Large π-Extended and Curved Carbon Nanorings as Carbon Nanotube Segments

Multi-heteroatom doped nanographenes: enhancing photosensitization capacity by forming an electron donor-acceptor architecture

Systematically tuning and optimizing the properties of synthetic nanographenes (NGs) is particularly important for NG applications in diverse areas. Herein, by devising novel electron donor-acceptor (D-A) type structures, we reported a series of multi-heteroatom-doped NGs possessing an electron-rich chalcogen and electron-deficient pyrimidine or pyrimidinium rings. Comprehensive experimental and theoretical investigations revealed significantly different physical, optical, and energetic properties compared to the non-doped HBC or chalcogen-doped, non-D-A analogues. Some intriguing properties of the new NGs such as unique electrostatically oriented molecular stacking, red-shifted optical spectra, solvatochromism, and enhanced triplet excitons were observed due to the formation of the D-A electron pattern. More importantly, these D-A type structures can serve as photosensitizers to generate efficiently reactive-oxygen species (ROS), and the structure-related photosensitization capacity that strengthens the electron transfer (ET) process leads to significantly enhanced ROS which was revealed by experimental and calculated studies. As a result, the cell-based photodynamic therapy (PDT) indicated that the cationic NG 1-Me+ is a robust photosensitizer with excellent water-solubility and biocompatibility.

π-Conjugated Nanohoops: A New Generation of Curved Materials for Organic Electronics

Nanohoops, cyclic association of π-conjugated systems to form a hoop-shaped molecule, have been widely developed in the last 15 years. Beyond the synthetic challenge, the strong interest towards these molecules arises from their radially oriented π-orbitals, which provide singular properties to these fascinating structures. Thanks to their particular cylindrical arrangement, this new generation of curved molecules have been already used in many applications such as host-guest complexation, biosensing, bioimaging, solid-state emission and catalysis. However, their potential in organic electronics has only started to be explored. From the first incorporation as an emitter in a fluorescent organic light emitting diode (OLED), to the recent first incorporation as a host in phosphorescent OLEDs or as charge transporter in organic field-effect transistors and in organic photovoltaics, this field has shown important breakthroughs in recent years. These findings have revealed that curved materials can play a key role in the future and can even be more efficient than their linear counterparts. This can have important repercussions for the future of electronics. Time has now come to overview the different nanohoops used to date in electronic devices in order to stimulate the future molecular designs of functional materials based on these macrocycles.

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.

BINOL-Based Chiral Macrocycles and Cages

Chirality, a fundamental principle in chemistry, biology, and medicine, is prevalent in nature and in organisms. Chiral molecules, such as DNA, RNA, and proteins, are crucial in biomolecular synthesis, as well as in the development of functional materials. Among these, 1,1'-binaphthyl-2,2'-diol (BINOL) stands out for its stable chiral configuration, versatile functionality, and commercial availability. BINOL is widely employed in asymmetric catalysis and chiral materials. This review mainly focuses on recent research over the past five years concerning the use of BINOL derivatives for constructing chiral macrocycles and cages. Their contributions to chiral luminescence, enantiomeric separation, transmembrane transport, and asymmetric catalysis were examined.

Enantiomerically Resolvable Inherent Chirality Induced by Strong Para-Steric Hindrance in Cycloparaphenylene-Based Carbon Nanohoops

The chemical modification of the achiral carbon nanohoops to break the symmetry will result in inherently chiral structures with interesting optical properties. Herein, we report two novel π-extended chiral macrocycles, cyclo[10]paraphenylene-pyrene ([10]CPP-2Pyrene) and cyclo[10]paraphenylene-hexa-peri-hexabenzocoronene ([10]CPP-2HBC). The large substituents on the nanohoop peripheries effectively prevented free rotation and the racemization process. The conformation of each enantiomer is stable enough to be resolved by recycling HPLC.

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.

