Lemniscular [16]Cycloparaphenylene: A Radially Conjugated Figure-Eight Aromatic Molecule

Synthesis of All-Benzene Multi-Macrocyclic Nanocarbons by Post-Functionalization of meta-Cycloparaphenylenes

Expanding the diversity of multi-macrocyclic nanocarbons, particularly those with all-benzene scaffolds, represents intriguing yet challenging synthetic tasks. Complementary to the existing synthetic approaches, here we report an efficient and modular post-functionalization strategy that employs iridium-catalyzed C-H borylation of the highly strained meta-cycloparaphenylenes (mCPPs) and an mCPP-derived catenane. Based on the functionalized macrocyclic synthons, a number of novel all-benzene topological structures including linear and cyclic chains, polycatenane, and pretzelane have been successfully prepared and characterized, thereby showcasing the synthetic utility and potential of the post-functionalization strategy.

Synthesis and Properties of a Strained Triple Nanohoop

A strained triple nanohoop with a shared central benzene unit is synthesized using a threefold intramolecular ring-closing approach. Among the five possible constitutional isomers, the isomer with the highest D3h symmetry is isolated, the structure of which contains three nanohoop blades and a central hexaphenylbenzene unit. The structure is elucidated using NMR spectroscopy and mass spectrometry. The optical and electrochemical properties are investigated, revealing a moderate fluorescence quantum yield of 40 %. A water-soluble nanomaterial is prepared using a nanoparticle encapsulation method, and a fluorescence quantum yield of 10 % is retained, which demonstrates the potential of the nanomaterial in biological systems.

Cyclic Azahelicene Dimers Showing Bright Circularly Polarized Luminescence and Selective Fluoride Recognition

Although helicenes are promising molecules, the synthetic difficulty and tediousness have often been problems, and only small amounts of optically pure helicenes have been obtained by using chiral HPLC in most cases. Herein, aza[7]helicenes or closed-aza[7]helicenes with (1R)-menthyl substituents were selectively synthesized via the intramolecular Scholl reaction, and the diastereomeric pairs were separated by silica gel column chromatography. The optically pure helicenes were further transformed into the corresponding cyclic dimers, and the chiroptical properties were investigated. The rigid π-frameworks of the dimers led to the high molar extinction coefficients and fluorescence quantum yields, while the twisted helicene moieties induced clear Cotton effects and CPL in the visible region, and the high CPL brightness (BCPL) was achieved. Furthermore, the cyclic dimers were found to have the macrocyclic cavity with the two NH groups suitable for the selective binding of a fluoride anion, which induced significantly redshifted fluorescence and CPL in the red region.

Synthesis of a novel twisted π-conjugated macrocycle via double Friedel-Crafts reaction and its physical properties

We synthesized a cyclic molecule from diarylalkynes and Meldrum's acid derivatives as the methylenation reagent via double Friedel-Crafts reaction. Single-crystal X-ray structure analysis confirmed the twisted structure of the molecule. We also investigated their physical properties and homoconjugation by UV-Vis, photoluminescence, DFT and TD-DFT calculations.

Polycationic Open-Shell Cyclophanes: Synthesis of Electron-Rich Chiral Macrocycles, and Redox-Dependent Electronic States

π-Conjugated chiral nanorings with intriguing electronic structures and chiroptical properties have attracted considerable interests in synthetic chemistry and materials science. We present the design principles to access new chiral macrocycles (1 and 2) that are essentially built on the key components of main-group electron-donating carbazolyl moieties or the π-expanded aza[7]helicenes. Both macrocycles show the unique molecular conformations with a (quasi) figure-of-eight topology as a result of the conjugation patterns of 2,2',7,7'-spirobifluorenyl in 1 and triarylamine-coupled aza[7]helicene-based building blocks in 2. This electronic nature of redox-active, carbazole-rich backbones enabled these macrocycles to be readily oxidized chemically and electrochemically, leading to the sequential production of a series of positively charged polycationic open-shell cyclophanes. Their redox-dependent electronic states of the resulting multispin polyradicals have been characterized by VT-ESR, UV/Vis-NIR absorption and spectroelectrochemical measurements. The singlet (ΔES-T=-1.29 kcal mol-1) and a nearly degenerate singlet-triplet ground state (ΔES-T(calcd)=-0.15 kcal mol-1 and ΔES-T(exp)=0.01 kcal mol-1) were proved for diradical dications 12+2⋅ and 22+2⋅, respectively. Our work provides an experimental proof for the construction of electron-donating new chiral nanorings, and more importantly for highly charged polyradicals with potential applications in chirospintronics and organic conductors.

