Concise Synthesis and Crystal Structure of [12]Cycloparaphenylene

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.

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.

Synthesis and metalation of polycatechol nanohoops derived from fluorocycloparaphenylenes

Due to their unique topology and distinct physical properties, cycloparaphenylenes (CPPs) are attractive building blocks for new materials synthesis. While both noncovalent interactions and irreversible covalent bonds have been used to link CPP monomers into extended materials, a coordination chemistry approach remains less explored. Here we show that nucleophilic aromatic substitution reactions can be leveraged to rapidly introduce donor groups (-OR, -SR) onto polyfluorinated CPP rings. Demethylation of methoxide-substituted CPPs produces polycatechol nanohoop ligands that are readily metalated to produce well-defined, multimetallic CPP complexes. As catechols are recurring motifs throughout coordination chemistry and dynamic covalent chemistry, the polycatechol nanohoops reported here open the door to new strategies for the bottom-up synthesis of atomically precise CPP-based materials.

Charge delocalization and aromaticity of doubly reduced double-walled carbon nanohoops

Cycloparaphenylenes (CPPs) exhibit selective host capabilities, featuring the ability to incorporate smaller CPPs to form double-walled host-guest complexes. Moreover, CPPs can also be stabilized by global aromaticity under twofold oxidation or reduction, involving electronic conjugation along with the overall structural backbone. Herein we explore the structural modifications, bonding, electron delocalization and magnetic properties of doubly reduced double-walled CPP complexes with DFT methods, in the isolated and aggregate [n + 5]CPP⊃[n]CPP^2- (n = 5-8) species. Our results show that the hosts undergo structural, bonding and delocalization deformations towards quinoidal configurations and exhibit global long-ranged shielding cones similar to global aromatic free dianionic CPPs, accounting for charge delocalization on the outer nanohoops, whereas the guests preserve local aromatic benzenoid configurations, resulting in global and local aromatic circuits within the host-guest aggregate. This observation suggests that in multi-layered related species electronic delocalization will be retained at the outer structural surface. The aromaticity of the hosts is manifested in the strong upfield shifts of the guests ¹H-NMR signals. Hence, CPP complexes can be extended to doubly reduced species stabilized by global host aromaticity expanding our understanding of doubled-walled nanotubes at the nanoscale regime.

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 .

Perfluorocycloparaphenylenes

Perfluorinated aromatic compounds, the so-called perfluoroarenes, are widely used in materials science owing to their high electron affinity and characteristic intermolecular interactions. However, methods to synthesize highly strained perfluoroarenes are limited, which greatly limits their structural diversity. Herein, we report the synthesis and isolation of perfluorocycloparaphenylenes (PFCPPs) as a class of ring-shaped perfluoroarenes. Using macrocyclic nickel complexes, we succeeded in synthesizing PF[n]CPPs (n = 10, 12, 14, 16) in one-pot without noble metals. The molecular structures of PF[n]CPPs (n = 10, 12, 14) were determined by X-ray crystallography to confirm their tubular alignment. Photophysical and electrochemical measurements revealed that PF[n]CPPs (n = 10, 12, 14) exhibited wide HOMO–LUMO gaps, high reduction potentials, and strong phosphorescence at low temperature. PFCPPs are not only useful as electron-accepting organic materials but can also be used for accelerating the creation of topologically unique molecular nanocarbon materials.

Synthetic methods for the preparation of perfluorinated aromatic compounds are desirable in materials science. Here, the authors synthesize perfluorocycloparaphenylenes, fully fluorinated carbon nanorings, through a nickel-mediated one-pot method.

Planar π-extended cycloparaphenylenes featuring an all-armchair edge topology

The [n]cycloparaphenylenes ([n]CPPs)-n para-linked phenylenes that form a closed-loop-have attracted substantial attention due to their unique cyclic structure and highly effective para-conjugation leading to a myriad of fascinating electronic and optoelectronic properties. However, their strained topology prevents the π-extension of CPPs to convert them either into armchair nanobelts or planarized CPP macrocycles. Here we successfully tackle this long-standing challenge and present the bottom-up synthesis and characterization of atomically precise in-plane π-extended [12]CPP on Au(111) by low-temperature scanning probe microscopy and spectroscopy combined with density functional theory. The planar π-extended CPP is a nanographene with an all-armchair edge topology. The exclusive para-conjugation at the periphery yields delocalized electronic states and the planarization maximizes the overlap of p orbitals, which both reduce the bandgap compared to conventional CPPs. Calculations predict ring currents and global aromaticity in the doubly charged system. The intriguing planar ring topology and unique electronic properties make planar π-extended CPPs promising quantum materials.

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.

Splitting the Ring: Impact of Ortho and Meta Pi Conjugation Pathways through Disjointed [8]Cycloparaphenylene Electronic Materials

In this report, we describe the synthesis and electronic properties of small-molecule and polymeric [8]cycloparaphenylenes ([8]CPPs) with disjointed pi-conjugated substituents. Arylene-ethynylene linkers were installed on opposite sides of the [8]CPP nanohoop as separated by three phenyl units on either side such that the monomer systems have syn (C₂ symmetry) and anti (C₁ symmetry) conformers with a small energy gap (0.1-0.6 kcal/mol). This disjoined substitution pattern necessarily forces delocalization through and around the CPP radial structure. We demonstrate new electronic states from this radial/linear mixing in both the small molecules and the pi extended polymers. Quantum chemical calculations reveal that these electronic processes arise from multiple operative radial/linear conjugation pathways, as the disjoint pattern results in both ortho and meta connections to the CPP ring. These results affirm the unique nature of hybrid radial and linear pi electron delocalization operative in these new conjugation pathways.

