Hierarchical Two-Level Supramolecular Chirality of an Achiral Anthracene-Based Tetracationic Nanotube in Water

A Binaphthyl Macrocycle Exhibiting Circularly Polarized Luminescence: On-off Switch Triggered by Molecular Recognition

A series of D4-symmetric (S)-1,1'-binaphthyl cyclic tetramers were synthesized. The signs and intensities of circularly polarized luminescence (CPL) of the tetramers depend on the substituents, which were caused by differences of the binaphthyl dihedral angles in the excited state. The chiral dye with hydroxy groups did not exhibit CPL. However, this dye exhibited turned-on CPL upon addition of amino acids such as l-phenylalanine in an enantioselective and positive allosteric manner, and the glum value reached +7.3 × 10-3. The CPL was repeatedly switched on and off by changing temperature. The turn-on CPL was caused by the guest molecules expanding the binaphthyl dihedral angles with multiple hydrogen bonds. (+)-Andersen sulfinate also induced enantioselective turn-on CPL.

Contrasting Mechanochromic Luminescence of Enantiopure and Racemic Pyrenylprolinamides: Elucidating Solid-State Excimer Orientation by Circularly Polarized Luminescence

Circularly polarized luminescence (CPL) and mechanochromic luminescence (MCL) have independently made substantial progress in recent years. However, the exploration of MCL in solid-state CPL materials, which holds practical significance, is still in its infancy. Herein, we report the MCL properties of readily accessible chiral pyrenylprolinamides bearing tert-butoxycarbonyl (Boc) or 2,2,2-trichloroethoxycarbonyl (Troc) groups. Enantiopure crystals of the Boc derivative display a greater MCL wavelength shift than racemic crystals, while the Troc derivative exhibit the opposite trend. Most notably, the enantiopure crystals show mechanochromic CPL. Unlike in previous examples, where CPL is quenched upon amorphization, robust CPL spectra were observed even in the amorphous states. By applying the excimer chirality rule, we have, for the first time, acquired insights into the excited-state structures within mechanically generated amorphous states. These findings offer a novel design strategy for developing mechanochromic CPL materials, paving the way for the future advancements in this emerging field.

Advances in Chiral Macrocycles: Molecular Design and Applications

Chiral macrocycles have recently emerged as promising materials for enantioselective recognition, asymmetric catalysis, and circularly polarized luminescence (CPL) due to their terminal-free structure, preorganized chiral cavities, and unique host-guest and self-assembly properties. This review summarizes recent advances in the design and synthesis of chiral macrocycles with central, axial, helical, and planar chirality, each imparting distinct structural and chiroptical characteristics. We highlight key strategies for constructing these macrocycles and their applications in optoelectronic and catalytic systems. Emphasis is placed on the balance between rigidity and flexibility in macrocycle design, essential for effective molecular recognition, adaptable catalysis, and CPL. We conclude with perspectives on future opportunities, anticipating ongoing developments in chiral macrocycle research.

Biofuel-Driven Stepping Chiral Supramolecular Transfer Container

Herein, we reported a biofuel-driven recyclable chiral supramolecular transfer container based on hexacationic triphenylamine cage and nucleotides. Possessing rotatable paddle rigid backbones, the artificial receptor effectively encapsulated nucleotides with a high binding constant up to 5.37×105 M-1 in water, displaying guest-induced efficient fluorescence enhancement with quantum yield increased from 6.5 % to 16.6 %. Especially, the achiral cage could effectively bind with adenosine triphosphate to activate chirality transfer from substrates to the single molecular container, giving circularly polarized luminescence at 575 nm and positive Cotton effect peaks with significant asymmetric factor (gabs=+6.4×10-4). Meanwhile, the adaptive chiral supramolecule not only has reversible thermal responsiveness but also could stepwise regulate chirality transfer by the catalysis of hexokinase and apyrase in tandem, showing recovery adaptive chirality after refueled, achieving dynamically regulated programmable multistate chiral luminescent supramolecules. Therefore, the biofuel-driven chiral supramolecular transfer container could be successfully applied in chiral logic gates and multilevel information encryption, providing new insight into intelligent chiral materials.

