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Electronic and vibrational relaxation processes can be optimized and tuned by introducing alternative pathways that channel excess energy more efficiently. An ensemble of interacting molecular systems can help overcome the bottlenecks caused by large energy gaps between intermediate excited states involved in the relaxation process. By employing this strategy, catenanes composed of mechanically interlocked carbon nanostructures show great promise as new materials for achieving higher efficiencies in electronic devices. Herein, we perform nonadiabatic excited state molecular dynamics on different all‐benzene catenanes. We observe that catenanes experience faster relaxations than individual units. Coupled catenanes present overlapping energy manifolds that include several electronic excited states spatially localized on the different moieties, increasing the density of states that ultimately improve the efficiency in the energy relaxation. This result suggests the use of catenanes as a viable strategy for tuning the internal conversion rates in a quest for their utilization for new optoelectronic applications. [ABSTRACT FROM AUTHOR]

Molecules with a π-system that can be mapped onto a Möbius strip may display Möbius aromaticity. Such molecules are difficult to synthesize because they have a twisted structure. Recently, we combined chiral [6]helicene and fluorescent [7]cycloparaphenylene, and synthesized the first helicene para -phenylene ([6,7]HPP) carbon nanohoop. We have demonstrated that this design strategy ultimately provides a Möbius topology of the molecular π-electron system and, therefore, offers the potential to study Möbius aromaticity experimentally. In addition, the synthesized nanohoop exists as a mixture of conformers in solution. Some of the conformers possess a different orientability of their π-systems, i.e., they differ in their topology. As a result, the recorded circularly polarized luminescence of isolated enantiomers displays both left- and right-handedness of the emitted light, each emanating from a conformer with a different π-system topology. Therefore, [6,7]HPP provided the first experimental evidence of such topological bistability in carbon nanohoops. [ABSTRACT FROM AUTHOR]

Herein, we report the synthesis of a novel intramolecular donor‐acceptor (D−A) system ([12]CPP‐8TPAOMe) based on cycloparaphenylenes (CPPs) grafted with eight di(4‐methoxyphenyl)amino groups (TPAOMe) as donors. Compared to [12]CPP, D−A nanohoop exhibited significant changes in physical properties, including a large redshift (>78 nm) in the fluorescence spectrum and novel positive solvatofluorochromic properties with a maximum peak ranging from 484 nm to 546 nm. The potential applications of [12]CPP‐8TPAOMe in electron‐ and hole‐transport devices were further investigated, and its bipolar behavior as a charge transport active layer was clearly observed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

"Improbable" rotaxanes consisting of interlocked conjugated components represent non‐trivial synthetic targets, not to mention those with all‐benzene scaffolds. Herein, a modular synthetic strategy has been established using an isolable azo‐linked pre‐rotaxane as the core module, in which the azo group functions as a tracelessly removable template to direct mechanical bond formations. Through versatile connections of the pre‐rotaxane and other customizable modules, [2]‐ and [3]rotaxanes derived from all‐benzene scaffolds have been accomplished, demonstrating the utility and potential of the synthetic design for all‐benzene interlocked supramolecules. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The synthesis of a new nanohoop containing a stereogenic Tröger's base skeleton tethered to a curved hexaparaphenylene ([6]CPP) is reported. The TB[6]CPP nanohoop possesses a stable C2 symmetrical structure, which promotes the allowed transition that gives rise to pale blue emission with a quantum yield of ~0.69, surpassing the value of the more symmetrical [8]CPP. Moreover, TB[6]CPP shows chiroptical properties including circular dichroism and circularly polarized luminescence with a moderate dissymmetry factor (|glum|) of ~2.1×10−3 [ABSTRACT FROM AUTHOR]

Carbon nanorings are macrocyclic aromatic hydrocarbons that represent the segments of carbon nanotubes and have received considerable attention due to their novel nanoelectronic and photophysical capabilities. The cycloparaphenylene (CPP), a carbon nanoring with a ring-like structure comprising of only benzene units, has been the subject matter of several studies. The carbon nanoring structures bearing polycyclic aromatic hydrocarbons such as hexabenzocoronene and pyrene molecules are also found to exhibit exciting characteristics and applications. This in turn evolves a wide range of novel chemical structures whose behavior and attributes are to be studied and explored. Molecular descriptors help us to study such novel nanostructures by providing a greater understanding of their unique properties, whereas such characterization remains challenging due to their ring-shaped arrangement. In this study, we investigate cycloparaphenylene series and show that such structures are not bounded by the partial cube family. We also derive the exact analytic expressions of degree, distance and closeness-related descriptors. We have also computed the thermodynamic and kinetic stabilities of the three structures using the graph spectra, resonance energies, HOMO-LUMO gaps and Kekulé counts obtained from the graph spectra and combinatorial methods. Whereas the CPPhbc[5] structure is thermodynamically more stable, the CPPyr[9] is kinetically more stable. Furthermore, we have employed combinatorial generating function methods to compute the NMR and ESR spectra of the title compounds. [ABSTRACT FROM AUTHOR]

