Oxygen‐ and Nitrogen‐Embedded Zigzag Hydrocarbon Belts

Synthesis and properties of an O-doped aromatic belt

A new macrocyclic arene, dibenzofuran[3]arene, was synthesized, which could be conveniently transformed to an O-doped aromatic belt with a rigid ring-shaped structure and deep cavity. Moreover, the O-doped aromatic belt also showed a high HOMO energy and a narrow HOMO-LUMO gap experimentally and theoretically.

A step towards rational design of carbon nanobelts with tunable electronic properties

Belt-shaped aromatic compounds are among the most attractive classes of radial π-conjugated nanocarbon molecules with unique physical and chemical properties. In this work, we computationally studied a number of all-carbon and heteroatom-bridged nanobelts, as well as their inclusion complexes with fullerene C60. Our results provide a useful guide for modulating the electronic properties of the nanobelts. An in-depth analysis of the ground and excited state properties of their complexes has allowed us to establish structure-property relationships and propose simple principles for the design of nanobelts with improved electron-donating properties suitable for photovoltaic applications.

Recent advances in the synthesis and applications of macrocyclic arenes

Macrocyclic arenes including calixarenes, resorcinarenes, cyclotriveratrylene, pillararenes and so on have emerged as highly attractive synthetic macrocyclic hosts due to their unique structures, facile functionalization, and broad range of applications. In recent years, there has been growing interest in the development of novel macrocyclic arenes composed of various aromatic building blocks bridged by methylene groups, which have found applications in various research areas. Consequently, the development of novel macrocyclic arenes has become a frontier and hot topic in supramolecular and macrocyclic chemistry. In this review, we feature the recent advances in the synthesis and applications of novel macrocyclic arenes that have emerged in the last decade. The general synthetic strategies employed for these macrocyclic arenes are systematically summarized, and their wide applications in molecular recognition and assemblies, molecular machines, biomedical science and functional materials are highlighted.

Electrostatic Potential for Exploring Electron Delocalization in Infinitenes, Circulenes, and Nanobelts

The π-conjugation, aromaticity, and stability of the newly synthesized 12-infinitene and of other infinitenes comprising 8-, 10-, 14-, and 16-arene rings are investigated using density functional theory. The π-electron delocalization and aromatic character rooted in infinitenes are quantified in terms of molecular electrostatic potential (MESP) topology. Structurally, the infinitene bears a close resemblance of its helically twisted structure to the infinity symbol. The MESP topology shows that infinitene possesses an infinity-shaped delocalization of the electron density that streams over the fused benzenoid rings. The parameter ∑i=13Δλi, derived from the eigenvalues (λ_i) corresponding to the MESP minima, is used for quantifying the aromatic character of arene rings of infinitene. The structure, stability, and MESP topology features of 8-, 10-, 12-, 14-, and 16-infinitenes are also compared with the corresponding isomeric circulenes and carbon nanobelts. Further, the strain in all such systems is evaluated by considering the respective isomeric planar benzenoid hydrocarbons as reference systems. The 12-infinitene turns out to be the most aromatic and the least strained among all the systems examined.

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.

Macrocyclic host molecules with aromatic building blocks: the state of the art and progress

Macrocyclic host molecules play the central role in host-guest chemistry and supramolecular chemistry. The highly structural symmetry of macrocyclic host molecules can meet people's pursuit of aesthetics in molecular design, and generally means a balance of design, synthesis, properties and applications. For macrocyclic host molecules with highly symmetrical structures, building blocks, which could be described as repeat units as well, are the most fundamental elements for molecular design. The structural features and recognition ability of macrocyclic host molecules are determined by the building blocks and their connection patterns. Using different building blocks, different macrocyclic host molecules could be designed and synthesized. With decades of developments of host-guest chemistry and supramolecular chemistry, diverse macrocyclic host molecules with different building blocks have been designed and synthesized. Aromatic building blocks are a big family among the various building blocks used in constructing macrocyclic host molecules. In this feature article, the recent developments of macrocyclic host molecules with aromatic building blocks were summarized and discussed.

Xanthene[n]arenes: Exceptionally Large, Bowl-Shaped Macrocyclic Building Blocks Suitable for Self-Assembly

A new class of macrocycles denoted as "xanthene[n]arenes" was synthesized. In contrast to most other macrocycles, they feature a conformationally restricted bowl shape due to the attached alkyl groups at the linking methylene units. This facilitates the synthesis of cavitands and the self-assembly to molecular capsules via noncovalent interactions. The derivatization potential of the novel macrocycles was demonstrated on the xanthene[3]arene scaffold. Besides a deep cavitand and an oxygen-embedded zigzag hydrocarbon belt[12]arene, a modified macrocycle was synthesized that self-assembles into a hydrogen-bonded tetrameric capsule, demonstrating the potential of xanthene[n]arenes as a new set of macrocyclic building blocks.

Synthesis and Physical Properties of a Phenanthrene-Based [6,6] Hollow Bilayer Cylindrical Nanoring

Herein, we report the synthesis and properties of a [6,6] hollow bilayer cylindrical nanoring (HBCNR) from a planar macrocycle via a Diels-Alder and Yamamoto coupling reaction. The fluorescence quantum yield of HBCNR was determined to be Φ_F = 52%, which is four times higher than its precursor. In addition, its hollow nanoring configuration was also simulated by theoretical studies, and the tension energy was estimated to be 47.1 kcal/mol.

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.

Sulphur-Embedded Hydrocarbon Belts: Synthesis, Structure and Redox Chemistry of Cyclothianthrenes

Cyclothianthrenes, a series of sulphur-embedded hydrocarbon belts proposed a decade ago, were successfully constructed through a stepwise bottom-up synthesis. The belt [6]cyclothianthrene ([6]CT) is the smallest and most strained member of the family yet reported. Both [6]CT and [8]CT are the first examples of cyclothianthrene characterized by single crystal X-ray diffraction. An unprecedented chiral belt [7]CT and a Möbius-shaped [9]CT were also achieved via modular synthesis. Crystallographic and computational studies show that belts [6]CT-[8]CT have prism-like conformations with well-defined tubular cavities which have potential for guest molecule inclusion. Cyclic voltammograms further revealed that these belts are redox-active. The success of constructing sulphur-embedded hydrocarbon belts, that is, cyclothianthrenes, greatly enriches the chemistry of heteroatom-doped molecular belts and tubes.

A Green Fluorescent Nitrogen-Doped Aromatic Belt Containing a [6]Cycloparaphenylene Skeleton

The design and synthesis of nitrogen-doped aromatic belts with conjugated structures still remain a challenge. Here, we report the first nitrogen-doped aromatic belt with a [6]cycloparaphenylene skeleton, which is conveniently synthesized from the easily available calix[3]carbazole. The aromatic belt has a rigid conjugated structure and deep cavity, and it can encapsulate one dichloromethane both in solution and in the solid state. Interestingly, the aromatic belt shows strong green fluorescence with a quantum yield of 0.39 and exhibits a narrow HOMO-LUMO energy gap of 2.02 eV. The belt-shaped conjugated structure composed of three carbazole subunits has specific optoelectronic properties that will promote wide applications in supramolecular chemistry and materials science.