Solid-state structures of peapod bearings composed of finite single-wall carbon nanotube and fullerene molecules

Confined Space Nanoarchitectonics for Dynamic Functions and Molecular Machines

Nanotechnology has advanced the techniques for elucidating phenomena at the atomic, molecular, and nano-level. As a post nanotechnology concept, nanoarchitectonics has emerged to create functional materials from unit structures. Consider the material function when nanoarchitectonics enables the design of materials whose internal structure is controlled at the nanometer level. Material function is determined by two elements. These are the functional unit that forms the core of the function and the environment (matrix) that surrounds it. This review paper discusses the nanoarchitectonics of confined space, which is a field for controlling functional materials and molecular machines. The first few sections introduce some of the various dynamic functions in confined spaces, considering molecular space, materials space, and biospace. In the latter two sections, examples of research on the behavior of molecular machines, such as molecular motors, in confined spaces are discussed. In particular, surface space and internal nanospace are taken up as typical examples of confined space. What these examples show is that not only the central functional unit, but also the surrounding spatial configuration is necessary for higher functional expression. Nanoarchitectonics will play important roles in the architecture of such a total system.

Recent advances in supramolecular fullerene chemistry

Fullerene chemistry has come a long way since 1990, when the first bulk production of C60 was reported. In the past decade, progress in supramolecular chemistry has opened some remarkable and previously unexpected opportunities regarding the selective (multiple) functionalization of fullerenes and their (self)assembly into larger structures and frameworks. The purpose of this review article is to provide a comprehensive overview of these recent developments. We describe how macrocycles and cages that bind strongly to C60 can be used to block undesired addition patterns and thus allow the selective preparation of single-isomer addition products. We also discuss how the emergence of highly shape-persistent macrocycles has opened opportunities for the study of photoactive fullerene dyads and triads as well as the preparation of mechanically interlocked compounds. The preparation of two- or three-dimensional fullerene materials is another research area that has seen remarkable progress over the past few years. Due to the rapidly decreasing price of C60 and C70, we believe that these achievements will translate into all fields where fullerenes have traditionally (third-generation solar cells) and more recently been applied (catalysis, spintronics).

Structures and Supramolecular Properties of Inclusion Complexes of Anthracene-Triptycene Nanocages with Fullerene Guests and Their Dynamic Motion as Molecular Gyroscopes

Three derivatives of macrocyclic cage compounds consisting of diarylanthracene and triptycene units were synthesized. These nanocages formed host-guest complexes with C₆₀ and other fullerene guests as confirmed by ¹ H NMR and fluorescence spectroscopy. The association constant of the mesityl and 2,4,6-tributoxyphenyl derivatives with C₆₀ was determined to be 2.2 × 10⁴  L mol^-1 , which was larger than that of the pentafluorophenyl derivative. Direct experimental evidence of the complexation was obtained by X-ray diffraction analysis: the guest C₆₀ molecule was included in the cavity via multipoint CH⋅⋅⋅π interactions. Dynamic disorders of the included C₆₀ molecule in variable-temperature X-ray analysis indicated uniaxial motion, such as gyroscopic motion. The unique dynamic behavior of the spherical C₆₀ rotor anchored by the cage stator via CH⋅⋅⋅π interactions in the crystal, as well as substituent effects on the association properties, are discussed with the aid of DFT calculations.

Synthesis of a Negatively Curved Nanocarbon Molecule with an Octagonal Omphalos via Design-of-Experiments Optimizations Supplemented by Machine Learning

A saddle-shaped nanocarbon molecule was synthesized, which revealed the existence of negative Gauss curvatures on a >3-nm molecular structure possessing 192 π-electrons. The synthesis was facilitated by a protocol developed with Design-of-Experiments optimizations and machine-learning predictions, and spectroscopy and crystallography were used to reveal the saddle-shaped structure of the molecule. Solution-phase analyses showed the presence of dimeric assembly, and crystallographic analyses revealed the stacked dimeric structures. The stacked crystal structure was scrutinized by various methods, including Gauss curvatures derived from the discrete surface theory of geometry, to reveal the important role of the molecular Gauss curvature in dimeric assembly.