Keywords: cycloparaphenylenes; cyclonaphthylenes; molecular nanocarbons; carbon nanobelts; methylene-bridged nanobelts; prism[6]arenes EN cycloparaphenylenes cyclonaphthylenes molecular nanocarbons carbon nanobelts methylene-bridged nanobelts prism[6]arenes 1433 1436 4 07/11/23 20230725 NES 230725 Graph Aromatic nanobelts are molecules that have attracted a great deal of attention in recent chemistry. [6]MCN was extracted from the reaction mixture by using a large amount of toluene, in which [6]MCN is slightly soluble, affording pure [6]MCN after two cycles of precipitation with 1:2 toluene-hexane. 2014, 50: 5774 24 Li, Y. Segawa, Y. Yagi, A. Itami, K. J. Am. Chem. Soc. 2020, 142: 12850 25 Yagi, A. Segawa, Y. Itami, K. J. Am. Chem. Soc. 2012, 134: 2962 26 Sun, Z. Sarkar, P. Suenaga, T. Sato, S. Isobe, H. Angew. Int. Ed. 2015, 54: 12800 27 Okada, K. Yagi, A. Segawa, Y. Itami, K. Chem. Sci. 2017, 8: 661 28 Jia, H. Gao, Y. Huang, Q. Cui, S. Du, P. Chem. Commun. [Extracted from the article]

We report the synthesis and characterization of a novel type of nanohoop, consisting of a cycloparaphenylene derivative incorporating a curved heptagon‐containing π‐extended polycyclic aromatic hydrocarbon (PAH) unit. We demonstrate that this new macrocycle behaves as a supramolecular receptor of curved π‐systems such as fullerenes C60 and C70, with remarkably large binding constants (ca. 107 M−1), as estimated by fluorescence measurements. Nanosecond and femtosecond spectroscopic analysis show that these host‐guest complexes are capable of quasi‐instantaneous charge separation upon photoexcitation, due to the ultrafast charge transfer from the macrocycle to the complexed fullerene. These results demonstrate saddle‐shaped PAHs with dibenzocycloheptatrienone motifs as structural components for new macrocycles displaying molecular receptor abilities and versatile photochemical responses with promising electron‐donor properties in host‐guest complexes. [ABSTRACT FROM AUTHOR]

The synthesis of topological molecular nanocarbons, such as hoop-like [ n ]cycloparaphenylenes, requires the use of spatially prearranged, pro-aromatic units to overcome a build-up of large molecular strain in their curved structures. The used cyclohexadienyl units, however, contain tertiary alcohols that need protection to prevent side reactions until the aromatization step that affords the final curved hydrocarbon. Although alkyl and triethylsilyl groups have been successfully applied as protecting groups for this purpose, each suffers from specific drawbacks. Here, we explore the potential of sterically more crowded silyl groups, namely, tert -butyldimethylsilyl and triisopropylsilyl, as alternatives to the established protection strategies. We show that tert -butyldimethylsilyl can be easily installed and removed under mild conditions, displaying markedly higher resistance towards acids or bases than the triethylsilyl group used to date. Unlike in the case of alkyl groups, tert -butyldimethylsilyl also preserves a high stereoselectivity during the nucleophilic additions of ArLi. Furthermore, we demonstrate that both tert -butyldimethylsilyl and triethylsilyl groups can be installed on the same substrate, and that the latter be selectively deprotected. Thus, the high stereoselectivity, improved stability, and easy deprotection make tert -butyldimethylsilyl an excellent protecting group for the synthesis of carbon nanohoops. [ABSTRACT FROM AUTHOR]

An ethylene glycol‐decorated [6]cyclo‐meta‐phenylene (CMP) macrocycle was synthesized and utilized as a subunit to construct a fourfold AuI2−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. [ABSTRACT FROM AUTHOR]