Chirality Interplay between the Interior and Exterior of Metal-Organic Cages

A series of metal-organic cages featuring two stereogenic elements, in terms of the twisting of amide moieties within the ligand backbones and the rotation of diazaanthracene segments along the ligand ridges, were exploited. These two chiral components are correlative and serve as relays for transmitting chirality information between the internal and external cages. The chirality information induced by a chiral guest inside the cage cavity can pass through the cage framework and influence the orientation of the diazaanthracene segments on the periphery of the cage. In turn, the chirality of a stereogenic center within the diazaanthracene segments can transfer back into the cavity, enabling discrimination of enantiomeric guests.

Unraveling the structure-chirality sensing relationship between achiral anthracene-based tetracationic nanotubes and nucleosides in aqueous host-guest complexation

In biological systems, nucleosides play crucial roles in various physiological processes. In this study, we designed and synthesized four achiral anthracene-based tetracationic nanotubes (1-4) as artificial hosts and chiroptical sensors for nucleosides in aqueous media. Notably, different nanotubes exhibit varied chirality sensing on circular dichroism (CD)/circularly polarized luminescence (CPL) spectra through the host-guest complexation, which prompted us to explore the factors influencing their chiroptical responses. Through systematic host-guest experiments, the structure-chirality sensing relationship between achiral anthracene-based tetracationic nanotubes and nucleosides in the host-guest complexation was unraveled. Firstly, the CD response originates from the anthracene rings situated at the side-wall position, resulting from the right-handed (P)- or left-handed (M)-twisted conformation of the macrocyclic structure. Secondly, the CPL signal is influenced by the presence of anthracene rings at the linking-wall position, which results from intermolecular chiral twisted stacking between these anthracene rings. Therefore, these nanotubes can serve as chiroptical sensor arrays to enhance the accuracy of nucleotide recognition through principal component analysis (PCA) analysis based on the diversified CD spectra. This study provides insights for the construction of adaptive chirality from achiral nanotubes with dynamic conformational nature and might facilitate further design of chiral functional materials for several applications.

Handedness-Inverted and Stimuli-Responsive Circularly Polarized Luminescent Nano/Micromaterials Through Pathway-Dependent Chiral Supramolecular Polymorphism

The precise manipulation of supramolecular polymorphs has been widely applied to control the morphologies and functions of self-assemblies, but is rarely utilized for the fabrication of circularly polarized luminescence (CPL) materials with tailored properties. Here, this work reports that an amphiphilic naphthalene-histidine compound (NIHis) readily self-assembled into distinct chiral nanostructures through pathway-dependent supramolecular polymorphism, which shows opposite and multistimuli responsive CPL signals. Specifically, NIHis display assembly-induced CPL from the polymorphic keto tautomer, which become predominant during enol-keto tautomerization shifting controlled by a bulk solvent effect. Interestingly, chiral polymorphs of nanofiber and microbelt with inverted CPL signals can be prepared from the same NIHis monomer in exactly the same solvent compositions and concentrations by only changing the temperature. The tunable CPL performance of the solid microbelts is realized under multi external physical or chemical stimuli including grinding, acid fuming, and heating. In particular, an emission color and CPL on-off switch based on the microbelt polymorph by reversible heating-cooling protocol is developed. This work brings a new approach for developing smart CPL materials via supramolecular polymorphism engineering.

Selective recognition and enrichment of C70 over C60 using an anthracene-based nanotube

Selective recognition and enrichment of fullerenes (e.g., C60 and C70) remains challenging due to the same diameter and geometrical similarity. Herein, we report a hexagonal anthracene-based nanotube (1) through a one-pot Suzuki-Miyaura cross-coupling reaction. With anthracene-based side walls and pyridine linkers, 1 features a nano-scale tubular cavity measuring 1.2 nm in diameter and 0.9 nm in depth, along with pH-responsive properties. Interestingly, the electron-rich 1 shows high binding affinity (K a ≈ 106 M-1) and selectivity (K s ≈ 140) to C70 over C60 in toluene, resulting from their different contribution of π-π interactions with the host. The protonation of 1 simultaneously alters the electronic properties within the nanotube, resulting in the release of the fullerene guests. Lastly, the selective recognition and pH stimuli-responsive properties of the nanotube have been utilized to enrich C70 from its low-content mixtures of fullerenes in chloroform.