Cyclooctatetraene-Embedded Carbon Nanorings

With the prosperity of the development of carbon nanorings, certain topologically or functionally unique units-embedded carbon nanorings have sprung up in the past decade. Herein, we report the facile and efficient synthesis of three cyclooctatetraene-embedded carbon nanorings (COTCNRs) that contain three (COTCNR1 and COTCNR2) and four (COTCNR3) COT units in a one-pot Yamamoto coupling. These nanorings feature hoop-shaped segments of Gyroid (G-), Diamond (D-), and Primitive (P-) type carbon schwarzites. The conformations of the trimeric nanorings COTCNR1 and COTCNR2 are shape-persistent, whereas the tetrameric COTCNR3 possesses a flexible carbon skeleton which undergoes conformational changes upon forming host-guest complexes with fullerenes (C60 and C70), whose co-crystals may potentially serve as fullerene-based semiconducting supramolecular wires with electrical conductivities on the order of 10-7 S cm-1 (for C60⊂COTCNR3) and 10-8 S cm-1 (for C70⊂COTCNR3) under ambient conditions. This research not only describes highly efficient one-step syntheses of three cyclooctatetraene-embedded carbon nanorings which feature hoop-shaped segments of distinctive topological carbon schwarzites, but also demonstrates the potential application in electronics of the one-dimensional fullerene arrays secured by COTCNR3.

A Conjugated Phenylene Nanocage with a Guest-Adaptive Deformable Cavity

The highly strained, phenylene-derived organic cages are typically regarded as very rigid entities, yet their deformation potential and supramolecular properties remain underexplored. Herein, we report a pliable conjugated phenylene nanocage by synergistically merging rigid and flexible building blocks. The anisotropic cage molecule contains branched phenylene chains capped by a calix[6]arene moiety, the delicate conformational changes of which endow the cage with a remarkably deformable cavity. When complexing with fullerene guests, the cage showcases excellent guest-adaptivity, with its cavity volume capable of swelling by as much as 85 %.

Tethered Helical Ladder-Type Aromatic Lactams

Tethered nonplanar aromatics (TNAs) make up an important class of nonplanar aromatic compounds showing unique features. However, the knowledge on the synthesis, structures, and properties of TNAs remains insufficient. In this work, a new type of TNAs, the tethered aromatic lactams, is synthesized via Pd-catalyzed consecutive intramolecular direct arylations. These molecules possess a helical ladder-type conjugated system of up to 13 fused rings. The overall yields ranged from 3.4 to 4.3%. The largest of the tethered aromatic lactams, 6L-Bu-C14, demonstrates a guest-adaptive hosting capability of TNAs for the first time. When binding fullerene guests, the cavity of 6L-Bu-C14 became more circular to better accommodate spherical fullerene molecules. The host-guest interaction is thoroughly studied by X-ray crystallography, theoretical calculations, fluorescence titration, and nuclear magnetic resonance (NMR) titration experiments. 6L-Bu-C14 shows stronger binding with C70 than with C60 due to the better convex-concave π-π interaction. P and M enantiomers of all tethered aromatic lactams show distinct and persistent chiroptical properties and demonstrate the potential of chiral TNAs as circularly polarized luminescence (CPL) emitters.

Appending Coronene Diimide with Carbon Nanohoops Allows for Rapid Intersystem Crossing in Neat Film

The development of innovative triplet materials plays a significant role in various applications. Although effective tuning of triplet formation by intersystem crossing (ISC) has been well established in solution, the modulation of ISC processes in the solid state remains a challenge due to the presence of other exciton decay channels through intermolecular interactions. The cyclic structure of cycloparaphenylenes (CPPs) offers a unique platform to tune the intermolecular packing, which leads to controllable exciton dynamics in the solid state. Herein, by integrating an electron deficient coronene diimide (CDI) unit into the CPP framework, a donor-acceptor type of conjugated macrocycle (CDI-CPP) featuring intramolecular charge-transfer (CT) interaction was designed and synthesized. Effective intermolecular CT interaction resulting from a slipped herringbone packing was confirmed by X-ray crystallography. Transient spectroscopy studies showed that CDI-CPP undergoes ISC in both solution and the film state, with triplet generation time constants of 4.5 ns and 238 ps, respectively. The rapid triplet formation through ISC in the film state can be ascribed to the cooperation between intra- and intermolecular charge-transfer interactions. Our results highlight that intermolecular CT interaction has a pronounced effect on the ISC process in the solid state, and shed light on the use of the characteristic structure of CPPs to manipulate intermolecular CT interactions.