Supramolecular Ensembles Formed via Calix[5]arene-Fullerene Host-Guest Interactions

This minireview introduces the research directions for the synthesis of supramolecular fullerene polymers. First, the discovery of host-guest complexes of pristine fullerenes is briefed. We focus on progress in supramolecular fullerene polymers directed by the use of calix[5]arene-fullerene interactions, which comprise linear, networked, helical arrays of fullerenes in supramolecular ensembles. The unique self-sorting behavior of right-handed and left-handed helical supramolecular fullerene arrays is discussed. Thereafter, an extensive investigation of the calix[5]arene-fullerene interaction for control over the chain structures of covalent polymers is introduced.

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.

A hybrid molecular peapod of sp2- and sp3-nanocarbons enabling ultrafast terahertz rotations

The internal hollow space of carbon nanotubes provides a unique nanometre-sized space to capture various molecular entities. The inner space circumfused by sp²-carbon networks can also encapsulate diamondoid molecules to afford sp²/sp³-hybrid nanocarbon peapods that have recently emerged as unique nanostructures. In this study, the sp²/sp³-hybrid peapods have been mimicked by adopting a cylindrical molecule and the smallest diamondoid, i.e., adamantane, to demonstrate the existence of ultrafast rotational motion. The solid-state rotational frequency is measured by NMR spectroscopy to record 1.06 THz that is, to the best of our knowledge, the largest value recorded for solid-state rotations of molecules. Theoretical calculations reveal that multivalent CH-π hydrogen bonds anchored the diamondoid guest on the π-wall of the cylindrical host. The weak hydrogen bonds are prone not only to cleave but also to regenerate at the interfaces, which give freedom to the guest for ultrafast isotropic rotations in the inertial regime.

Mechanical motions in hybrid sp²/sp³ -hybrid nanocarbon peapods might lead to promising materials applications, but have been insufficiently explored. Here the authors demonstrate that a diamondoid molecule trapped inside a carbonaceous cylinder undergoes solid-state rotations at terahertz frequencies.

Conjugated Nanohoops Incorporating Donor, Acceptor, Hetero- or Polycyclic Aromatics

In the last 13 years several synthetic strategies were developed that provide access to [n]cycloparaphenylenes ([n]CPPs) and related conjugated nanohoops. A number of potential applications emerged, including optoelectronic devices, and their use as templates for carbon nanomaterials and in supramolecular chemistry. To tune the structural or optoelectronic properties of carbon nanohoops beyond the size-dependent effect known for [n]CPPs, a variety of aromatic rings other than benzene were introduced. In this Review, we provide an overview of the syntheses, properties, and applications of conjugated nanohoops beyond [n]CPPs with intrinsic donor/acceptor structure or such that contain acceptor, donor, heteroaromatic or polycyclic aromatic units within the hoop as well as conjugated nanobelts.

Stereoselectivity in spontaneous assembly of rolled incommensurate carbon bilayers

The periodicity of two-dimensional entities can be manipulated by their stacking assembly, and incommensurate stacks of bilayers are attracting considerable interest in materials science. Stereoisomerism in incommensurate bilayers was first noted with incommensurate double-wall carbon nanotubes composed of helical carbon networks, but the lack of structural information hampered the chemical understanding such as the stereoselectivity during bilayer formation. In this study, we construct a finite molecular version of incommensurate carbon bilayers by assembling two helical cylindrical molecules in solution. An outer cylindrical molecule is designed to encapsulate a small-bore helical cylindrical molecule, and the spontaneous assembly of coaxial complexes proceeds in a stereoselective manner in solution with a preference for heterohelical combinations over diastereomeric, homohelical combinations. The rational design of incommensurate bilayers for material applications may be facilitated by the design and development of molecular versions with discrete structures with atomic precision.

Synthesis, Structures, and Properties of Highly Strained Cyclophenylene-Ethynylenes with Axial and Helical Chirality

Single and double cyclophenylene-ethynylenes (CPEs) with axial and helical chirality have been synthesized by the Sonogashira cross-coupling of di- and tetraethynyl biphenyls with a U-shaped prearomatic diiodoparaphenylene followed by reductive aromatization. X-ray crystallographic analyses and DFT calculations revealed that the CPEs possess highly twisted bent structures. Bend angles on the edge of the paraphenylene units were close to the value of [5]cycloparaphenylene (CPP)-the smallest CPP to date. The double and single CPEs possessed stable chirality despite flexible biphenyl structures because of the high strain in the diethynyl-paraphenylene moiety. In both the single and double CPEs, orbital interactions along the biphenyl axis were observed by DFT calculations in LUMO and LUMO+2 of the single CPE and LUMO+1 of the double CPE, which likely cause lowering of these orbital energies. Concerning chiroptical properties: boosting of the g_abs value was observed in the biphenyl-based double CPE, as well as the binaphthyl-based single CPE, compared to the biphenyl-based single CPE.