Host-Guest Chemistry in Binary and Ternary Complexes Utilizing π-Conjugated Carbon Nanorings

The carbon nanorings, possessing a radial π system, have garnered significant attention primarily due to their size-dependent photophysical properties and the presence of a unique curved π-conjugated cavity. This is evidenced by the rapid proliferation of publications. Furthermore, the integration of building blocks into CPP skeletons can confer [n]CPPs with novel and exceptional photophysical and electronic characteristics, as well as chiral properties and host-guest interactions, thereby augmenting the diversity of [n]CPPs. Notably, the curved π surface structures and concave cavity of carbon nanorings enable them to host aromatic or non-aromatic guests with a complementarily curved surface, resulting in interesting binary or ternary complexes. This review provides a comprehensive treatment of literature reports on binary and ternary complexes, focusing on both their host-guest interactions and properties. It is important to note that the scope of this review is limited to host-guest chemistry in binary and ternary complexes based on π-conjugated carbon nanorings.

Recent advances in circularly polarized luminescence of planar chiral organic compounds

Circularly polarized luminescence (CPL), as an important chiroptical phenomenon, can not only directly characterize excited-state structural information about chiroptical materials but also has great application prospects in 3D optical displays, information storage, biological probes, CPL lasers and so forth. Recently, chiral organic small molecules with CPL have attracted a lot of research interest because of their excellent luminescence efficiency, clear molecular structures, unique flexibility and easy functionalization. Planar chiral organic compounds make up an important class of chiral organic small molecular materials and often have rigid macrocyclic skeletons, which have important research value in the field of chiral supramolecular chemistry (e.g., chiral self-assembly and chiral host-guest chemistry). Therefore, research into planar chiral organic compounds has become a hotspot for CPL. It is time to summarize the recent developments in CPL-active compounds based on planar chirality. In this feature article, we summarize various types of CPL-active compounds based on planar chirality. Meanwhile, we overview recent research in the field of planar chiral CPL-active compounds in terms of optoelectronic devices, asymmetric catalysis, and chiroptical sensing. Finally, we discuss their future research prospects in the field of CPL-active materials. We hope that this review will be helpful to research work related to planar chiral luminescent materials and promote the development of chiral macrocyclic chemistry.

Aromaticity in Semi-Condensed Figure-Eight Molecules

Electron delocalization and aromaticity was comparatively evaluated in recently synthesized figure-eight molecules made of two condensed U-shaped polycyclic aromatic hydrocarbon moieties connected either by two single bonds or by two para-phenylene groups. The selected examples include molecules that incorporate eight-membered and sixteen-membered rings, as well as a doubly [5]helicene-bridged (1,4)cyclophane. We probe whether some electron delocalization could occur through the stereogenic single bonds in these molecules: Is aromaticity purely (semi-)local, or possibly also global in these molecules? It was concluded that the situation can go from a purely (semi-)local character when the dihedral angle at the connecting single bonds is large, such as in biphenyl, to a predominantly (semi-)local character with a minor global contribution when the dihedral angle is small, such as in the para-phenylene connectors of the [5] helicene-bridged cyclophane.

Facile synthesis and characterization of aza-bridged all-benzenoid quinoidal figure-eight and cage molecules

Synthesis of conjugated compounds with unusual shape-persistent structures remains a challenge. Herein, utilizing thermodynamically reversible intermolecular Friedel-Crafts alkylation, a dynamic covalent chemistry (DCC) reaction, we facilely synthesized a figure-eight shaped macrocycle FEM and cage molecules CATPA/CACz. X-ray crystallographic analysis confirmed the chemical geometries of tetracation FEM4+(PF6 -)4 and hexacation CACz6+(SbF6 -)6. FEM and CATPA displayed higher photoluminescence quantum yield in solid states compared to that in solution, whereas CACz gave the reverse result. DFT calculations showed that fluorescence-related frontier molecular orbital profiles are mainly localized on their arms consisting of a p-quinodimethane (p-QDM) unit and two benzene rings of triphenylamine or carbazole. Owing to their space-confined structures, variable-temperature 1H NMR measurements showed that FEM, CATPA and FEM4+ have intramolecular restricted motion of phenyl rings on their chromophore arms. Accordingly, FEM and CATPA with flexible triphenylamine subunits displayed aggregation-induced emission behavior (AIE), whereas CACz with a rigid carbazole subunits structure showed no AIE behavior.

Template Assisted One-Pot Synthesis of [2], Linear [3], and Radial [4]Catenane via Click Reaction

Design and synthesis of higher order catenane are unexpectedly complex and involve precise cooperation among the precursors overcoming competing and opposing interactions. We achieved synthesis of [2], linear [3], radial [4] in a one-pot reaction by consecutive ring closing through click reactions. This synthesis gave three isolable products due to two, four, and six-click reactions between suitable coupling partners. Yields of the isolate templated-catenane decrease from lower to higher-ordered catenane (40 %, 12 %, and 4 %), probably due to the bite angle as well as the flexibility of the reacting partners. Removal of templating cobalt(III) ion leads to the formation of fully organic [2], linear [3], and radial [4]catenane. These synthesized catenanes were purified by column chromatography and characterized by 1H-NMR, 13C-NMR, and ESI-MS spectroscopy. The synthesized catenanes have free binding sites suitable for post-functionalization and may be used for the synthesis of higher-ordered catenane.