Two-dimensional radial-π-stacks in solution

Highly organized π-aggregate architectures can strongly affect electronic couplings, leading to important photophysical behaviors. With the escalating interest in two-dimensional (2D) materials attributed to their exceptional electronic and optical characteristics, there is growing anticipation that 2D radial-π-stacks built upon radial π-conjugation nanorings, incorporating intra- and inter-ring electronic couplings within the confines of a 2D plane, will exhibit superior topological attributes and distinct properties. Despite their immense potential, the design and synthesis of 2D π-stacks have proven to be a formidable challenge due to the insufficient π-π interactions necessary for stable stacking. In this study, we present the successful preparation of single-layer 2D radial-π-stacks in a solution. Pillar-shaped radially π-conjugated [4]cyclo-naphthodithiophene diimide ([4]C-NDTIs) molecules were tetragonally arranged via in-plane intermolecular π-π interactions. These 2D π-stacks have a unique topology that differs from that of conventional 1D π-stacks and exhibit notable properties, such as acting as a 2D template capable of absorbing C60 guest molecules and facilitating the formation of 2D radial-π-stacks comprising [4]C-NDTI-C60 complexes, rapid exciton delocalization across the 2D plane, and efficient excitation energy funneling towards a trap.

Tris-Azo Triangular Paraphenylenes: Synthesis and Reversible Interconversion into Radial π-Conjugated Macrocycles

We report the synthesis of cycloparaphenylene derivatives featuring tris-azo groups. The smaller derivative, [3]cycloazobenzene, adopts a triangular all-cis form and exhibits thermally and photochemically stable characteristics due to significant ring strain as well as symmetric Kagome-patterned crystal packing. In contrast, the as-synthesized [3]cycloazobenzene with three biphenylene bridges adopts a triangular all-cis form, which undergoes photoinduced isomerization, leading to a photostationary state. Interestingly, the addition of an excess of acid selectively leads to the formation of an all-trans form. DFT calculations reveal that the interconversion from a triangular to a circular shape correlates with an increase in HOMO and a decrease in LUMO, characteristics intrinsic to radial π-conjugated systems.

Carbon Nanomaterial Fluorescent Probes and Their Biological Applications

Fluorescent carbon nanomaterials have broadly useful chemical and photophysical attributes that are conducive to applications in biology. In this review, we focus on materials whose photophysics allow for the use of these materials in biomedical and environmental applications, with emphasis on imaging, biosensing, and cargo delivery. The review focuses primarily on graphitic carbon nanomaterials including graphene and its derivatives, carbon nanotubes, as well as carbon dots and carbon nanohoops. Recent advances in and future prospects of these fields are discussed at depth, and where appropriate, references to reviews pertaining to older literature are provided.

Soluble Nanographene C222: Synthesis and Applications for Synergistic Photodynamic/Photothermal Therapy

Nanographene C222, which consists of a planar graphenic plane containing 222 carbon atoms, holds the record as the largest planar nanographene synthesized to date. However, its complete insolubility makes the processing of C222 difficult. Here we addressed this issue by introducing peripheral substituents perpendicular to the graphene plane, effectively disrupting the interlayer stacking and endowing C222 with good solubility. We also found that the electron-withdrawing substituents played a crucial role in the cyclodehydrogenation process, converting the dendritic polyphenylene precursor to C222. After disrupting the interlayer stacking, the introduction of only a few peripheral carboxylic groups allowed C222 to dissolve in phosphate buffer saline, reaching a concentration of up to 0.5 mg/mL. Taking advantage of the good photosensitizing and photothermal properties of the inner C222 core, the resulting water-soluble C222 emerged as a single-component agent for both photothermal and photodynamic tumor therapy, exhibiting an impressive tumor inhibition rate of 96%.