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 ⊃C60/70)+ ⋅/- ⋅ 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. [ABSTRACT FROM AUTHOR]

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 ⊃C60/70)+ ⋅/- ⋅ 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. [ABSTRACT FROM AUTHOR]

The combination of carbon‐based nanohoops with other functional organic molecular structures should lead to the design of new molecular configurations with interesting properties. Here, necklace‐like nanohoops embedded with carborane were synthesized for the first time. The unique deboronization of o‐carborane has led to the facile preparation of ionic nanohoop compounds. Nanohoops functionalized by nido‐o‐carborane show excellent fluorescence emission, with a solution quantum yield of up to 90.0 % in THF and a solid‐state quantum efficiency of 87.3 %, which opens an avenue for the applications of the nanohoops in OLEDs and bioimaging. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Polycyclic aromatic hydrocarbons (PAHs) are promising nanocarbon materials with diverse optoelectronic properties, yet they also pose concerning environmental and health risks. Despite the ubiquity of PAHs in the environment (crude oil, emissions, and biomass), most supermolecules rely on heteroatoms for stability. We discovered and characterized a family of all-hydrocarbon, all-π-conjugated [n]cycloparaphenylene-PAH host-guest complexes. We built a theoretical framework to rapidly select these complexes and predict their stabilities, driven exclusively by CH−π interactions. More than a dozen complexes were confirmed experimentally and assembled directly from commercially available compounds. This motif offers a versatile way to combine the advantageous properties of organic semiconductors with the rich dynamic, stereochemical, stimulus-responsive, and stress-dissipative behavior of host-guest complexes, while creating new opportunities for bespoke PAH separation or remediation materials. [ABSTRACT FROM AUTHOR]

Conjugated nanohoops are excellent as candidates for studying structure–property relationships, as optoelectronic materials, and as hosts for supramolecular chemistry. Whereas carbon nanohoops containing aromatics have been well studied, antiaromatic units had not been incorporated until our group recently did so, using dibenzo[ a , e ]pentalene (DBP). The nonalternant electronic character of the DBP units significantly influences the optoelectronic properties of such nanohoops. Here, we summarize our synthetic strategies toward DBP-containing nanohoops, together with their structural and electronic properties, chirality, and host–guest chemistry. We demonstrate how incorporating antiaromatic units leads to unique properties and opens new synthetic avenues, making such nanohoops attractive as potential electronic materials. 1 Introduction 2 Synthesis 3 Structural Properties 4 Electronic Properties 5 Chirality 6 Host–Guest Chemistry [ABSTRACT FROM AUTHOR]

Abstract The preparation of cycloparaphenylenes ([n]CPPs) with their bent π-system poses a long-standing challenge in organic synthesis. In the current multi-step approaches to access CPPs, pre-angulated precursors were combined using transition metal-catalysed or mediated coupling reactions. Therefore, there is a long way to the realisation of the idea of an ‘ideal synthesis’. An easy and efficient synthesis of different [n]CPPs would represent a breakthrough, also pushing their incorporation into organic materials. By combining multiple steps in a one-pot approach, the overall time and workload can be drastically shortened. Herein, we present the application of this concept for the preparation of [6] and [9]CPP as a simple and fast alternative to current methods. By tuning the reaction conditions the selective synthesis of both [6] and [9]CPP was demonstrated.

Structural designs combining cycloparaphenylenes (CPPs) backbone with planar chiral [2.2]paracyclophane ([2.2]PCP) lead to optical‐active chiral macrocycles with intriguing properties. X‐ray crystal analysis revealed aesthetic necklace‐shaped structures and size‐dependent packages with long‐range channels. The macrocycles exhibit unique photophysical properties with high fluorescence quantum yield of up to 82 %, and the fluorescent color varies with ring size. In addition, size‐dependent chiroptical properties with moderately large CPL dissymmetry factor of 10−3 and CPL brightness in the range of 30–40 M−1 cm−1 were observed. [ABSTRACT FROM AUTHOR]