Highly Luminescent Chiral Carbon Nanohoops via Symmetry Breaking with a Triptycene Unit: Bright Circularly Polarized Luminescence and Size-Dependent Properties

Chiral carbon nanohoops with both high fluorescence quantum yield and large luminescence dissymmetry factor are essential to the development of circularly polarized luminescence (CPL) materials. Herein, the rational design and synthesis of a series of highly fluorescent chiral carbon nanohoops TP-[8-13]CPPs via symmetry breaking with a chiral triptycene motif is reported. Theoretical calculations revealed that breaking the symmetry of nanohoops causes a unique size-dependent localization in the highest occupied molecular orbitals (HOMOs) and the lowest unoccupied molecular obtitals (LUMOs) as the increasing of sizes, which is sharply different from those of [n]cycloparaphenylenes. Photophysical investigations demonstrated that TP-[n]CPPs display size-dependent emissions with high fluorescence quantum yields up to 92.9% for TP-[13]CPP, which is the highest value among the reported chiral conjugated carbon nanohoops. The high fluorescence quantum yields are presumably attributed to both the unique acyclic, and radial conjugations and high radiative transition rates, which are further supported by theoretical investigations. Chiroptical studies revealed that chiral TP-[n]CPPs exhibit bright CPL with CPL brightness up to 100.5 M-1 cm-1 for TP-[11]CPP due to the high fluorescence quantum yield. Importantly, the investigations revealed the intrigued size-dependent properties of TP-[n]CPPs with regards to (chir)optical properties, which follow a nice linear relationship versus 1/n. Such a nice linear relationship is not observed in other reported conjugated nanohoops including CPPs.

Tuning optical properties of π-conjugated double nanohoops under external electric field stimuli-responsiveness

Carbon nanorings have attracted substantial interest from synthetic chemists due to their unique topological structures and distinct physical properties. An intriguing π-conjugated double-nanoring structure, denoted as [8]CPP-[10]cyclacene, was constructed via the integration of [8]cycloparaphenylene ([8]CPP) into [10]cyclacene. Using the external electric field stimuli-responsiveness of [8]CPP-[10]cyclacene, directional charge transfer can be induced, resulting in the emergence of intriguing properties. The effects of the external electric field in three specific directions were explored, vertically in the [8]CPP unit (Fy), vertically in the [10]cyclacene unit (Fz), and horizontally along the double nanorings diameter (Fx). Interestingly, the external electric field vertically to the [10]cyclacene unit significantly enhanced the first hyperpolarizability (βtot) compared to that vertically to the [8]CPP unit. Notably, [8]CPP-[10]cyclacene under Fx exhibited significantly larger the βtot values (1.48 × 105 a.u.) than those of vertical Fy and Fz. This work opens up a wide range of nonlinear optics, making it a compelling area to explore in the field of carbon nanomaterials.

Synthesis and Properties of Fluorenone-Containing Cycloparaphenylenes and Their Late-Stage Transformation

Cycloparaphenylenes (CPPs) are the smallest possible armchair carbon nanotubes, the properties of which strongly depend on their ring size. They can be further tuned by either peripheral functionalization or by replacing phenylene rings for other aromatic units. Here we show how four novel donor-acceptor chromophores were obtained by incorporating fluorenone or 2-(9H-fluoren-9-ylidene)malononitrile into the loops of two differently sized CPPs. Synthetically, we managed to perform late-stage functionalization of the fluorenone-based rings by high-yielding Knoevenagel condensations. The structures were confirmed by X-ray crystallographic analyses, which revealed that replacing a phenylene for a fused-ring-system acceptor introduces additional strain. The donor-acceptor characters of the CPPs were supported by absorption and fluorescence spectroscopic studies, electrochemical studies (displaying the CPPs as multi-redox systems undergoing reversible or quasi-reversible redox events), as well as by computations. The oligophenylene parts were found to comprise the electron donor units of the macrocycles and the fluorenone parts the acceptor units.

Synthesis of π-Conjugated Chiral Aza/Boracyclophanes with a meta and para Substitution

We herein describe the synthesis of a new class of axially chiral aza/boracyclophanes (BDN1, BXN1, BDB1 and BXB1) using binaphthyls as chiral building blocks and the main-group (B/N) chemistry with tunable electronic effects. All macrocycles substituted with triarylamine donors or triarylborane acceptors are strongly luminescent. These macrocycles showed two distinct meta and para π-conjugation pathways, leading to the formation of quasi figure-of-eight and square-shaped conformations. Interestingly, comparison of such structural models revealed that the former type of macrocycles BXN1 and BXB1 gave higher racemization barriers relative to the other ones. The results reported here may provide a new approach to engineer the optical stability of π-conjugated chiral macrocycles by controlling π-substitution patterns. The ring constraints induced by macrocyclization were also demonstrated to contribute to the configurational persistence as compared with the open-chain analogues p-BTT and m-BTT.