Noncovalent Modification of Cycloparaphenylene by Catenane Formation Using an Active Metal Template Strategy

The active metal template (AMT) strategy is a powerful tool for the formation of mechanically interlocked molecules (MIMs) such as rotaxanes and catenanes, allowing the synthesis of a variety of MIMs, including π-conjugated and multicomponent macrocycles. Cycloparaphenylene (CPP) is an emerging molecule characterized by its cyclic π-conjugated structure and unique properties. Therefore, diverse modifications of CPPs are necessary for its wide application. However, most CPP modifications require early stage functionalization and the direct modification of CPPs is very limited. Herein, we report the synthesis of a catenane consisting of [9]CPP and a 2,2'-bipyridine macrocycle as a new CPP analogue that contains a reliable synthetic scaffold enabling diverse and concise post-modification. Following the AMT strategy, the [9]CPP-bipyridine catenane was successfully synthesized through Ni-mediated aryl-aryl coupling. Catalytic C-H borylation/cross-coupling and metal complexation of the bipyridine macrocycle moiety, an effective post-functionalization method, were also demonstrated with the [9]CPP-bipyridine catenane. Single-crystal X-ray structural analysis revealed that the [9]CPP-bipyridine catenane forms a tridentated complex with an Ag ion inside the CPP ring. This interaction significantly enhances the phosphorescence lifetime through improved intermolecular interactions.

Functionalization of Pentacene: A Facile and Versatile Approach to Contorted Polycyclic Aromatic Hydrocarbons

In this work, a facile and versatile strategy for the synthesis of contorted polycyclic aromatic hydrocarbons (PAHs) starting from the functionalized pentacene was established. A series of novel PAHs 1-4 and their derivatives were synthesized through a simple two-step synthesis procedure involving an intramolecular reductive Friedel-Crafts cyclization of four newly synthesized pentacene aldehydes 5-8 as a key step. All the molecules were confirmed by single-crystal X-ray diffraction and their photophysical and electrochemical properties were studied in detail. Interestingly, the most striking feature of 1-4 is their highly contorted carbon structures and the accompanying helical chirality. In particular, the optical resolution of 2 was successfully achieved by chiral-phase HPLC, and the enantiomers were characterized by circular dichroism and circularly polarized luminescence spectroscopy. Despite the highly nonplanar conformations, these contorted PAHs exhibited emissive properties with moderate-to-good fluorescence quantum yields, implying the potential utility of this series PAHs as high-quality organic laser dyes. By using a self-assembly method with the help of epoxy resin, a bottle microlaser based on 3 a was successfully illustrated with a lasing wavelength of 567.8 nm at a threshold of 0.3 mJ/cm2 . We believe that this work will shed light on the chemical versatility of pentacene and its derivatives in the construction of novel functionalized PAHs.

Design and Synthesis of New Type of Macrocyclic Architectures Used for Optoelectronic Materials and Supramolecular Chemistry

Supramolecular chemistry has received much attention for decades. Macrocyclic architectures as representative receptors play a vital role in supramolecular chemistry and are applied in many fields such as supramolecular assembly and host-guest recognition. However, the classical macrocycles generally lack functional groups in the scaffolds, which limit their further applications, especially in optoelectronic materials. Therefore, developing a new design principle is not only essential to better understand macrocyclic chemistry and the supramolecular behaviors, but also further expand their applications in many research fields. In recent years, the doping compounds with main-group heteroatoms (B, N, S, O, P) into the carbon-based π-conjugated macrocycles offered a new strategy to build macrocyclic architectures with unique optoelectronic properties. In particular, the energy gaps and redox behavior can be effectively tuned by incorporating heteroatoms into the macrocyclic scaffolds. In this Minireview, we briefly summarize the design and synthesis of new macrocycles, and further discuss the related applications in optoelectronic materials and supramolecular chemistry.

Chalcogen-doped, (seco)-hexabenzocoronene-based nanographenes: synthesis, properties, and chalcogen extrusion conversion

A series of chalcogen-doped nanographenes (NGs) and their oxides are described. Their molecular design is conceptually based on the insertion of different chalcogens into the hexa-peri-hexabenzocoronene (HBC) backbone. All the NGs adopt nonplanar conformations, which would show better solubility compared to planar HBC. Except for the oxygen-doped, saddle-shaped NG, the insertion of large chalcogens like sulfur and selenium leads to a seco-HBC-based, helical geometry. All the three-dimensional structures are unambiguously confirmed by single-crystal X-ray diffractometry. Their photophysical properties including UV-vis absorption, fluorescence, chiroptical, charge distribution, and orbital gaps are investigated experimentally or theoretically. The properties of each structure are significantly affected by the doped chalcogen and its related oxidative state. Notably, upon heating or adding an acid, the selenium-doped NG or its oxide undergoes a selenium extrusion reaction to afford seco-HBC or HBC quantitatively, which can be treated as precursors of hydrocarbon HBCs.