Strained aromatic macrocycles based on cycloparaphenylenes (CPPs) are the shortest repeating units of armchair single-walled carbon nanotubes. Since the development of several new synthetic methodologies for accessing these structures, their properties have been extensively studied. Besides the fundamental interest in these novel molecular scaffolds, their application in the field of materials science is an ongoing topic of research. Most of the reported CPP-type macrocycles display strong binding toward fullerenes, due to the perfect match between the convex and concave π-surfaces of fullerenes and CPPs, respectively. Highly functionalized CPP derivatives capable of supramolecular binding with other molecules are rarely reported. The synthesis of highly functionalized [ n ]cyclo-2,7-pyrenylenes leads to CPP-type macrocycles with a defined cavity capable of binding non-fullerene guests with high association constants. [ABSTRACT FROM AUTHOR]

The synthesis, structures, and properties of [4]cyclonaphthodithiophene diimides ([4]C‐NDTIs) are described. NDTIs as important n‐type building blocks were catenated in the α‐positions of thiophene rings via an unusual electrochemical‐oxidation‐promoted macrocyclization route. The thiophene–thiophene junction in [4]C‐NDTIs results in an ideal pillar shape. This interesting topology, along with appealing electronic and optical properties inherited from the NDTI units, endows the [4]C‐NDTIs with both near‐infrared (NIR) light absorptions, strong excitonic coupling, and tight encapsulation of C60. Stable orientations of the NDTI units in the nanopillars lead to stable inherent chirality, which enables detailed circular dichroism studies on the impact of isomeric structures on π‐conjugation. Remarkably, the [4]C‐NDTIs maintain the strong π–π stacking abilities of NDTI units and thus adopt two‐dimensional (2D) lattice arrays at the molecular level. These nanopillar molecules have great potential to mimic natural photosynthetic systems for the development of multifunctional organic materials. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A set of strained aromatic macrocycles based on [n]cyclo‐2,7‐(4,5,9,10‐tetrahydro)pyrenylenes is presented with size‐dependent photophysical properties. The K‐region of pyrene was functionalized with ethylene glycol groups to decorate the outer rim and thereby confine the space inside the macrocycle. This confined space is especially pronounced for n=5, which leads to an internal binding of up to 8.0×104 m−1 between the ether‐decorated [5]cyclo‐2,7‐pyrenylene and shape‐complementary crown ether–cation complexes. Both the ether‐decorated [n]cyclo‐pyrenylenes as well as one of their host–guest complexes have been structurally characterized by single‐crystal X‐ray analysis. In combination with computational methods the structural and thermodynamic reasons for the exceptionally strong binding have been elucidated. The presented rim confinement strategy makes cycloparaphenylenes an attractive supramolecular host family with a favorable, size‐independent read‐out signature and binding capabilities extending beyond fullerene guests. [ABSTRACT FROM AUTHOR]

A number of non‐covalently bound donor‐acceptor dyads, consisting of C60 as the electron acceptor and cycloparaphenylene (CPP) as the electron donor, have been reported. A hypsochromic shift of the charge transfer (CT) band in polar medium has been found in [10]CPP⊃Li+@C60. To explore this anomalous effect, we study inclusion complexes [10]CPP⊃Li+@C60‐MP, [10]CPP⊃C60‐MPH+, and [10]CPP⊃C60‐PPyMe+ formed by fulleropyrrolidine derivatives and [10]CPP using the DFT/TDDFT approach. We show that the introduction of a positively charged fragment into fullerene stabilizes CT states that become the lowest‐lying excited states. These charge‐separated states can be generated by the decay of locally excited states on a nanosecond to picosecond time scale. The distance of the charged fragment to the center of the fullerenic cage and its accessibility to the solvent determine the strength of the hypsochromic shift. [ABSTRACT FROM AUTHOR]

Conjugated nanohoops allow to investigate the effect of radial conjugation and bending on the involved π‐systems. They can possess unexpected optoelectronic properties and their radially oriented π‐system makes them attractive for host–guest chemistry. Bending the π‐subsystems can lead to chiral hoops. Herein, we report the stereoselective synthesis of two enantiomers of chiral conjugated nanohoops by incorporating dibenzo[a,e]pentalenes (DBPs), which are generated in the last synthetic step from enantiomerically pure diketone precursors. Owing to its bent shape, this diketone unit was used as the only bent precursor and novel "corner unit" in the synthesis of the hoops. The [6]DBP[4]Ph‐hoops contain six antiaromatic DBP units and four bridging phenylene groups. The small HOMO–LUMO gap and ambipolar electrochemical character of the DBP units is reflected in the optoelectronic properties of the hoop. Electronic circular dichroism spectra and MD simulations showed that the chiral hoop did not racemize even when heated to 110 °C. Due to its large diameter, it was able to accommodate two C60 molecules, as binding studies indicate. [ABSTRACT FROM AUTHOR]