Synthesis of inter-[60]fullerene conjugates with inherent chirality

Coalescence of [60]fullerenes potentially produces hypothetical nanocarbon assemblies with non-naturally occurring topologies. Since the discovery of [60]fullerene in 1985, coalesced [60]fullerene oligomers have only been observed as transient species by transmission electron microscopy during an oligomerization process under a high electron acceleration voltage. Herein, we showcase the rational synthesis of covalent assemblies consisting of inherently chiral open-[60]fullerenes. The crystallographic analyses unveiled double-caged structures of non-conjugated and conjugated inter-[60]fullerene hybrids, in which the two [60]fullerene cages are bounds to each other through a covalent linkage. The former one further assembles via a heterochiral recognition so that four carbon cages are arranged in a tetrahedral manner both in solution and solid state. Reflecting radially-conjugated double π-surface nature, the inter-[60]fullerene conjugate exhibits strong electronic communication in its reduced states, intense absorption behavior, and chiroptical activity with a dissymmetry factor of 0.21 (at 674 nm) which breaks the record for known chiral organic molecules.

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.

Bismacrocycle: Structures and Applications

In the past half-century, macrocycles with different structures and functions, have played a critical role in supramolecular chemistry. Two macrocyclic moieties can be linked to form bismacrocycle molecules. Compared with monomacrocycle, the unique structures of bismacrocycles led to their specific recognition and assembly properties, also a wide range of applications, including molecular recognition, supramolecular self-assembly, advanced optical material construction, etc. In this review, we focus on the structure of bismacrocycle and their applications. Our goal is to summarize and outline the possible future development directions of bismacrocycle research.

Strong Chiroptical Effects in the Absorption and Emission of Macrocycles Based on the 2,5-Diaminoterephthalate Minimal Fluorophore

Chiral fluorescent macrocycles consisting of two to four units of dimethyl 2,5-diaminoterephthalate can be readily synthesized in a one-pot manner from inexpensive building blocks. Depending on the concentration, either a paracyclophane-like dimer with closely stacked benzene rings or a triangular trimer is the main product of the reaction. The macrocycles exhibit fluorescence in solution as well as in the solid state with maxima that are red-shifted with decreasing size of the macrocyclic ring and are observed at wavelengths from 590 (tetramer in solution) to 700 nm (dimer in the solid state). Chirality dictates the differential absorption and emission of circularly polarized light by these molecules. The ECD and CPL effects are particularly strong for the trimer, which is characterized by relatively large dissymmetry factors gabs =±2.8×10-3 at 531 nm and glum =±2.3×10-3 at 580 nm in n-hexane, being at the same time highly luminescent (Φfl =13.7 %). Despite the small chromophore, the circularly polarized brightness BCPL of 2.3 dm3  mol-1  cm-1 is comparable to values reported for other classes of established CPL emitters in the visible region, such as expanded helicenes or larger π-conjugated systems.

The Topology of Molecules with Twelve Fused Phenyl Rings ([12]Circulenes): Rings, Infinitenes, and Möbius Infinitenes

Following the recent preparation of infinitene (J. Am. Chem. Soc. 2022, 144, 862-871), a computational (ωB97XD/6-311G(d)) exploration of 42 isomeric compounds with 12 fused phenyl rings identified structures with linking number of zero (ring, saddle, and ribbon shapes), two (infinitene-like shape), and one (Möbius infinitene shape) is reported. An infinitene isomer composed of two [5]helicene fragments connected to two stacked phenyl rings and a Möbius infinitene isomer are identified that are more stable than the known infinitene. The energies of the structures are examined by assessing their macrocyclization (strain) energies, π-stacking, and possible aromaticity. Examples of fused phenyl molecules with linking numbers of 3, 4, 5, and 6 are shown, indicating the potential topological range that these molecules can possess.