Photoinduced electron transfer in [10]CPP⊃C60 oligomers with stable and well-defined supramolecular structures

Recent synthesis of a new type of polymer containing conjugated cycloparaphenylene (CPP) macrocycles interconnected by a linear conjugated backbone opens up great potential of cyclic π-conjugated materials in organic photovoltaics. In this work, I report a theoretical study of the ground and excited state properties of such polymers and investigate an effect of inclusion of fullerene molecules into polymer chains. MD simulations reveal that oligomers ([10]CPP_Fused⊃C60)24 and ([10]CPP_Fused⊃C60)32 with π-extended CPPs tend to form stable, helix-like structures. I show that photoinduced electron transfer from the CPP-based polymer to C60 fullerene is favorable and occurs on a nanosecond time scale. The hole- and excess-electron transfer rates are found to be significantly higher than the corresponding charge recombination rates.

Construction of hexabenzocoronene-based chiral nanographenes

The past decade witnessed remarkable success in synthetic molecular nanographenes. Encouraged by the widespread application of chiral nanomaterials, the design, and construction of chiral nanographenes is a hot topic recently. As a classic nanographene unit, hexa-peri-hexabenzocoronene generally serves as the building block for nanographene synthesis. This review summarizes the representative examples of hexa-peri-hexabenzocoronene-based chiral nanographenes.

Alternating behavior in furan-acetylene macrocycles reveals the size-dependency of Hückel's rule in neutral molecules

Aromaticity can be assigned by Hückel's rule, which predicts that planar rings with delocalized (4n + 2) π-electrons are aromatic, whereas those with 4n π-electrons are antiaromatic. However, for neutral rings, the maximal value of "n" to which Hückel's rule applies remains unknown. Large macrocycles exhibiting global ring current can serve as models for addressing this question, but the global ring current are often overshadowed in these molecules by the local ring current of the constituent units. Here, we present a series of furan-acetylene macrocycles, ranging from the pentamer to octamer, whose neutral states display alternating contributions from global aromatic and antiaromatic ring currents. We find that the odd-membered macrocycles display global aromatic characteristics, whereas the even-membered macrocycles display contributions from globally antiaromatic ring current. These factors are expressed electronically (oxidation potentials), optically (emission spectra), and magnetically (chemical shifts), and DFT calculations predict global ring current alternations up to 54 π-electrons.

Two Rings Around One Ball: Stability and Charge Localization of [1 : 1] and [2 : 1] Complex Ions of [10]CPP and C60/70 [ *]

We investigate the gas-phase chemistry of noncovalent complexes of [10]cycloparaphenylene ([10]CPP) with C₆₀ and C₇₀ by means of atmospheric pressure photoionization and electrospray ionization mass spectrometry. The literature-known [1 : 1] complexes, namely [10]CPP⊃C₆₀ and [10]CPP⊃C₇₀ , are observed as radical cations and anions. Their stability and charge distribution are studied using energy-resolved collision-induced dissociation (ER-CID). These measurements reveal that complexes with a C₇₀ core exhibit a greater stability and, on the other hand, that the radical cations are more stable than the respective radical anions. Regarding the charge distribution, in anionic complexes charges are exclusively located on C₆₀ or C₇₀ , while the charges reside on [10]CPP in the case of cationic complexes. [2 : 1] complexes of the ([10]CPP₂ ⊃C_60/70 )⁺ ⋅^/- ⋅ type are observed for the first time as isolated solitary gas-phase species. Here, C₆₀ -based [2 : 1] complexes are less stable than the respective C₇₀ analogues. By virtue of the high stability of cationic [1 : 1] complexes, [2 : 1] complexes show a strongly reduced stability of the radical cations. DFT analyses of the minimum geometries as well as molecular dynamics calculations support the experimental data. Furthermore, our novel gas-phase [2 : 1] complexes are also found in 1,2-dichlorobenzene. Insights into the thermodynamic parameters of the binding process as well as the species distribution are derived from isothermal titration calorimetry (ITC) measurements.