Biomimetic Hydrogen-Bonded G ⋅ C ⋅ G ⋅ C Quadruplex within a Tetraphenylethene-Based Octacationic Spirobicycle in Water

In biological systems, nucleotide quadruplexes (such as G-quadruplexes) in DNA and RNA that are held together by multiple hydrogen bonds play a crucial functional role. The biomimetic formation of these hydrogen-bonded quadruplexes captured by artificial systems in water poses a significant challenge but can offer valuable insights into these complex functional structures. Herein, we report the formation of biomimetic hydrogen-bonded G ⋅ C ⋅ G ⋅ C quadruplex captured by a tetraphenylethene (TPE) based octacationic spirobicycle (1). The spirobicyclic compound possesses a three-dimensional (3D) crossing dual-cavity structure, which enables the encapsulation of four d(GpC) dinucleotide molecules, thereby realizing 1 : 4 host-guest complexation in water. The X-ray structure reveals that four d(GpC) molecules further form a two-layer G ⋅ C ⋅ G ⋅ C quadruplex with Watson-Crick hydrogen bonds, which are stabilized within the dual hydrophobic cavities of 1 through the cooperative non-covalent interactions of hydrogen bonds, CH⋅⋅⋅π interactions, and hydrophobic effect. Due to the dynamically-rotational propeller chirality of TPE units, 1 with adaptive chirality can further serve as a chiroptical sensor to exhibit opposite Cotton effects with mirror-image CD spectra for the pH-dependent hydrogen-bonded assemblies of d(GpC) including the Watson-Crick G ⋅ C ⋅ G ⋅ C (pH 9.22) and Hoogsteen G ⋅ C+ ⋅ G ⋅ C+ (pH 5.74) quartets through the host-guest chirality transfer in water.

"Gear-driven"-type chirality transfer of tetraphenylethene-based supramolecular organic frameworks for peptides in water

Chirality transfer for natural chiral biomolecules can reveal the indispensable role of chiral structures in life and can be used to develop the chirality-sensing biomolecular recognition. Here, we report the synthesis and characterization of a series of achiral supramolecular organic frameworks (SOF-1, SOF-2, and SOF-3), constructed from cucurbit[8]uril (CB[8]) and tetraphenylethene (TPE) derivatives (1, 2, and 3), respectively, as chirality-sensing platforms to explore their chirality transfer mechanism for peptides in water. Given the right-handed (P) and left-handed (M) rotational conformation of TPE units and the selective binding of CB[8] to aromatic amino acids, these achiral SOFs can be selectively triggered in water by peptides containing N-terminal tryptophan (W) and phenylalanine (F) residues into their P- or M-rotational conformation, exhibiting significantly different circular dichroism (CD) spectra. Although various peptides have the same l-type chiral configuration, they can induce positive CD signals of SOF-1 and negative CD signals of SOF-2 and SOF-3, respectively. Based on the structural analysis of the linkage units between CB[8] and TPE units in these SOFs, a "gear-driven"-type chirality transfer mechanism has been proposed to visually illustrate the multiple-step chirality transfer process from the recognition site in the CB[8]'s cavity to TPE units. Furthermore, by utilizing the characteristic CD signals generated through the "gear-driven"-type chirality transfer, these SOFs can serve as chiroptical sensor arrays to effectively recognize and distinguish various peptides based on their distinctive CD spectra.

A general supramolecular strategy for fabricating full-color-tunable thermally activated delayed fluorescence materials

Developing a facile and feasible strategy to fabricate thermally activated delayed fluorescence materials exhibiting full-color tunability remains an appealing yet challenging task. In this work, a general supramolecular strategy for fabricating thermally activated delayed fluorescence materials is proposed. Consequently, a series of host-guest cocrystals are prepared by electron-donating calix[3]acridan and various electron-withdrawing guests. Owing to the through-space charge transfer mediated by multiple noncovalent interactions, these cocrystals all display efficient thermally activated delayed fluorescence. Especially, by delicately modulating the electron-withdrawing ability of the guest molecules, the emission colors of these cocrystals can be continuously tuned from blue (440 nm) to red (610 nm). Meanwhile, high photoluminescence quantum yields of up to 87% is achieved. This research not only provides an alternative and general strategy for the fabrication of thermally activated delayed fluorescence materials, but also establishes a reliable supramolecular protocol toward the design of advanced luminescent materials.

