are still highly pursued nowadays because data leakage and indelibility have become serious economic and social problems. Herein, we report a novel transient bio-fluorochromic supramolecular co-assembly mediated by a hydrolytic enzyme (ALP: alkaline phosphatase) towards rewritable security printing. A co-assembly based on the designed tetrabranched cationic diethynylanthracene monomer tends to be formed by adding adenosine triphosphate (ATP) as the biofuel. The resulting co-assembly possesses a time-encoded bio-fluorochromic feature, upon successively hydrolyzing ATP with ALP and re-adding new batches of ATP. On this basis, the dynamic fluorescent properties of this time-encoded co-assembly system have been successfully enabled in rewritable security patterns via an inkjet printing technique, providing fascinating potential for fluorescence security materials with a biomimetic mode.

Pyridine-Conjugated Pillar[5]arene: From Molecular Crystals of Blue Luminescence to Red-Emissive Coordination Nanocrystals

A luminescent molecular crystal (P5bipy) and a Cu(I)-coordinated luminescent nanocrystal (Cu(I)-P5bipy) have been prepared concurrently using one conjugated pillar[5]arene macrocycle via a facile supramolecular self-assembling strategy. The molecular crystal shows enhanced luminescence compared with unmodified pillar[5]arene, attributed to its conjugated structure and staggered packing mode, while the coordination nanocrystal exhibits well-defined crystalline structures and long-lifetime triplet state emission along with pronounced solvochromic features.

Pyridine Detection Using Supramolecular Organic Frameworks Incorporating Cucurbit[10]uril

A physical impregnation method is presented in this study, providing a facile approach to encapsulating functional guest molecules (GMs) into robust crystalline supramolecular organic frameworks incorporating cucurbit[10]uril (Q[10]-SOF). As Q[10]-SOF has high evaporated pyridine affinity under normal atmospheric pressure, pyridine molecules in this method were successfully encapsulated into the nanospace formed by GMs and Q[10]-SOF while retaining their crystal framework, morphology, and high stability. GMs@Q[10]-SOF solid materials were found to respond to pyridine, being suitable to be used as solid sensors. Notably, Q[10]-SOF loading with pyrene exhibited a unique response to pyridine along with dramatic fluorescence quenching; loading with dansyl chloride exhibited a unique response to pyridine along with significant fluorescence enhancement, having a quick response within 60 s. Our findings represent a critical advancement in the design of pyridine detection and adsorption for commercial gas identification and sensing.

Synthesis of functionalized copillar[4+1]arenes and rotaxane as heteromultivalent scaffolds

In this study, novel copillar[4+1]arenes were used as central heteromultivalent scaffolds via orthogonal couplings with a series of biologically relevant molecules such as carbohydrates, α-amino acids, biotin and phenylboronic acid. Further modifications by introducing maleimides or cyclooctyne groups provided molecular probes adapted to copper-free click chemistry. An octa-azidated fluorescent rotaxane bearing two distinct ligands was also generated in a fully controlled manner.

Advances in applied supramolecular technologies

Supramolecular chemistry has successfully built a foundation of fundamental understanding. However, with this now achieved, we show how this area of chemistry is moving out of the laboratory towards successful commercialisation.

Solvent-dependent alignments and halogen-related interactions in inclusion crystals of adamantane-based macrocycle with pyridazine moieties

Six inclusion crystals were formed from crystallization of an adamantane-based macrocycle bearing pyridazine parts in various solvents. In inclusion crystals with cyclic ethers, halogen⋯halogen interactions between the macrocycles were observed.

Analysis of Solid-State Luminescence Emission Amplification at Substituted Anthracenes by Host-Guest Complex Formation

Small robust organic molecules showing solid-state luminescence are promising candidates for optoelectronic materials. Herein, we investigate a series of diphenylphosphanyl anthracenes [9-PPh2 -10-R-(C14 H8 )] and their sulfur oxidised analogues. The oxidation causes drastic changes in the molecular structure as the new orientation of the bulky (S)PPh2 substituent induces a strong butterfly bent structure of the anthracene core, which triggers a strong bathochromic shift resulting in a green solid-state fluorescence. As the emission properties change only slightly upon aggregation the origin of the emission is attributed to a typical monomer fluorescence. The host-guest complexes of [9-(S)PPh2 -10-Ethyl-(C14 H8 )] with four basic arenes reveal an emission enhancement up to five-times higher quantum yields compared to the pure host. Less interchromophoric interactions and a restriction of intramolecular motion within the host molecules due to fixation by weak C-H⋅⋅⋅π interactions with the co-crystallised arene are responsible for that emission enhancement.

Nanocomposite Based on Organic Framework-Loading Transition-Metal Co Ion and Cationic Pillar[6]arene and Its Application for Electrochemical Sensing of l-Ascorbic Acid

In this study, we constructed a highly sensitive and selective electrochemical sensing strategy for l-ascorbic acid (AA) based on a covalent organic framework (COF)-loading non-noble transition metal Co ion and macrocyclic cationic pillar[6]arene (CP6) nanocomposite (CP6-COF-Co). The COF plays a crucial role in anchoring the Co ion according to its crystalline porous and multiple coordination sites and has an outstanding performance for building an electrochemical sensing platform based on a unique two-dimensional structure. Accordingly, the transition-metal Co ion can be successfully anchored on the framework of COF and shows strong catalytic activity for the determination of AA. Moreover, introduction of host-guest recognition based on CP6 and AA can bring new properties for enhancing selectivity, sensitivity, and practical application in real environment. Host-guest interactions between CP6 and AA were evaluated by the ¹H NMR spectrum. When compared with other literatures, our method displayed a lower determination limit and broader linear range. To the best of our knowledge, this is the first study carried out for the non-noble transition-metal Co ion, COF, and pillar[6]arene hybrid material in sensing field, which has a potential value in sensing, catalysis, and preparation of advanced multifunction materials.

Vapochromism of Organic Crystals Based on Macrocyclic Compounds and Inclusion Complexes

Vapochromic materials, which change color and luminescence when exposed to specific vapors and gases, have attracted considerable attention in recent years owing to their potential applications in a wide range of fields such as chemical sensors and environmental monitors. Although the mechanism of vapochromism is still unclear, several studies have elucidated it from the viewpoint of crystal engineering. In this mini-review, we investigate recent advances in the vapochromism of organic crystals. Among them, macrocyclic molecules and inclusion complexes, which have apparent host–guest interactions with analyte molecules (specific vapors and gases), are described. When the host compound is properly designed, its cavity size and symmetry change in response to guest molecules, influencing the optical properties by changing the molecular inclusion and recognition abilities. This information highlights the importance of structure–property relationships resulting from the molecular recognition at the solid–vapor interface.