Theoretical study on aromatic and open-shell characteristics of carbon nanobelts composed of indeno[1,2-b]fluorene units: dependence on the number of units and charge states

In this study, we theoretically investigate the aromatic and open-shell characteristics of carbon nanobelts (CNBs) composed of five- and six-membered rings. We have designed nanobelts composed of indeno[1,2-b]fluorene ([1,2-b]IF) units, which are referred to as [N]IF-CNB (N: the number of five-membered rings). The number of π-electrons, n π, in neutral [N]IF-CNB is 7N, and thus depending on N and charge states, n π can be 4n + 2 and 4n. Quantum chemical calculations on neutral [6]IF-CNB and [8]IF-CNB and dicationic [8]IF-CNB2+ have revealed that they are expected to exhibit unique aromatic and open-shell characteristics depending on n π, there are several analogies of the electronic structures in [N]IF-CNB to those in [N]annulene. Delocalized and intermediate open-shell electronic structures of [N]IF-CNB are also useful to drastically change the third-order nonlinear optical properties. These results suggest that theoretically designed [N]IF-CNB can be attractive and challenging targets of organic synthesis for realizing novel open-shell functional conjugated macrocycles.

Enantioselective Synthesis of Planar Chiral Zigzag-Type Cyclophenylene Belts by Rhodium-Catalyzed Alkyne Cyclotrimerization

Planar chiral zigzag-type [8]- and [12]cyclophenylene (CP) belts have been synthesized in good yields with high ee values of 98% and 83%, respectively, by the rhodium-catalyzed enantioselective intramolecular sequential cyclotrimerizations of the corresponding cyclic polyynes. The observed high enantioselectivity arises from the regioselective formation of a rhodacycle intermediate from an unsymmetric triyne unit. The X-ray crystal structural analysis of the racemic planar chiral zigzag-type [8]CP belt revealed that the uneven molecules mesh with each other to form a one-dimensional columnar packing structure, in which one column contains single enantiomers, giving two types of chiral columns [(S)- and (R)-form columns] arranged alternately. The ring strain of the zigzag-type [8]CP belt was smaller than that of the armchair-type [8]CPP belt despite its smaller ring size, due to the presence of the strain-relieving m-terphenyl moieties. The effect of the number of the benzene rings of the zigzag-type CP belts on absorption and emission peaks was small due to interruption of π-conjugation at the m-phenylene moieties. However, the bending effect on the absolute fluorescence quantum yield as well as absorption and emission peaks was significant. Concerning chiroptical properties, the modest anisotropy dissymmetry factors of ECD and CPL were observed in the [8]CP belt.

The Supramolecular Chemistry of Cycloparaphenylenes and Their Analogs

Cycloparaphenylenes (CPPs) and their analogs have recently attracted much attention due to their aesthetical structures and optoelectronic properties with radial π-conjugation systems. The past 10 years have witnessed a remarkable advancement in CPPs research, from synthetic methodology to optoelectronic investigations. In this present minireview, we highlight the supramolecular chemistry of CPPs and their analogs, mainly focusing on the size-selective encapsulation of fullerenes, endohedral metallofullerenes, and small molecules by these hoop-shaped macrocycles. We will also discuss the assembly of molecular bearings using some belt-persistent tubular cycloarylene molecules and fullerenes, photoinduced electron transfer properties in supramolecular systems containing carbon nanohoop hosts and fullerene guests, as well as the shape recognition properties for structure self-sorting by using dumbbell-shaped dimer of [60]fullerene ligand. Besides, the supramolecular complexes with guest molecules other than fullerenes, such as CPPs themselves, iodine, pyridinium cations, and bowl-shaped corannulene, are also discussed.

The Supramolecular Chemistry of Strained Carbon Nanohoops

Since 1996, a growing number of strained macrocycles, comprising only sp² - or sp-hybridized carbon atoms within the ring, have become synthetically accessible, with the [n]cycloparaphenyleneacetylenes (CPPAs) and the [n]cycloparaphenylenes (CPPs) being the most prominent examples. Now that robust and relatively general synthetic routes toward a diverse range of nanohoop structures have become available, the research focus is beginning to shift towards the exploration of their properties and applications. From a supramolecular chemistry perspective, these macrocycles offer unique opportunities as a result of their near-perfect circular shape, the unusually high degree of shape-persistence, and the presence of both convex and concave π-faces. In this Minireview, we give an overview on the use of strained carbon-rich nanohoops in host-guest chemistry, the preparation of mechanically interlocked architectures, and crystal engineering.