Machine-Learning-Driven G-Quartet-Based Circularly Polarized Luminescence Materials

Circularly polarized luminescence (CPL) materials have garnered significant interest due to their potential applications in chiral functional devices. Synthesizing CPL materials with a high dissymmetry factor (glum ) remains a significant challenge. Inspired by efficient machine learning (ML) applications in scientific research, this work demonstrates ML-based techniques for the first time to guide the synthesis of G-quartet-based CPL gels with high glum values and multiple chiral regulation strategies. Employing an "experiment-prediction-verification" approach, this work devises a ML classification and regression model for the solvothermal synthesis of G-quartet gels in deep eutectic solvents. This process illustrates the relationship between various synthesis parameters and the glum value. The decision tree algorithm demonstrates superior performance across six ML models, with model accuracy and determination coefficients amounting to 0.97 and 0.96, respectively. The screened CPL gels exhibiting a glum value up to 0.15 are obtained through combined ML guidance and experimental verification, among the highest ones reported till now for biomolecule-based CPL systems. These findings indicate that ML can streamline the rational design of chiral nanomaterials, thereby expediting their further development.

Chiral TPE Foldamers in Macrocycles: Aggregation Enhanced Emission and Circularly Polarized Luminescence

Chiral macrocycles with circularly polarized luminescence (CPL) have attracted increasing attention due to the rigid structure, symmetrical chiral geometry and large luminescence dissymmetry factors (glum ). However, most chiral macrocycles are more emissive in solutions but have weakened fluorescence quantum yields (ΦF ) in aggregates, limiting their further application. In this paper, chiral macrocycle R/S-PhTPE was synthesized by combining chiral macrocycle architectonics with Z-o-phenyltetraphenylethylene (PhTPE) foldamer. Enhanced solution state emission and characteristic aggregation enhanced emission (AEE) effect can be observed for R/S-PhTPE due to the folded PhTPE conformation. Macrocycle immobilization and folded conformation endow PhTPE moiety with stable helical conformation. Most importantly, R/S-PhTPE exhibits opposite CPL signals compared with common chiral TPEs, demonstrating the evident impact of folded conformation. This work reports the first and deep insights into the chiroptical properties of chiral PhTPE foldamers, and will provide a new strategy to tune ΦF and CPL signals of AIE active chiral macrocycles.

Advances in circularly polarized luminescence materials based on chiral macrocycles

Development of circularly polarized luminescence (CPL) materials utilizing supramolecular strategies has recently attracted increasing interest in supramolecular chemistry and materials science. Chiral macrocycles, especially chiral macrocyclic hosts, have stable structures, adjustable internal cavities to encapsulate different guests, and host-guest complexation to induce special photophysical properties. Consequently, various CPL materials based on chiral macrocycles have been developed during the last decade. To gain a better understanding of this rapidly developing research area, it is necessary and also important to summarize the advances in CPL materials based on chiral macrocycles. In this review, CPL materials from different chiral macrocycles, especially classical and newly reported chiral macrocyclic hosts and their derivatives, will be comprehensively summarized. It is believed that this review will be of guiding significance and also very helpful for the development of macrocyclic chemistry and CPL materials.

A biocompatible pure organic porous nanocage for enhanced photodynamic therapy

Porphyrin-based photosensitizers have been widely utilized in photodynamic therapy (PDT), but they suffer from deteriorating fluorescence and reactive oxygen species (ROS) due to their close π-π stacking. Herein, a biocompatible pure organic porphyrin nanocage (Py-Cage) with enhanced both type I and type II ROS generation is reported for PDT. The porphyrin skeleton within the Py-Cage is spatially separated by four biphenyls to avoid the close π-π stacking within the nanocage. The Py-Cage showed a large cavity and high porosity with a Brunauer-Emmett-Teller surface area of over 300 m2 g-1, facilitating a close contact between the Py-Cage and oxygen, as well as the fast release of ROS to the surrounding microenvironment. The Py-Cage shows superb ROS generation performance over its precursors and commercial ones such as Chlorin E6 and Rose Bengal. Intriguingly, the cationic π-conjugated Py-Cage also shows promising type I ROS (superoxide and hydroxyl radicals) generation that is more promising for hypoxic tumor treatment. Both in vitro cell and in vivo animal experiments further confirm the excellent antitumor activity of the Py-Cage. As compared to conventional metal coordination approaches to improve PDT efficacy of porphyrin derivatives, the pure organic porous Py-Cage demonstrates excellent biocompatibility, which is further verified in both mice and rats. This work of an organic porous nanocage shall provide a new paradigm for the design of novel, biocompatible and effective photosensitizers for PDT.