Synthesis of π-Conjugated Chiral Organoborane Macrocycles with Blue to Near-Infrared Emissions and the Diradical Character of Cations

Highly emissive π-conjugated macrocycles with tunable circularly polarized luminescence (CPL) have sparked theoretical and synthetic interests in recent years. Herein, we report a synthetic approach to obtain new chiral organoborane macrocycles (CMC1, CMC2, and CMC3) that are built on the structurally chiral [5]helicenes and highly luminescent triarylborane/amine moieties embedded into the cyclic systems. These rarely accessible B/N-doped main-group chiral macrocycles show a unique topology dependence of the optoelectronic and chiroptical properties. CMC1 and CMC2 show a higher luminescence dissymmetry factor (g_lum) together with an enhanced CPL brightness (B_CPL) as compared with CMC3. Electronic effects were also tuned and resulted in bathochromic shifts of their emission and CPL responses from blue for CMC1 to the near-infrared (NIR) region for CMC3. Furthermore, chemical oxidations of the N donor sites in CMC1 gave rise to a highly stable radical cation (CMC1^·+SbF₆^-) and diradical dication species (CMC1^2·2+2SbF₆^-) that serve as a rare example of a positively charged open-shell chiral macrocycle.

A Fourfold Gold(I)-Aryl Macrocycle with Hyperbolic Geometry and its Reductive Elimination to a Carbon Nanoring Host

An ethylene glycol-decorated [6]cyclo-meta-phenylene (CMP) macrocycle was synthesized and utilized as a subunit to construct a fourfold Au^I ₂ -aryl metallacycle with an overall square arrangement. The corners consist of rigid dinuclear gold(I) complexes previously known to form only triangular metallacycles. The interplay between the conformational flexibility of the [6]CMP macrocycle and the rigid dinuclear gold(I) moieties enable the square geometry, as revealed by single-crystal X-ray diffraction. The formation of the gold complex shows size-selectivity compared to an alternative route using platinum(II) corner motifs. Upon reductive elimination, an all-organic ether-decorated carbon nanoring was obtained. Investigation as a host for the complexation of large guest molecules with a suitable convex π-surfaces was accomplished using isothermal NMR binding titrations. Association constants for [6]cycloparaphenylene ([6]CPP), [7]CPP, C₆₀ , and C₇₀ were determined.

Di-2,7-pyrenidecaphyrin(1.1.0.0.0.1.1.0.0.0) and Its Bis-Organopalladium Complexes: Synthesis and Chiroptical Properties

A non-aromatic expanded carbaporphyrinoid, incorporating two built-in 2,7-pyrenylene moieties was synthesized. The intrinsically labile structure was demonstrated by proton-triggered conformational changes between the figure-of-eight and quasi-Möbius conformers. Upon treatment with Pd(OAc)₂ , the reaction produces two bis-Pd^II complexes with distinct coordination modes. Metal coordination serves to fix the macrocyclic frameworks with the net result that both bis-Pd^II complexes could be resolved by high performance liquid chromatography (HPLC) on a chiral stationary phase. The isolated enantiomers showed persistent chiroptical properties as evidenced by the intense response in the circular dichroism (CD) spectra and the record high absorption dissymmetry factors (g_abs of up to 0.038) seen in the near-infrared spectral region. Moreover, the mutual interconversion of these two Pd^II complexes was found to be stereospecific and to favor the more stable isomers under weakly acidic conditions.

Synthesis of Twisted [n]Cycloparaphenylene by Alkene Insertion

Mono-alkene-inserted [n]cycloparaphenylenes 1 [(ene)-[n]CPP] with n=6, 8, and 10, mono-ortho-phenylene-inserted [6]CPP 2, and di-alkene-insertved [n]CPP 3 [(ene)₂ -[n]CPP] with n=4, 6, and 8 were synthesized by fusing CPP precursors and alkene or ortho- phenylene groups through coupling reactions. Single-crystal X-ray diffraction analyses reveal that the strips formed by the π-surfaces of 1 and 2 exhibited a Möbius topology in the solid state. While the Möbius topology in the parent 1 and 2 in solution was lost due to the free rotation of the paraphenylene unit even at low temperatures, ene-[6]CPP 4 with eight 1-pyrrolyl groups preserved the Möbius topology even in solution. Despite a twist, 1 has in-plane conjugation and possesses a unique size dependence of the electronic properties: namely, the opposite size dependency of the HOMO-LUMO energy relative to conventional π-conjugated molecules.

Efficient Detection of Nerve Agents through Carbon Nitride Quantum Dots: A DFT Approach

V-series nerve agents are very lethal to health and cause the inactivation of acetylcholinesterase which leads to neuromuscular paralysis and, finally, death. Therefore, rapid detection and elimination of V-series nerve agents are very important. Herein, we have carried out a theoretical investigation of carbon nitride quantum dots (C₂N) as an electrochemical sensor for the detection of V-series nerve agents, including VX, VS, VE, VG, and VM. Adsorption of V-series nerve agents on C₂N quantum dots is explored at M05-2X/6-31++G(d,p) level of theory. The level of theory chosen is quite adequate in systems describing non-bonding interactions. The adsorption behavior of nerve agents is characterized by interaction energy, non-covalent interaction (NCI), Bader's quantum theory of atoms in molecules (QTAIM), frontier molecular orbital (FMO), electron density difference (EDD), and charge transfer analysis. The computed adsorption energies of the studied complexes are in the range of -12.93 to -17.81 kcal/mol, which indicates the nerve agents are physiosorbed onto C₂N surface through non-covalent interactions. The non-covalent interactions between V-series and C₂N are confirmed through NCI and QTAIM analysis. EDD analysis is carried out to understand electron density shifting, which is further validated by natural bond orbital (NBO) analysis. FMO analysis is used to estimate the changes in energy gap of C₂N on complexation through HOMO-LUMO energies. These findings suggest that C₂N surface is highly selective toward VX, and it might be a promising candidate for the detection of V-series nerve agents.