Synthesis and Physical Properties of a Perylene Diimide-Embedded Chiral Conjugated Macrocycle

Herein, we report the facile synthesis and properties of a chiral perylene diimide (PDI)-embedded conjugated macrocycle (cyclo[6]paraphenylene-1,7-perylene diimide, [6]CPP-PDI_1,7) by Pd-catalyzed Suzuki coupling and a subsequent reductive aromatization reaction in two steps. The PDI-embedded conjugated macrocycle showed a significant redshift (>110 nm for absorption) compared to the PDI molecule. Moreover, efficient resolution of chiral enantiomers with (P)/(M)-[6]CPP-PDI_1,7 was achieved by high-performance liquid chromatography, and their chiral properties were investigated by circular dichroism spectroscopy. The realization of [6]CPP-PDI_1,7 expands the scope of the precise synthesis of PDI-embedded chiral conjugated macrocycles and explores its unique physical properties.

Azepine-Embedded Seco-Hexabenzocoronene-Based Helix Nanographenes: Access to Modification of the Core by N-H Functionalization

Contorted polycyclic aromatic hydrocarbons (PAHs) or nanographenes (NGs) have received increasing attention and are mostly prepared by "bottom-up" strategies. Apparently, systematically tuning the properties of NGs for application is important but challenging. Here, a new type of helix, azepine-embedded NGs, were designed and synthesized by the introduction of NH into the hexa-peri-hexabenzocoronene (HBC) core. We demonstrate that this nitrogen-doped NG can be functionalized via N-H derivatization. Through modifications to the NH site with a chiral auxiliary reagent, optical resolution of the chiral NG was achieved. Meanwhile, it was found that by introducing various aryl groups with electron-donating or electron-withdrawing substituents, the emission intensity and the fluorescence mechanism can be modulated. Compared to the original NH-containing NG, the modified derivative exhibited improved fluorescence efficiency and tunable emission wavelength. A functionalized structure of benzoic acid with considerably improved fluorescence efficiency, hydrophilicity, and membrane permeability to stain the live cells was proved.

Cleavage of non-polar C(sp2)‒C(sp2) bonds in cycloparaphenylenes via electric field-catalyzed electrophilic aromatic substitution

Electrophilic aromatic substitution (EAS) is one of the most fundamental reactions in organic chemistry. Using an oriented external electric field (OEEF) instead of traditional reagents to tune the EAS reactivity can offer an environmentally friendly method to synthesize aromatic compounds and hold the promise of broadening its scope. Despite these advantages, OEEF catalysis of EAS is difficult to realize, due to the challenge of microscopically orienting OEEF along the direction of electron reorganizations. In this work, we demonstrate OEEF-catalyzed EAS reactions in a series of cycloparaphenylenes (CPPs) using the scanning tunneling microscope break junction (STM-BJ) technique. Crucially, the unique radial π-conjugation of CPPs enables a desired alignment for the OEEF to catalyze the EAS with Au STM tip (or substrate) acting as an electrophile. Under mild conditions, the OEEF-catalyzed EAS reactions can cleave the inherently inert C(sp²)-C(sp²) bond, leading to high-yield (~97%) formation of linear oligophenylenes terminated with covalent Au-C bonds. These results not only demonstrate the feasibility of OEEF catalysis of EAS, but also offer a way of exploring new mechanistic principles of classic organic reactions aided by OEEF.

Metallofullertube: From Tubular Endohedral Structures to Properties

Metallofullertubes are endohedral metallofullerenes with tubular fullerene cage possessing the segment of carbon nanotubes. Metallofullertubes have endohedral metal atom, fullerene cap and nanotube segment. Therefore, it is conceivable that this new kind of molecular materials would bring on many unexpected properties. In recent years, several pioneer metallofullertubes have been successfully reported, such as La₂ @D₅ (450)-C₁₀₀ , Ce₂ @D₅ (450)-C₁₀₀ , Sm₂ @D_3d (822)-C₁₀₄ . Apart from the great effort to synthesize molecules and determine their structures, the physical and chemical properties of metallofullertubes are still waiting to be explored. In this minireview, we revisit the structures of reported metallofullertubes, and then we highlight their electronic and supramolecular properties. Finally, some perspectives for the development of metallofullertubes are also discussed.