Chiroptical Amplification of Induced Circularly Polarized Luminescence in Nucleotide-Templated Supramolecular Polymer

Efficient circularly polarized luminescence (CPL) from purely organic molecules holds great promise for applications in displays, sensing, and bioimaging. However, achieving high dissymmetry values (glum ) from organic chromophores remains a significant challenge. Herein, we present a bioinspired approach using adenosine triphosphate (ATP)-triggered supramolecular polymerization of a naphthalene diimide-derived monomer (ANSG) to induce CPL with a remarkable glum value of 1.1×10-2 . The ANSG molecules undergo a templated, chiral self-assembly through a cooperative growth mechanism in the presence of ATP, resulting in scrolled nanotubes with aggregation-induced enhanced emission (AIEE) and induced CPL. Furthermore, we demonstrate the concept of chiroptical amplification of induced CPL by efficiently amplifying asymmetry using a mixture of chiral ATP and achiral pyrophosphate. This innovative approach opens numerous opportunities in the emerging field of circularly polarized luminescence.

Chiral Adaptive Induction of an Achiral Cucurbit[8]uril-Based Supramolecular Organic Framework by Dipeptides in Water

Chiral induction by natural biomolecules can reveal the indispensable role of chiral structures in life and can be used to develop the chirality-sensing biomolecular recognition. Here, we present the synthesis and characterization of an achiral supramolecular organic framework (SOF-1) constructed from cucurbit[8]uril (CB[8]) and hexaphenylbenzene (HPB) derivative (1) in water. Due to the propeller-like rotational chiral conformation of HPB units and the specific recognition properties of CB[8], SOF-1 demonstrates chiral adaptive induction in water when interacting with the N-terminal Trp-/Phe-containing dipeptides including L-TrpX and L-PheX (X is an amino acid residue), respectively, exhibiting contrasting circular dichroism (CD) and circularly polarized luminescence (CPL) spectra. Consequently, SOF-1 has been developed as a supramolecular host and chiroptical sensor capable of recognizing and distinguishing the sequence-opposite Trp-/Phe-containing dipeptide pairs including L-TrpX/L-XTrp and L-PheX/L-XPhe based on the sequence-selective CD responses.

Adaptive Planar Chirality of Pillar[5]arenes Invertible by n-Alkane Lengths

Chirality of host molecules can be induced and/or inverted by the guest molecules. However, the adapting chirality of hosts to the length of n-alkanes remains a great challenge because n-alkanes are neutral, achiral, and linear molecules, resulting in a weak interaction with most compounds. Herein, we report a system with chirality adapted to n-alkane lengths, using a pillar[5]arene-based macrocyclic host, S-Br, which contains five stereogenic carbons and five terminal bromine atoms on each rim. The electron-rich cavity of S-Br could include n-alkanes and the planar-chiral isomers sensitively inverted in response to the lengths of the complexed n-alkanes. The inclusion of a short n-alkane such as n-pentane made S-Br more inclined to be in the pS-form, whereas the inclusion of long n-alkanes such as n-heptane made the pR-form more favorable. The difference in the stability of the isomers was supported by the crystal structures and the theoretical calculations. Furthermore, temperature drives the adaptive chirality of S-Br with n-alkanes. An n-alkane with middle length, n-hexane, showed the dominance of the pR-form of S-Br at a higher temperature, whereas the pS-form was shown at a lower temperature.

Circularly polarized luminescence in molecular recognition systems: Recent achievements

Circularly polarized luminescence (CPL) dyes are recognized to be new generation materials and have been actively developed. Molecular recognition systems provide nice approaches to novel CPL materials, such as stimuli-responsive switches and chemical sensing materials. CPL may be induced simply by mixing chiral or achiral, luminescent or nonluminescent host and guest; there are several combinations. Molecular recognition can potentially save time and effort to construct well-ordered chiral structures with noncovalent attractive interactions as compared with the multi-step synthesis of covalently bonded dyes. It is a challenging subject to engage molecular recognition events with CPL, and it is important and interesting to see how it is achieved. In fact, simple molecular recognition systems can even enable the fine adjustment of CPL performance and detailed conformational/configurational analysis of the excited state. Here we overview the recent achievements of simple host-guest complexes capable of exhibiting CPL, summarizing concisely the host/guest structures, CPL intensities, and characteristics.