Stereoselective Chiral Molecular Carbon Imides Featuring 12-Fold [5]helicenes Around Four Cores

Despite the great progress in research on molecular carbons containing multiple helicenes around one core, realizing the stereoselectivity of carbons containing multiple helicenes around more cores is still a great challenge. Herein, molecular carbon C₂₀₄ featuring 12-fold [5]helicenes around four cores was successfully constructed by using nine perylene diimide (PDI) units, and exhibits good solubility and stability. Despite 256 possible stereoisomers caused by the 12-fold [5]helicenes, we only obtained one pair of enantiomers with D₃ symmetry. There are four possible pairs of enantiomers with D₃ symmetry, namely 7A, 7B, 7C and 7D. Theoretical and experimental results verify that the obtained structure belongs to 7C, which has the lowest energy. The enantiomers can also be separated by chiral HPLC. These results suggest that choosing PDIs as building blocks can not only improve the solubility and stability but also realize the stereoselectivity and chirality of molecular carbons.

Circularly Polarized Luminescence in a Möbius Helicene Carbon Nanohoop**

We present the first helicene carbon nanoohop that integrates a [6]helicene into [7]cycloparaphenylene. The [6]helicene endows the helicene carbon nanohoop with chiroptical properties and configurational stability typical for higher helicenes, while the radially conjugated seven para‐phenylenes largely determine the optoelectronic properties. The structure of the helicene carbon nanoohop was unambiguously characterized by NMR, MS and X‐ray analysis that revealed that it possesses a topology of a Möbius strip in the solid state and in solution. The chirality transfers from the [6]helicene to the para‐phenylenes and leads to a pronounced circular dichroism and bright circularly polarized luminescence, which is affected by the structural topology of the nanohoop.

Simultaneous Detection of Circularly Polarized Luminescence and Raman Optical Activity in an Organic Molecular Lemniscate

Circularly polarized luminescence (CPL) and Raman optical activity (ROA) were observed in a single spectroscopic experiment for a purely organic molecule, an event that had so far been limited to lanthanide‐based complexes. The present observation was achieved for [16]cycloparaphenylene lemniscate, a double macrocycle constrained by a rigid 9,9′‐bicarbazole subunit, which introduces a chirality source and allows the molecule to be resolved into two configurationally stable enantiomers. Distortion of oligophenylene loops in this lemniscular structure produces a large magnetic transition dipole moment while maintaining the π‐conjugation‐induced enhancement of the Raman signal, causing the appearance of the CPL/ROA couple. A two‐photon mechanism is proposed to explain the population of the lowest‐energy excited electronic state prior to the simultaneous emission‐scattering event.

An unexpected dual-emissive luminogen with tunable aggregation-induced emission and enhanced chiroptical property

In the literature, organic materials with both aggregation-induced emission (AIE) and aggregation-caused quenching (ACQ) effects that can emit with multiple bands both in the solution and aggregated state are rarely reported. Herein we report a novel chiral dual-emissive bismacrocycle with tunable aggregation-induced emission colors. A facile four-step synthesis strategy is developed to construct this rigid bismacrocycle, (1,4)[8]cycloparaphenylenophane (SCPP[8]), which possesses a 1,2,4,5-tetraphenylbenzene core locked by two intersecting polyphenylene-based macrocycles. The luminescent behavior of SCPP[8] shows the unique characteristics of both ACQ effect and AIE effect, inducing remarkable redshift emission with near white-light emission. SCPP[8] is configurationally stable and possesses a novel shape-persistent bismacrocycle scaffold with a high strain energy. In addition, SCPP[8] displays enhanced circularly polarized luminescence properties due to AIE effect.

Organic materials with both aggregation induced emission (AIE) and aggregation-caused quenching (ACQ) effects that can emit with multiple wavelengths in the solution and aggregated state are rarely reported. Here, the authors report a chiral dual-emissive bismacrocycle which shows the unique ACQ and AIE effects inducing redshift emission with near white-light emission.

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.