Thermally activated isomeric all-hydrocarbon molecular receptors for fullerene separation

A new all-hydrocarbon macrocycle, cyclo[8](1,3-(4,6-dimethyl)benzene) (CDMB-8) has been reported. As prepared, it exists in Cs symmetry and shows no interaction with fullerenes (e.g., C60 or C70). High temperature (573 K) treatment induces thermal conversion of the material to an isomeric conformer with D4d symmetry as a receptor for fullerene separation.

Unbiased Rotational Motions of an Ellipsoidal Guest in a Tight Yet Pliable Host

In the design of machinery such as steel bearings, a fundamental understanding of material characteristics provides an indispensable basis for the design. Although hydrocarbon cycloarylenes have started to be used for providing unique supramolecular bearings with anomalous dynamic behaviors, their fundamental understanding is immature. A unique property of the cycloarylene host is now reported: the cyclic host is so pliable that it tracks the orientational changes of the ellipsoidal guest, that is, C₇₀ fullerene. Unique structures of the complex were revealed by spectroscopic and crystallographic analyses, and additional theoretical investigations deepened our understanding by revealing the structural changes associated with unbiased rotational motions.

Concyclic CH-π arrays for single-axis rotations of a bowl in a tube

The hydrogen bond is undoubtedly one of the most important non-covalent interactions. Among the several types of the hydrogen bonds, the CH-π interaction is a relatively new notion that is being recognised in chemistry and biology. Although the CH-π hydrogen bond and conventional hydrogen bonds share common features such as directionality, this weak interaction has played a secondary role in molecular recognition. In this study, we have devised a host-guest complex that is assembled solely by the CH-π hydrogen bonds. Multivalent interactions of a bowl-shaped hydrocarbon with its peripheral hydrogen atoms are made possible via CH-π hydrogen bonds by adopting a tubular hydrocarbon as a host for their enthalpy-driven complexation. Concyclic arrays of weak hydrogen bonds further allow dynamic rotational motions of the guest in the host. Solid-state analysis with crystallographic and spectroscopic methods reveal a single-axis rotation of the bowl in the tube.

Ratchet-free solid-state inertial rotation of a guest ball in a tight tubular host

Dynamics of molecules in the solid state holds promise for connecting molecular behaviors with properties of bulk materials. Solid-state dynamics of [60]fullerene (C₆₀) is controlled by intimate intermolecular contacts and results in restricted motions of a ratchet phase at low temperatures. Manipulation of the solid-state dynamics of fullerene molecules is thus an interesting yet challenging problem. Here we show that a tubular host for C₆₀ liberates the solid-state dynamics of the guest from the motional restrictions. Although the intermolecular contacts between the host and C₆₀ were present to enable a tight association with a large energy gain of –14 kcal mol^–1, the dynamic rotations of C₆₀ were simultaneously enabled by a small energy barrier of +2 kcal mol^–1 for the reorientation. The solid-state rotational motions reached a non-Brownian, inertial regime with an extremely rapid rotational frequency of 213 GHz at 335 K.

Though dynamics of molecules are generally restricted by intermolecular contacts, C₆₀ fullerene is able to rotate freely despite being tightly bound inside a molecular host. Here, the authors study the solid-state dynamics of this host-guest system to understand the anomalous relationship between tight association and low friction.

Polyaromatic molecular tubes: from strategic synthesis to host functions

Ring- and tube-shaped molecules like crown ethers and cyclodextrins play a fundamental role in supramolecular chemistry since their initial discovery. To date, numerous intriguing properties and reactivities have been reported based on their unique inner microenvironments. While inner spaces encircled by aliphatic and/or small aromatic frameworks have been heavily investigated, tubular structures that feature polyaromatic frameworks remained largely unexplored until 2010, despite their undisputable potential. Polyaromatic rings provide appealing photophysical and electrochemical properties and thus allow for the construction of new functional cylindrical nanospaces. This feature article describes the recent progress in the synthesis and application of short tubular molecules bearing multiple (≥3) polyaromatic rings (e.g., anthracene, pyrene, chrysene, and HBC). The polyaromatic tubes reported herein display characteristic properties such as strong fluorescent emission, a selective molecular binding ability, efficient host-guest energy transfer and open-closed structural transformations.