Chiral adaptive recognition with sequence specificity of aromatic dipeptides in aqueous solution by an achiral cage

Sequence-specific recognition of peptides and proteins by synthetic compounds or systems remains a huge challenge in biocompatible media. Here, we report the chiral adaptive recognition (CAR) with sequence specificity of aromatic dipeptides in a purely aqueous solution using an achiral tetraphenylethene-based octacationic cage (1) as both a molecular receptor and chiroptical sensor. 1 can selectively bind and dimerize aromatic dipeptides to form 1 : 2 host-guest complexes with high binding affinity (>10¹⁰ M^-2), especially up to ∼10¹⁴ M^-2 for TrpTrp. Given the dynamic rotational conformation of TPE units, achiral 1 can exhibit chiral adaptive responses with mirror-symmetrical circular dichroism (CD) and circularly polarized luminescence (CPL) spectra to enantiomeric dipeptides via supramolecular chirality transfer in the host-guest complexes. Furthermore, this CAR with sequence specificity of 1 can be applied for molecular recognition of TrpTrp- or PhePhe-containing tetrapeptides, polypeptides (e.g., amyloid β-peptide_1-20 and somatostatin), and proteins (e.g., human insulin) with characteristic CD responses.

Dual supramolecular chirogenesis based on platinum(II) metallotweezers

Optically active platinum(II) metallotweezers demonstrate both self-complexation and host-guest complexation capabilities, leading to two distinct supramolecular chirogenic signals in the visible region.

Cyclic arrays of five pyrenes on one rim of a planar chiral pillar[5]arene

Spatial arrangement of multiple planar chromophores is an emerging strategy for molecule-based chiroptical materials via easy and systematic synthesis. We attached five pyrene planes to a chiral macrocycle, pillar[5]arene, producing a set of chiroptical molecules in which pyrene-derived absorption and emission were endowed with dissymmetry by effective transfer of chiral information. The chiroptical response was dependent on linker structures and substituted patterns because of variable interactions between pyrene units. One of these hybrids showed larger dissymmetry factor and response wavelength (g lum = 7.0 × 10-3 at ca. 547 nm) than reported pillar[5]arene-based molecules using the pillar[5]arene cores as parts of photo-responsive π-conjugated units.

Dynamically stable and amplified circularly polarized excimer emission regulated by solvation of chiral co-assembly process

Chiral supramolecular assembly has been assigned to be one of the most favorable strategies for the development of excellent circularly polarized luminescent (CPL)-active materials. Herein, we report our study of an achiral boron-containing pyrene (Py)-based chromophore (PyBO) as a circularly polarized excimer emission (CPEE) dye induced by chiral co-assemblies containing chiral binaphthyl-based enantiomers (R/S-M). Chiral co-assembly R/S-M-(PyBO)4 fresh film spin-coated from toluene solution can exhibit orderly nanofibers and strong green CPEE (λem = 512 nm, gem = ±0.45, ΦFL = 51.2 %) resulting from an achiral PyBO excimer. In contrast, only a very weak blue CPL was observed (λem = 461 nm, gem = ±  0.0125, ΦFL = 19.0 %) after 187 h due to PyBO monomer emission as spherulite growth. Interestingly, this kind of chiral co-assembly R-M-(PyBO)4-T film from tetrahydrofuran (THF) solution retains uniform morphology and affords the most stable and strongest CPEE performance (λem = 512 nm, gem = + 0.62, ΦFL = 53.3 %) after 10 days.

Fluorescent cyclophanes and their applications

With the serendipitous discovery of crown ethers by Pedersen more than half a century ago and the subsequent introduction of host-guest chemistry and supramolecular chemistry by Cram and Lehn, respectively, followed by the design and synthesis of wholly synthetic cyclophanes-in particular, fluorescent cyclophanes, having rich structural characteristics and functions-have been the focus of considerable research activity during the past few decades. Cyclophanes with remarkable emissive properties have been investigated continuously over the years and employed in numerous applications across the field of science and technology. In this Review, we feature the recent developments in the chemistry of fluorescent cyclophanes, along with their design and synthesis. Their host-guest chemistry and applications related to their structure and properties are highlighted.