Magnetically Induced Current Densities in π-Conjugated Porphyrin Nanoballs

Magnetically induced current densities (MICDs) of Zn-porphyrinoid nanostructures have been studied at the density functional theory level using the B3LYP functional and the def2-SVP basis set. Six of the studied Zn-porphyrinoid nanostructures consist of two crossing porphyrinoid belts, and one is a porphyrinoid nanoball belonging to the octahedral (O) point group. The Zn-porphyrin units are connected to each other via butadiyne linkers as in a recently synthesized porphyrinoid structure resembling two crossed belts. The MICDs are calculated using the gauge-including magnetically induced current method. Current-density pathways and their strengths were determined by numerically integrating the MICD passing through selected planes that cross chemical bonds or molecular rings. The current-density calculations show that the studied neutral molecules are globally nonaromatic but locally aromatic sustaining ring currents only in the individual porphyrin rings or around two neighboring porphyrins. The ring-current strengths of the individual porphyrin rings are 20% weaker than in Zn-porphyrin, whereas oxidation leads to globally aromatic cations sustaining ring currents that are somewhat stronger than for Zn-porphyrin.

Carbon Surface Chemistry: New Insight into the Old Story

The enormous complexity of the carbon material family has provoked a phenomenological approach to develop its potential in different applications. Although the electronic, chemical, mechanical, and magnetic properties of carbon materials have been widely discussed based on defect control engineering, there is still a lack of fundamental understanding of the carbon surface chemistry, which leads to many controversial conclusions. Here, by analyzing various defects on carbon surface, some commonly neglected aspects and misunderstandings in this field are pointed out, clarifying how surface chemistry affects the chemical behaviors of carbon in some specific chemical reactions. With this full-scale consideration of the carbon surface chemistry, the behaviors of carbon materials with various functions can be well defined, which is indispensable for their scalable applications. Perspectives on future developments of carbon surface chemistry are also provided to enable practically accessible design of advanced carbon in those applications.

Intense Molar Circular Dichroism in Fully Conjugated All-Carbon Macrocyclic 1,3-Butadiyne Linked pseudo-meta [2.2]Paracyclophanes

The synthetic access to macrocyclic molecular topologies with interesting photophysical properties has greatly improved thanks to the successful implementation of organic and inorganic corner units. Based on recent reports, we realized that pseudo-meta [2.2]paracyclophanes (PCPs) might serve as optimal corner units for constructing 3D functional materials, owing to their efficient electronic communication, angled substituents and planar chirality. Herein, we report the synthesis, characterization and optical properties of four novel all-carbon enantiopure macrocycles bearing three to six pseudo-meta PCPs linked by 1,3-butadiyne units. The macrocycles were obtained by a single step from enantiopure, literature-known dialkyne pseudo-meta PCP and were unambiguously identified and characterized by state of the art spectroscopic methods and in part even by x-ray crystallography. By comparing the optical properties to relevant reference compounds, it is shown that the pseudo-meta PCP subunit effectively elongates the conjugated system throughout the macrocyclic backbone, such that already the smallest macrocycle consisting of only three subunits reaches a polymer-like conjugation length. Additionally, it is shown that the chiral pseudo-meta PCPs induce a remarkable chiroptical response in the respective macrocycles, reaching unprecedented high molar circular dichroism values for all-carbon macrocycles of up to 1307 L mol^-1  cm^-1 .

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.

Gram-scale synthesis of a covalent nanocage that preserves the redox properties of encapsulated fullerenes