Covalent nanosynthesis of fluorene-based macrocycles and organic nanogrids

Gridization is an alternative way to create macromolecules of various sizes in addition to linear and dendritic polymerization as well as cyclization. Organic nanogrids are an expanding family of macrocycle-like closed structures at the nanoscale, but with a series of well-defined extension edges and vertices. Cyclic nanogrids can be used as nanoscale building blocks for the fabrication of not only rotaxanes, catenanes, knots, 3D cages, but also nanopolymers, covalent organic frameworks (COFs), metal-organic frameworks (MOFs), and complex molecular cross-scale architectures. In this review, the history of fluorene-based macrocycles has first been explored, followed by the development of the synthetic methodologies; in particular, fluorene-based nanogrids are highlighted owing to their features and applications. Typically, fluorenes are fused arenes with a hybrid entity between tetrahedral Csp³ and Csp². Four ingenious connection modes of fluorene-based macrocycles, including 2,7-, 3,6-, 9,9-, and 2,9-linkages, fully demonstrate the geometric possibilities of the macrocycles and nanogrids. Such fluorene-based nanogrids will give birth to organic intelligence.

Infinitene: A Helically Twisted Figure-Eight [12]Circulene Topoisomer

New forms of molecular nanocarbon particularly looped polyarenes adopting various topologies contribute to the fundamental science and practical applications. Here we report the synthesis of an infinity-shaped polyarene, infinitene (1) (cyclo[c.c.c.c.c.c.e.e.e.e.e.e]dodecakisbenzene), comprising consecutively fused 12-benzene rings forming an enclosed loop with a strain energy of 60.2 kcal·mol^-1. Infinitene (1) represents a topoisomer of still-hypothetical [12]circulene, and its scaffold can be formally visualized as the outcome of the "stitching" of two homochiral [6]helicene subunits by both their ends. The synthetic strategy encompasses transformation of a rationally designed dithiacyclophane to cyclophadiene through the Stevens rearrangement and pyrolysis of the corresponding S,S'-bis(oxide) followed by the photocyclization. The structure of 1 is a unique hybrid of helicene and circulene with a molecular formula of C₄₈H₂₄, which can be regarded as an isomer for kekulene, [6,6]carbon nanobelt ([6,6]CNB), and [12]cyclacene. Infinitene (1) is a bench-stable yellow solid with green fluorescence and soluble to common organic solvents. Its figure-eight molecular structure was unambiguously confirmed by X-ray crystallography. The scaffold of 1 is significantly compressed as manifested by a remarkably shortened distance (3.152-3.192 Å) between the centroids of two π-π stacked central benzene rings and the closest C···C distance of 2.920 Å. Fundamental photophysical properties of 1 were thoroughly elucidated by UV-vis absorption and fluorescence spectroscopic studies and density functional theory calculations. Its configurational stability enabled separation of the corresponding enantiomers (P,P) and (M,M) by a chiral HPLC. Circular dichroism (CD) and circularly polarized luminescence (CPL) measurements revealed that 1 has moderate |g_CD| and |g_CPL| values.

Overcrowded Ethylene-Bridged Nanohoop Dimers: Regioselective Synthesis, Multiconfigurational Electronic States, and Global Hückel/Möbius Aromaticity

The design and preparation of molecular systems with multiple geometric and electronic configurations are the cornerstones for multifunctional materials with stimuli-responsive behaviors. We describe here the regioselective and facile synthesis of two types of overcrowded ethylene-bridged nanohoop dimers, with folded and twisted geometric structures as well as closed-shell, diradical and dication electronic structures. The strained nanohoop structures have a profound effect on the overall molecular and electronic configurations, which resulted in the destabilized diradical state. X-ray crystallographic analysis revealed the folded molecular geometry for the neutral species and twisted geometry for the dication species. The unique molecular dynamics, optical properties, and dynamic redox properties were disclosed in the solution phase by spectroscopic and electrochemical methods. Furthermore, the global Hückel and Möbius aromaticity were revealed by a combination of experimental and theoretical approaches. Our studies shed light on the design of nanohoop-incorporated multiconfigurational materials with unique topologies and functions.

Symmetry-Guided Synthesis of N,N'-Bicarbazole and Porphyrin-Based Mixed-Ligand Metal-Organic Frameworks: Light Harvesting and Energy Transfer

In the past decades, many attempts have been made to mimic the energy transfer (EnT) in photosynthesis, a key process occurring in nature that is of fundamental significance in solar fuels and sustainable energy. Metal-organic frameworks (MOFs), an emerging class of porous crystalline materials self-assembled from organic linkers and metal or metal cluster nodes, offer an ideal platform for the exploration of directional EnT phenomena. However, placing energy donor and acceptor moieties within the same framework with an atomistic precision appears to be a major synthesis challenge. In this work, we report the design and synthesis of a highly porous and photoactive N,N'-bicarbazole- and porphyrin-based mixed-ligand MOF, namely, NPF-500-H₂TCPP (NPF = Nebraska porous framework; H₂TCPP = meso-tetrakis(4-carboxyphenyl)porphyrin), where the secondary ligand H₂TCPP is incorporated precisely through the open metal sites of the equatorial plane of the octahedron cage resulting from the underlying (4,8) connected network of NPF-500. The efficient EnT process from N,N'-bicarbazole to porphyrin in NPF-500-H₂TCPP was captured by time-resolved spectroscopy and exemplified by photocatalytic oxidation of thioanisole. These results demonstrate not only the capability of NPF-500 as the scaffold to precisely arrange the donor-acceptor assembly for the EnT process but also the potential to directly utilize the EnT process for photocatalytic applications.