Circular Dichroism Based Chirality Sensing with Supramolecular Host-Guest Chemistry

Optical methods are promising to address the ever-increasing demands for chirality analysis in drug discovery and related fields because they are amenable to high-throughput screening. Circular dichroism-based chiroptical sensing using host-guest chemistry is especially appealing due to the fast equilibrium kinetics, wide substrate scope, and potential for sustainable development. In this Minireview, we give an overview on this emerging field. General aspects of molecular recognition and chirality transfer are analyzed. Chirality sensors are discussed by dividing them into three classes according to their structural features. Applications of these chirality sensors for chirality analysis of the products of asymmetric reactions and for the real-time monitoring of reaction kinetics are demonstrated with selected examples. Moreover, challenges and research directions in this field are also highlighted.

ATP-Induced Emergent Circularly Polarized Luminescence and Encryption

Biomimetic ATP-driven supramolecular assembly is important to understand various biological processes and dissipative systems. Here, we report an ATP-driven chiral assembly exhibiting circularly polarized luminescence (CPL) via the interaction of an achiral terpyridine-based Zn^II complex with nucleotides. It was found that while the metal complexes could co-assemble with the nucleotides to form fluorescent assemblies, only a combination of furan-substituted terpyridine complex and ATP showed an intense CPL with a dissymmetry factor (g_lum ) as high as 0.20. This means that the complex could recognize ATP using CPL as a readout signal, thus providing an example of ATP encryption. Interestingly, when ATP was transferred into ADP or AMP under enzymatic hydrolysis, the CPL decreases or disappears. Addition of ATP generates CPL again, thus producing an ATP-induced CPL system. This work presents the first example of ATP-induced CPL and encryption.

A Calix[3]acridan-Based Host-Guest Cocrystal Exhibiting Efficient Thermally Activated Delayed Fluorescence

A supramolecular strategy to construct thermally activated delayed fluorescence (TADF) materials through host-guest charge transfer interactions was proposed. Consequently, a new class of macrocycle namely calix[3]acridan was conveniently synthesized in 90 % yield. The host-guest cocrystal formed by calix[3]acridan and 1,2-dicyanobenzene exhibited efficient TADF properties due to intense intermolecular charge transfer interactions. Moreover, the spatially separated highest occupied molecular orbital and lowest unoccupied molecular orbital resulted in a very small singlet-triplet energy gap of 0.014 eV and hence guaranteed an efficient reverse intersystem crossing for TADF. Especially, a high photoluminescence quantum yield of 70 % was achieved, and it represents the highest value among the reported intermolecular donor-acceptor TADF materials.

Chiral proline-substituted porous organic cages in asymmetric organocatalysis

The efficient preparation of chiral porous organic cages (POCs) with specific functions is challenging, and their application in asymmetric catalysis has not previously been explored. In this work, we have achieved the construction of chiral POCs based on a supramolecular tetraformyl-resorcin[4]arene scaffold with different chiral proline-modified diamine ligands and utilizing dynamic imine chemistry. The incorporation of V-shaped or linear chiral diamines affords the [4 + 8] square prism and [6 + 12] octahedral POCs respectively. The appended chiral proline moieties in such POCs make them highly active supramolecular nanoreactors for asymmetric aldol reactions, delivering up to 92% ee. The spatial distribution of chiral catalytic sites in these two types of POCs greatly affects their catalytic activities and enantioselectivities. This work not only lays a foundation for the asymmetric catalytic application of chiral POCs, but also contributes to our understanding of the catalytic function of biomimetic supramolecular systems.

Tunable Excimer Circularly Polarized Luminescence in Isohexide Derivatives from Renewable Resources

Organic compounds showing circularly polarized luminescence (CPL) are at the forefront of novel applications and technologies. Here we show the synthesis and chiroptical properties of pyrene and perylene derivatives of inexpensive chiral scaffolds: isomannide and isosorbide. Low‐intensity ECD spectra were obtained, suggesting the absence of chromophore interaction in the ground state, except in the case of isomannide bis‐perylenecarboxylate, whose ECD spectrum showed a positive exciton couplet. All isomannide derivatives, with the only exception of the one containing a pyrenecarboxylate and a perylenecarboxylate, exhibited excimer CPL spectra, whereas isosorbide derivatives did not show any CPL. Isomannide derivatives bearing two pyrenecarboxylate or two pyrenylacetate groups showed positive CPL emission with dissymmetry factors up to 10⁻², which depends on the conformational freedom of the appended units. The CPL sign, Stokes shift and order of magnitude of dissymmetry factor were reproduced by excited‐state calculations on a representative compound. Interestingly, the mixed derivative containing pyrenic units with different spacing from the isomannide scaffold showed an oppositely signed excimer band with respect to the homo‐substituted derivatives.