The synthesis of new carbon nanoforms with remarkable and fine‐tuned bulk properties still represents a formidable challenge, with cyclic organic nanorings emerging in recent years for the template‐driven design of this kind of systems. The design and engineering of these materials can be first controlled at the molecular scale, to further induce their specific self‐assembly toward tailored properties at the nanoscale. Theoretical studies have lately contributed to the understanding of the underlying physical effects, the development of synthetic strategies, and the rationalization of novel materials properties, employing a variety of methods ranging from accurate calculations of isolated molecules to atomistic molecular dynamics simulations of a large sample of molecules in realistic conditions, which will be reviewed here with a focus on the transition from single‐molecule to supramolecular properties. [ABSTRACT FROM AUTHOR]

Conjugated aromatic macrocycles are attractive due to their unique photophysical and optoelectronic properties. In particular, the cyclic radially oriented π‐system of cycloparaphenylenes (CPPs) gives rise to photophysical properties unlike any other small molecule or carbon nanomaterial. CPPs have tunable emission, possess large extinction coefficients, wide effective Stokes shifts, and high quantum yields. However, accessing bright CPPs with emissions beyond 500 nm remains difficult. Herein, we present a novel and bright orange‐emitting CPP‐based fluorophore showing a dramatic 105 nm red‐shift in emission and striking 237 nm effective Stokes shift while retaining a large quantum yield of 0.59. We postulate, and experimentally and theoretically support, that the quantum yield remains large due to the lack of intramolecular charge transfer. [ABSTRACT FROM AUTHOR]

Molecules and materials that demonstrate large amplitude responses to minor changes in their local environment play an important role in the development of new forms of nanotechnology. Molecular daisy chains are a type of a mechanically interlocked molecule that are particularly sensitive to such changes in which, in the presence of certain stimuli, the molecular linkage enables muscle‐like movement between a reduced‐length contracted form and an increased‐length expanded form. To date, all reported syntheses of molecular daisy chains are accomplished via passive‐template methods, resulting in a majority of structures being switchable only through the addition of an exogenous stimuli such as metal ions or changes in pH. Here, we describe a new approach to these structural motifs that exploits a multi‐component active‐metal template synthesis to mechanically interlock two pi‐rich nanohoop macrocycles into a molecular daisy chain that undergoes large conformational changes using thermal energy. [ABSTRACT FROM AUTHOR]

A new class of macrocyclic angle‐strained alkynes whose size and reactivity can be precisely tuned by modular organic synthesis is disclosed. Detailed analysis of the size‐dependent structural and electronic properties provides evidence for considerable distortion of the alkyne units incorporated into the cycloparaphenylene (CPP)‐derived macrocycles. The remarkable increase of the alkyne reactivity with decreasing macrocycle size in [2+2]cycloaddition–retrocyclization was investigated by joint experimental and theoretical studies and the thermodynamic and kinetic parameters that govern this reaction were unraveled. Additionally, even the largest, least strained macrocycle in this series was found to undergo strain‐promoted azide–alkyne cycloaddition (SPAAC) efficiently under mild conditions, thereby paving the way to the application of alkyne‐containing CPPs as fluorescent "clickable" macrocyclic architectures. Poised to react: Macrocyclic cycloparaphenylenes with built‐in alkynes are presented and the impact of strain on the structural/electronic properties of the alkyne investigated. The angle‐strained alkynes demonstrate a size‐dependent reactivity profile that permits [2+2]cycloaddition‐retrocyclization and copper‐free azide–alkyne coupling reactions under mild conditions. [ABSTRACT FROM AUTHOR]

Cycloparaphenylenes (CPPs) have attracted significant attention from theoretical, synthetic, supramolecular and material chemists owing to their aesthetical structures. Since Jasti and co‐workers reported the landmark synthesis of [9]CPP, [12]CPP and [18]CPP, the past ten years have witnessed a remarkable burst in the development of CPP research, from synthetic methodologies to the applications in optoelectronic devices. In this Focus Review, we highlight the representative synthetic strategies to CPPs and attempts on bottom‐up synthesis of carbon nanotubes (CNTs), and mainly focus on the optoelectronic properties studies of functionalized CPPs as well as heteroatoms doped CPP derivatives. Additionally, the potential applications of CPP derivatives in material science are discussed. Carbon nanohoops: Cycloparaphenylenes (CPPs) have attracted significant attention from theoretical, synthetic, supramolecular and material chemists in the past decade. This Focus Review highlights the representative synthetic strategies to CPPs, providing an overview of recent advances in the synthesis and property investigations of CPPs and its derivatives. The potential applications of CPPs have been discussed as well. [ABSTRACT FROM AUTHOR]