A Conjugated Figure-of-Eight Oligoparaphenylene Nanohoop with Adaptive Cavities Derived from Cyclooctatetrathiophene Core

A fully conjugated figure-of-eight nanohoop is presented with facile synthesis. The molecule's lemniscular skeleton features the combination of two strained oligoparaphenylene loops and a flexible cyclooctatetrathiophene core. Its rigid yet guest-adaptive cavities enable the formation of the peanut-like 1:2 host-guest complexes with C₆₀ or C₇₀ , which have been confirmed by X-ray crystallography and characterized in solution. Further computational studies suggest notable geometric variations and non-covalent interactions of the cavities upon binding with different fullerenes, as well as overall conjugation comparable to cycloparaphenylenes.

Helical Oligophenylene Linked with [2.2]Paracyclophane: Stereogenic π-Conjugated Dye for Highly Emissive Chiroptical Properties

A stereogenic π-system based on dimer (2) and trimer (3) of [2.2]paracyclophane (PC) and biphenyl was prepared and its structural, photophysical, and chiroptical properties were investigated. X-ray analysis revealed that the quaterphenyl moieties in 2 adopt a double helical structure anchoring [2.2]PC from both sides. Furthermore, 3 forms a isosceles triangle structure with a large chiral cavity. A homodesmotic reaction using DFT calculations revealed that 2 has a larger strain energy than 3 owing to its highly twisted phenylene linkers. Electronic and circular dichroic (CD) spectra were recorded in CH₂ Cl₂ solution. The spectra of both 2 and 3 are similar, and their longest absorption band accompanying a remarkable Cotton effect is attributed to the transition from HOMO to LUMO, which is delocalized to the quaterphenyl moiety. These compounds exhibit fairly high fluorescence quantum yields (ϕ=0.70-0.83) and moderate dissymmetry factor (|g_CPL |=1.6×10^-3 ) in circularly polarized luminescence (CPL).

Fullerene Wires Assembled Inside Carbon Nanohoops

Carbon-nanohoop structures featuring one or more round-shaped cavities represent ideal supramolecular hosts for spherical fullerenes, with potential to form host-guest complexes that perform as organic semiconductors in the solid state. Due to the tight complexation between the shape-complementary hosts and guests, carbon nanohoops have the potential to shield fullerenes from water and oxygen, known to perturb the electron-transport process. Many nanohoop receptors have been found to form host-guest complexes with fullerenes. However, there is only a little or no control over the long-range order of encapsulated fullerenes in the solid state. Consequently, the potential of these complexes to perform as organic semiconductors is rarely evaluated. Herein, we present a survey of all known nanohoop-fullerene complexes, for which the solid-state structures were obtained. We discuss and propose instances where the inclusion fullerene guests form discrete supramolecular wires, which might open up possibilities for their use in electronic devices.

Cycloparaphenylene Double Nanohoop: Structure, Lamellar Packing, and Encapsulation of C60 in the Solid State

A new member of the cycloparaphenylene double-nanohoop family was synthesized. Its π-framework features two oval cavities that display different shapes depending on the crystallization conditions. Incorporation of the peropyrene bridge within the nanoring cycles via bay-regions alleviates steric effects and thus allows 1:1 complexation with C₆₀ in the solid state. This nanocarbon adopts a lamellar packing motif, and our results suggest that the structural adjustment of this double nanohoop could enable its use in supramolecular and semiconductive materials.

Synthesis and Chiral Resolution of Twisted Carbon Nanobelts

Twisted carbon nanobelts could display persistent chirality, which is desirable for material applications, but their synthesis is very challenging. Herein, we report the successful synthesis and chiral resolution of such a kind of molecules (1-H and 1) with a figure-eight configuration. 1-H was synthesized first by macrocyclization through Suzuki coupling reaction followed by benzannulation via Bi(OTf)₃-mediated cyclization reaction of vinyl ether. Oxidative dehydrogenation of 1-H gave the fully π-conjugated 1. Their twisted structures were confirmed by X-ray crystallographic analysis and calculations, and they can be resolved by chiral high-performance liquid chromatography. The isolated enantiomers showed persistent chiroptical properties according to the circular dichroism measurements, with moderate |g_abs| values (0.0016 for 1-H and 0.005-0.007 for 1). Their photophysical properties were also briefly studied.