Discrete nanocages provide a way to solubilize, separate, and tune the properties of fullerenes, but these 3D receptors cannot usually be synthesized easily from inexpensive starting materials, limiting their utility. Herein, we describe the first fullerene-binding nanocage (Cage⁴⁺) that can be made efficiently on a gram scale. Cage⁴⁺ was prepared in up to 57% yield by the formation of pyridinium linkages between complemantary porphyrin components that are themselves readily accessible. Cage⁴⁺ binds C₆₀ and C₇₀ with large association constants (>10⁸ M⁻¹), thereby solubilizing these fullerenes in polar solvents. Fullerene association and redox-properties were subsequently investigated across multiple charge states of the host-guest complexes. Remarkably, neutral and singly reduced fullerenes bind with similar strengths, leaving their 0/1⁻ redox couples minimally perturbed and fully reversible, whereas other hosts substantially alter the redox properties of fullerenes. Thus, C₆₀@Cage⁴⁺ and C₇₀@Cage⁴⁺ may be useful as solubilized fullerene derivatives that preserve the inherent electron-accepting and electron-transfer capabilities of the fullerenes. Fulleride dianions were also found to bind strongly in Cage⁴⁺, while further reduction is centered on the host, leading to lowered association of the fulleride guest in the case of C₆₀²⁻.

This report describes the first gram-scale synthesis of a nanocage that can host fullerenes (C₆₀ and C₇₀). The redox properties of the fullerenes are preserved in this host, enabling characterization of complexes with fulleride anions and dianions.

Magnetically Induced Current Densities in Zinc Porphyrin Nanoshells

The molecular structures of porphyrinoid cages were obtained by constructing small polyhedral graphs whose vertices have degree-4. The initial structures were then fully optimized at the density functional theory (DFT) level using the generalized gradient approximation. Some of polyhedral vertices were replaced with Zn–porphyrin units and their edges were replaced with ethyne or butadiyne bridges or connected by fusing two neighboring Zn–porphyrin units. Molecule 1 is an ethyne-bridge porphyrinoid nanotube, whose ends are sealed with a Zn–porphyrin. Molecule 2 is the corresponding open porphyrinoid nanotube. Molecule 3 is a clam-like porphyrinoid cage, whose shells consist of fused Zn–porphyrins, and the two halves are connected via butadiyne bridges. Molecule 4 is a cross-belt of fused Zn–porphyrins, and molecule 5 is a cross-belt of Zn–porphyrins connected with butadiyne bridges. The magnetically induced current density of the optimized porphyrinoid cages was calculated for determining the aromatic character, the degree of aromaticity and the current-density pathways. The current-density calculations were performed at the DFT level with the gauge—including magnetically induced currents (GIMIC) method using the B3LYP hybrid functional and def2-SVP basis sets. Calculations of the current densities show that molecule 2 sustains a paratropic ring current around the nanotube, whereas sealing the ends as in molecule 1 leads to an almost nonaromatic nanotube. Fusing porphyrinoids as in molecules 3 and 4 results in complicated current-density pathways that differ from the ones usually appearing in porphyrinoids. The aromatic character of molecules 4 and 5 changes upon oxidation. The neutral molecule 4 is antiaromatic, whereas the dication is nonaromatic. Molecule 5 is nonaromatic, and its dication is aromatic.

Modular synthesis, racemization pathway, and photophysical properties of asymmetrically substituted cycloparaphenylenes

The racemization pathways of asymmetrically substituted cycloparaphenylenes analysed by transition-state calculations (TS) revealed size-dependent rotation barriers.

Molecular Möbius Strips: Twist for A Bright Future

Attributed to their unique structural features and associated intriguing properties, molecular Möbius strips have attracted considerable attention. However, the precise synthesis of such attractive molecules remains a great challenge. Recently,...

Azepine- or Oxepine-embedded Double Saddle-Helix Nanographenes

The azepine- and oxepine-embedded polycyclic aromatic hydrocarbons (PAH) 1-3, as the hexa-peri-hexabenzocoronene (HBC)-based nanographenes (NG) were designed and synthesized by Diels-Alder reaction of cyclic alkene with tetrachlorothiophene-S,S-dioxide, followed by Suzuki-Miyaura cross-coupling and Scholl-type cyclodehydrogenation. Due to the strained seven-membered ring and the inherent structural pattern, heteroatom-doped NGs 1-3 show C_s symmetrical, double saddle-helix hybrid conformation, which represents a new shape for HBC based nanographenes. The calculation studies reveal the low aromaticity of the 8π heterocycles themselves and the heterocycles also decrease the electron delocalization of benzenes surrounding them. Dynamics-based calculation suggests the C_s symmetry would maintain druing the saddle-inversion process. Meanwhile, we show property perturbation by doping with different heteroatoms.