Abstract: The carbon–carbon (C−C) bond activation of [n]cycloparaphenylenes ([n]CPPs) by a transition‐metal complex is herein reported. The Pt0 complex Pt(PPh3)4 regioselectively cleaves two C−C σ bonds of [5] CPP and [6]CPP to give cyclic dinuclear platinum complexes in high yields. Theoretical calculations reveal that the relief of ring strain drives the reaction. The cyclic complex was further transformed into a cyclic diketone by using a CO insertion reaction. [ABSTRACT FROM AUTHOR]

Abstract: The complex of [10]cycloparaphenylene ([10]CPP) with bis(azafullerene) (C59N)2 is investigated experimentally and computationally. Two [10]CPP rings are bound to the dimeric azafullerene giving [10]CPP⊃(C59N)2⊂[10]CPP. Photophysical and redox properties support an electronic interaction between the components especially when the second [10]CPP is bound. Unlike [10]CPP⊃C60, in which there is negligible electronic communication between the two species, upon photoexcitation a partial charge transfer phenomenon is revealed between [10]CPP and (C59N)2 reminiscent of CPP‐encapsulated metallofullerenes. Such an alternative electron‐rich fullerene species demonstrates C60‐like ground‐state properties and metallofullerene‐like excited‐state properties opening new avenues for construction of functional supramolecular architectures with organic materials. [ABSTRACT FROM AUTHOR]

We perform a theoretical study on a set of carbon nanorings (CycloParaPhenylenes or CPP) envisioned as molecular templates for the selective synthesis of carbon nanotubes. The shape of these precursors, originating from bending n phenylene units in para position until forming the corresponding nanoring [ n ]CPP, may drive the growth of armchair single-walled nanotubes. This kinetic and thermodynamic study covers a set of molecules with different diameters, analyzing the exothermicity and the reaction path of a CPP-based radicaloid mechanism. The methodology employed is based on validated density functionals for mechanistic studies, shedding light on the viability of this synthetic pathway. [ABSTRACT FROM AUTHOR]

Bromination of [ n]cycloparaphenylenes (CPPs) is herein reported. Small [ n]CPPs ( n<8) underwent a bis-bromine addition reaction with high site selectively to produce tetrabromo adducts in moderate to excellent yields. Theoretical calculations revealed that thermodynamic stability dictates both the reactivity and site selectivity of the reaction. The addition product was further converted into the octabromo product by a FeBr3-catalyzed site-selective bromination reaction. The tetra- and octabromine adducts were then transformed into mono- to tetrabromo CPPs, which were further converted into several CPP derivatives. Therefore, bromination and subsequent transformations provide a path for late-stage functionalization of CPPs. [ABSTRACT FROM AUTHOR]

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 1H 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. [ABSTRACT FROM AUTHOR]

The electronic transport of [n]cycloparaphenylenes ([n]CPPs) is investigated based on nonequilibrium Green's function formalism in combination with the density-functional theory. Negative differential resistance (NDR) phenomenon is observed. Further analysis shows that the reduction of the transmission peak induced by the bias changing near Fermi energy results in the NDR effect. Replacing the electrode (from carbon chain to Au electrode), doping with N atom and changing the size of the nanohoop (n = 5, 6, 8, 10) have also been studied and the NDR still exists, suggesting the NDR behavior is the intrinsic feature of such [n]CPPs systems, which would be quite useful in future nanoelectronic devices. [ABSTRACT FROM AUTHOR]

This account describes synthetic approaches for curved polycyclic aromatics such as circulenes, helicenes and cycloparaphenylenes, relying on a [2+2+2] cycloaddition. A common feature of all these structures is that their synthesis needs to deviate benzene rings from planarity. Relying on [2+2+2] cycloaddition reactions for this task leads to impressive, and in parts, surprising results. The examples shown here and their optimized reaction conditions contribute to a better understanding of processes going on during the reaction. This knowledge is expected to lead to new designs of challenging syntheses using the [2+2+2] cycloaddition methodology. 1 No Gain, No Strain: Synthesis of Curved Aromatics 2 Examples for the Preparation of Strained Systems Relying on a [2+2+2] Cycloaddition 2.1 Circulenes 2.2 Helicenes 2.3 Cycloparaphenylenes 3 Conclusion and Outlook. [ABSTRACT FROM AUTHOR]