A Saturn-Like Complex Composed of Macrocyclic Oligothiophene and C60 Fullerene: Structure, Stability, and Photophysical Properties in Solution and the Solid State

A Saturn-like 1:1 complex composed of macrocyclic oligothiophene E-8T7A and C₆₀ fullerene (C₆₀ ) was synthesized to investigate the interaction between macrocyclic oligothiophenes and C₆₀ in solution and the solid state. Because the Saturn-like 1:1 complex E-8T7A⋅C₆₀ is mainly stabilized by van der Waals interactions between C₆₀ and the sulfur atoms of the E-8T7A macrocycle, C₆₀ is rather weakly incorporated inside the macro-ring in solution. However, in the solid state the Saturn-like 1:1 complex preferentially formed single crystals or nanostructured polymorphs. Interestingly, X-ray analysis and theoretical calculations exhibited hindered rotation of C₆₀ in the Saturn-like complex due to interactions between C₆₀ and the sulfur atoms. Furthermore, the photoinduced charge transfer (CT) interaction between E-8T7A and C₆₀ in solution was investigated by using femtosecond transient absorption (TA) spectroscopy. The ultrafast TA spectral changes in the photoinduced absorption bands were attributed to the CT process in the Saturn-like structure.

Chiral intertwined spirals and magnetic transition dipole moments dictated by cylinder helicity

The presence of anomalous chirality in a roll of graphitic carbon sheets has been recognized since the discovery of carbon nanotubes, which are becoming available in higher quantities through the isolation of chiral single-wall congeners with high purity. Exploration of the properties arising from cylinder chirality is expected to expand the scope of tubular entities in the future. By studying molecular fragments of helical carbon nanotubes, we herein reveal interesting properties that arise from this chirality. The chirality of nanoscale cylinders resulted in chirality of larger dimensions in the form of a double-helix assembly. Cylinder chirality in solution gave rise to a large dissymmetry factor of metal-free entities in circular polarized luminescence. Theoretical investigations revealed the pivotal role of cylindrical shapes in enhancing magnetic dipole transition moments to yield extreme rotatory strength. Unique effects of cylinder chirality in this study may prompt the development of tubular entities, for instance, toward chiroptical applications.

Assembly, Thermodynamics, and Structure of a Two-Wheeled Composite of a Dumbbell-Shaped Molecule and Cylindrical Molecules with Different Edges

A carbonaceous dumbbell was able to spontaneously glue two tubular receptors to form a unique two-wheeled composite through van der Waals interactions, thus forcing the wheel components into contact with each other at the edges. In the present study, two tubular receptors with enantiomeric carbon networks were assembled on the dumbbell joint, and the handedness of the receptors was discriminated, thus leading to the self-sorting of homomeric receptors from a mixture of enantiomeric tubes. The crystal structures of the composites revealed the structural origins of the molecular recognition driven by van der Waals forces as well as the presence of a columnar array of C₁₂₀ molecules in a 1:1 composite.

Shortest Double-Walled Carbon Nanotubes Composed of Cycloparaphenylenes

The host-guest chemistry of cycloparaphenylenes (CPPs) of different sizes is described. [n]CPPs (n=5, 6, 7, 8, and 10) selectively interact with [n+5]CPPs, forming complexes [n+5]CPP⊃[n]CPP, which are the shortest double-walled armchair carbon nanotubes. The size selectivity is dictated by the difference in diameters of the CPPs (that is, 0.34-0.35 nm), which maximizes attractive van der Waals interactions. Theoretical calculations suggest that the orbital energies of the CPPs become perturbed upon complex formation, and orbital mixing between the two CPPs is predicted for large CPP pairs. The association constants in 1,1,2,2-[D₂ ]tetrachloroethane, estimated by ¹ H NMR titration, are approximately 10³  mol L^-1 at 50 °C. Van't Hoff plot analysis reveals that complexation is driven mainly by entropy owing to desolvation of the CPPs. [13]CPP also forms a complex with [4]cyclo-2,7-pyrenylene ([4]CPY), which is a π-extended [8]CPP. Theoretical calculations suggest that the formation of [13]CPP⊃[4]CPY is more exothermic than that of [13]CPP⊃[8]CPP. A ternary complex, [15]CPP⊃[10]CPP⊃C₆₀ , is also formed by mixing [15]CPP and [10]CPP⊃C₆₀ .