Circularly polarized luminescent porous crystalline nanomaterials

Circularly polarized luminescence (CPL)-active materials have attracted exclusive attention because of their wide potential applications in low-power-consumption displays, encrypted information storage, chiroptical sensors, and so on. However, there is always a trade-off between the luminescence dissymmetry factor (g_lum) and luminescence quantum yield, which are two critical parameters. Therefore, developing materials with both large g_lum values and high luminescence efficiency is a key issue for constructing high-efficiency CPL materials. To date, chiral porous crystalline nanomaterials (PCNMs) including metal-organic frameworks (MOFs), porous organic-cages (POCs), metal-organic cages (MOCs), and supramolecular organic frameworks (SOFs), have shown excellent potential for solving this problem and achieving functional CPL-active materials. In this review, we will summarize several approaches for fabricating CPL-active PCNMs, such as direct synthesis, chirality induction, and symmetry breaking. Furthermore, with flexibly tunable structures and comprehensive host-guest chemistry, modulation and amplification of CPL can be achieved in these PCNMs. We would like to provide insight and perspective that PCNMs can act as an efficient platform in the CPL research field.

Phthalocyanine-Triggered Helical Dipeptide Nanotubes with Intense Circularly Polarized Luminescence

Nanotubes with circularly polarized luminescence (CPL) are attracting much attention due to many potential applications, such as chiroptical materials, displays, and sensing. However, it remains a challenge to change the assemblies of ordinarily molecular building blocks into CPL supramolecular nanotubes. Herein, the regulation of quite common dipeptide (Fmoc-FF) assemblies into unprecedented helical nanotubes exhibiting intense CPL is reported by simply doping a few phthalocyanine (octakis(carboxyl)phthalocyaninato zinc complex (Pc)) molecules. Interestingly, altering the Fmoc-FF/Pc molar ratios over a wide range cannot change the nanotubes structures according to transmission electron microscopy (TEM) and atomic force microscope (AFM) measurements. Although molecular dynamics simulations suggest that the noncovalent interactions between Fmoc-FF and Pc are quite weak, few Pc molecules can still change the secondary structures of a large number of Fmoc-FF assemblies, which hierarchically form helical supramolecular nanotubes with long-range ordered molecular packing, leading to intense CPL signals with large luminescence dissymmetry factor (g_lum  = 0.04). Consequently, the chiral reorganization of Fmoc-FF assemblies is dependent on the coassembly between Pc molecule and Fmoc-FF supramolecular architectures. These results open the possibility for the fine-tuning of helix and supramolecular nanotubes with CPL properties by using a small number of cofactors.

Synthesis and aqueous anion recognition of an imidazolium-based nonacationic cup

An imidazolium-based nonacationic cup (1·9X; X = PF₆^- or Cl^-) was synthesized via step-by-step S_N2 reactions without using any template. The water-soluble 1·9Cl^- as a molecular container can encapsulate anionic nucleoside triphosphate and dinucleotide molecules (e.g., ATP and NADH) inside its cavity through hydrogen bonds and electrostatic interactions in aqueous solution.

Chiral exciplex dyes showing circularly polarized luminescence: extension of the excimer chirality rule

A series of axially chiral binaphthyls and quaternaphthyls possessing two kinds of aromatic fluorophores, such as pyrenyl, perylenyl, and 4-(dimethylamino)phenyl groups, arranged alternately were synthesized by a divergent method. In the excited state, the fluorophores selectively formed a unidirectionally twisted exciplex (excited heterodimer) by a cumulative steric effect and exhibited circularly polarized luminescence (CPL). They are the first examples of a monomolecular exciplex CPL dye. This versatile method for producing exciplex CPL dyes also improved fluorescence intensity, and the CPL properties were not very sensitive to the solvent or to the temperature owing to the conformationally rigid exciplex. This systematic study allowed us to confirm that the excimer chirality rule can be applied to the exciplex dyes: left- and right-handed exciplexes with a twist angle of less than 90° exhibit (-)- and (+)-CPL, respectively.