The synthesis of alternating donor-acceptor [12] and [16]cycloparaphenylenes (CPPs) has been achieved by the rhodium-catalyzed intermolecular cross-cyclotrimerization followed by imidation and/or aromatization. These alternating donor-acceptor CPPs showed positive solvatofluorochromic properties and smaller HOMO-LUMO gaps compared with nonfunctionalized CPPs, which was confirmed by the theoretical study. [ABSTRACT FROM AUTHOR]

Nanoscale carbon-rich molecular architectures are not only aesthetically appealing but also of practical importance for energy and biomedical technologies. Herein, we report the synthesis of cyclic-oligophenylene-based nanopropeller 1 by using an efficient synthon strategy involving sequential intramolecular bisboronate homocoupling and reductive aromatization by H2SnCl4. The nanopropeller molecules pack into a layered hexagonal lattice featuring long-ranged nano-sized channels and a total guest-accessible volume of 48 %, as revealed by X-ray diffraction studies. We suggest that such a solid-state arrangement is determined by the interplay between the propeller architecture and the intermolecular van der Waals interactions. [ABSTRACT FROM AUTHOR]

Synthetic pathways to furan-containing cycloparaphenylenes (CPPs) as molecular nanohoops bearing 10, 12, and 15 aromatic units including furan-2,5-diyl or 2,2'-bifuran-5,5'-diyl units have been developed. The X-ray structures of a partially hydrogenated bifuran-containing CPP precursor and the corresponding fully aromatized bifuran-containing CPP were obtained to allow the determination of their conformational arrangements in the crystal lattice. The optical and electrochemical properties of the furan-containing CPPs were investigated. [ABSTRACT FROM AUTHOR]

We have synthesized a cycloparaphenylene containing a perylene motif that is a model for a carbon nanotube sidewall. The reactivity of the sidewall model towards a Diels–Alder reaction using a masked acetylene was examined and similar reactivity was observed between the macrocyclic and planar substrate. This study suggests that a Diels–Alder reaction is a viable method for carbon nanotube growth using an appropriate template. [ABSTRACT FROM AUTHOR]

The oxidation processes of [ n]cycloparaphenylenes ([ n]CPPs) ( n=5-12) were systematically investigated by cyclic and rotating disk electrode voltammetry. All CPPs underwent pseudo-reversible two-electron oxidation irrespective of ring size, forming the corresponding radical cations and then dications. The results were in sharp contrast to those observed for linear oligoparaphenylenes, which only undergo one-electron oxidation. The difference in the first and second oxidation potentials in the CPP oxidation was affected by the ring size and became more significant as the decrease of CPP size. In other words, while the first oxidation from neutral CPP to the radical cation occurred faster as the size of CPP becomes smaller, the second oxidation from the radical cation to dication exhibited opposite size dependence. [ABSTRACT FROM AUTHOR]

Mono- and multinuclear complexes of ruthenium and [n]cycloparaphenylene (CPP, n=5 and 6) were synthesized in excellent yields through ligand exchange of the cationic complex [(Cp)Ru(CH3CN)3](PF6) with CPP. In the multinuclear complexes, ruthenium selectively coordinated to alternate paraphenylene units to give bis- and tris-coordinated Ru complexes for [5] and [6]CPPs, respectively. Single-crystal Xray analysis revealed the Ru was coordinated with η6-hapticity on the convex surface of CPP. [ABSTRACT FROM AUTHOR]

Mono- and multinuclear complexes of ruthenium and [n]cycloparaphenylene (CPP, n = 5 and 6) were synthesized in excellent yields through ligand exchange of the cationic complex [(Cp)Ru(CH3CN)3](PF6) with CPP. In the multinuclear complexes, ruthenium selectively coordinated to alternate paraphenylene units to give bis- and tris-coordinated Ru complexes for [5] and [6]CPPs, respectively. Single-crystal Xray analysis revealed the Ru was coordinated with η6-hapticity on the convex surface of CPP. [ABSTRACT FROM AUTHOR]