Buckyball sandwiches

Two-dimensional (2D) materials have considerably expanded the field of materials science in the past decade. Even more recently, various 2D materials have been assembled into vertical van der Waals heterostacks, and it has been proposed to combine them with other low-dimensional structures to create new materials with hybridized properties. We demonstrate the first direct images of a suspended 0D/2D heterostructure that incorporates C₆₀ molecules between two graphene layers in a buckyball sandwich structure. We find clean and ordered C₆₀ islands with thicknesses down to one molecule, shielded by the graphene layers from the microscope vacuum and partially protected from radiation damage during scanning transmission electron microscopy imaging. The sandwich structure serves as a 2D nanoscale reaction chamber, allowing the analysis of the structure of the molecules and their dynamics at atomic resolution.

Structures and properties of Saturn-like complexes composed of oligothiophene macrocycle with methano[60]fullerene and [70]fullerene

π-Expanded oligothienylene macrocycle with a large inner cavity incorporates fullerenes such as methano[60]fullerene (C61H2) and [70]fullerene (C70) inside to form Saturn-like complexes. Although the oligothiophene macrocycle weakly interacts with fullerenes in solution, it forms stable Saturn-like fullerene complexes in the solid state. X-ray analysis of the Saturn-like complexes exhibited short contacts between the sulfur atoms of the oligothiophene macrocycle and fullerene carbons, which hinder the rotation of fullerenes. As a result, the non-covalent interaction between the oligothiophene macrocycle and fullerenes was employed in crystal structure determination of fullerenes. UV–vis–NIR spectra of the Saturn-like complexes showed weak donor–acceptor interaction between the oligothiophene macrocycle and fullerenes.

An Operationally Simple and Mild Oxidative Homocoupling of Aryl Boronic Esters To Access Conformationally Constrained Macrocycles

Constrained macrocyclic scaffolds are recognized as challenging synthetic motifs with few general macrocyclization methods capable of accessing these types of systems. Although palladium catalyzed oxidative homocoupling of aryl boronic acids and esters to biphenyls has been recognized as a common byproduct in Suzuki-Miyaura cross-couplings for decades, this reactivity has not been leveraged for the synthesis of challenging molecules. Here we report an oxidative boronic ester homocoupling reaction as a mild method for the synthesis of strained and conformationally restricted macrocycles. Higher yields and better efficiencies are observed for intramolecular diboronic ester homocouplings when directly compared to the analogous intramolecular Suzuki-Miyaura cross-couplings or reductive Yamamoto homocouplings. Substrates included strained polyphenylene macrocycles, strained cycloalkynes, and a key macrocyclic intermediate toward the synthesis of acerogenin A. Notably, this oxidative homocoupling reaction is performed at room temperature, open to atmosphere, and without the need to rigorously exclude water, thus representing an operationally simple alternative to traditional cross-coupling macrocyclizations. The mechanism of the reaction was investigated indicating that 1-5 nm palladium nanoparticles may serve as the active catalyst.

Chemical Synthesis of Cycloparaphenylenes

Cycloparaphenylenes and analogues thereof are substances having excellent structural and electronic properties due to radial π-conjugation modes and porous structures. Since they are partial structures of carbon nanotubes, they have also attracted attention as a template for carbon nanotube synthesis. In this chapter, we introduce a series of research on the synthesis of cycloparaphenylenes and their analogues.

Solid-State Emission of the Anthracene-o-Carborane Dyad from the Twisted-Intramolecular Charge Transfer in the Crystalline State

The emission process of the o-carborane dyad with anthracene originating from the twisted intramolecular charge transfer (TICT) state in the crystalline state is described. The anthracene-o-carborane dyad was synthesized and its optical properties were investigated. Initially, the dyad had aggregation- and crystallization-induced emission enhancement (AIEE and CIEE) properties via the intramolecular charge transfer (ICT) state. Interestingly, the dyad presented the dual-emissions assigned to both locally excited (LE) and ICT states in solution. From the mechanistic studies and computer calculations, it was indicated that the emission band from the ICT should be attributable to the TICT emission. Surprisingly, even in the crystalline state, the TICT emission was observed. It was proposed from that the compact sphere shape of o-carborane would allow for rotation even in the condensed state.