Synthesis, Structures and Fluorescence Properties of gem-Linked Cyclic Tetraphenylethylenes and Cyclic hexaphenylethylenes

Rigid cyclic molecules are of great interest due to their intriguing structures and unique properties. Here, we report the facile synthesis of gem-linked cyclic tetraphenylethylenes and cyclic hexaphenylethylenes, namely [n]CTPEs...

Chemical Tuning of Exciton versus Charge-Transfer Excited States in Conformationally Restricted Arylene Cages

Covalent assemblies of conjugated organic chromophores provide the opportunity to engineer new excited states with novel properties. In this work, a newly developed triple-stranded cage architecture, in which meta-substituted aromatic caps serve as covalent linking groups that attach to both top and bottom of the conjugated molecule walls, is used to tune the properties of thiophene oligomer assemblies. Benzene-capped and triazine-capped 5,5'-(2,2-bithiophene)-containing arylene cages are synthesized and characterized using steady-state and time-resolved spectroscopic methods. The conformational freedom and electronic states are analyzed using time-dependent density functional theory. The benzene cap acts as a passive spacer whose electronic states do not mix with those of the chromophore walls. The excited state properties are dominated by through-space interactions between the chromophore subunits, generating a neutral Frenkel H-type exciton state. This excitonic state undergoes intersystem crossing on a 200 ps time scale while the fluorescence output is suppressed by a factor of 2 due to a decreased radiative rate. Switching to a triazine cap enables electron transfer from the chromophore-linker after the initial excitation to the exciton state, leading to the formation of a charge-transfer state within 10 ps. This state can avoid intersystem crossing and exhibits red-shifted fluorescence with enhanced quantum yield. The ability to interchange structural modules with different electronic properties while retaining the overall cage morphology provides a new approach for tuning the properties of discrete chromophore assemblies.

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

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

Stretching [8]cycloparaphenylene with encapsulated potassium cations: structural and theoretical insights into core perturbation upon four-fold reduction and complexation

The consequences of four-electron addition to [8]cycloparaphenylene ([8]CPP, 1) have been evaluated crystallographically, revealing a significant core deformation. The structural analysis exposes an elliptical distortion observed upon electron transfer, with the deformation parameter (D.P.) increased by 28% in comparison with neutral [8]CPP. The C-C bond length alteration pattern also indicates a quinoidal structural rearrangement upon four-fold reduction. The large internal cavity of [8]CPP4- allows the encapsulation of two {K+(THF)2} cationic moieties with two additional cations bound externally in the solid-state structure of [{K+(THF)2}4([8]CPP4-)]. The experimental structural data have been used as a benchmark for the comprehensive theoretical description of the geometric changes and electronic properties of the highly-charged [8]CPP4- nanohoop in comparison with its neutral parent. While neutral [8]CPP and the [8]CPP2- anion clearly show aromatic behavior of all six-membered rings, subsequent addition of two more electrons completely reverses their aromatic character to afford the highly-antiaromatic [8]CPP4- anion, as evidenced by structural, topological, and magnetic descriptors. The disentanglement of electron transfer from metal binding effects allowed their contributions to the overall core perturbation of the negatively-charged [8]CPP to be revealed. Consequently, the internal coordination of potassium cations is identified as the main driving force for drastic elliptic distortion of the macrocyclic framework upon reduction.

Structural deformation and host-guest properties of doubly-reduced cycloparaphenylenes, [n]CPPs2- (n = 6, 8, 10, and 12)

Chemical reduction of several cycloparaphenylenes (CPPs) ranging in size from [8]CPP to [12]CPP has been investigated with potassium metal in THF. The X-ray diffraction characterization of the resulting doubly-reduced [n]CPPs provided a unique series of carbon nanohoops with increasing dimensions and core flexibility for the first comprehensive structural analysis. The consequences of electron acquisition by a [n]CPP core have been analyzed in comparison with the neutral parents. The addition of two electrons to the cyclic carbon framework of [n]CPPs leads to the characteristic elliptic core distortion and facilitates the internal encapsulation of sizable cationic guests. Molecular and solid-state structure changes, alkali metal binding and unique size-dependent host abilities of the [n]CPP^2- series with n = 6-12 are discussed. This in-depth analysis opens new perspectives in supramolecular chemistry of [n]CPPs and promotes their applications in size-selective guest encapsulation and chemical separation.

Photoexcited energy relaxation and vibronic couplings in π-conjugated carbon nanorings

Conjugated carbon nanorings exhibit unique photophysical properties that, combined with their tunable sizes and conformations, make them suitable for a variety of practical applications. These properties are intimately associated to their strained, bent and sterically hindered cyclic structures. Herein we perform a comparative analysis of the photoinduced dynamics in carbon nanorings composed of nine phenyl units([9]CPP) and nine naphthyl units ([9]CN) respectively. The sterically demanding naphthyl units lead to large dihedral angles between neighboring units. Nevertheless, the ultrafast electronic and vibrational energy relaxation and redistribution is found to be similar for both systems. We observe that vibronic couplings, introduced by nonadiabatic energy transfer between electronic excited states, ensure the intramolecular vibrational energy redistribution through specific vibrational modes. The comparative impact of the internal conversion process on the exciton spatial localization and intra-ring migration indicates that naphthyl units in [9]CN achieve more efficient but less dynamical self-trapping compared to that of phenyl units in [9]CPP. That is, during the photoinduced process, the exciton in [9]CN is more static and localized than the exciton in [9]CPP. The internal conversion processes take place through a specific set of middle- to high-frequency normal modes, which directly influence the spatial exciton redistribution during the internal conversion, self-trapping and intra-ring migration.

Electronic Energy Relaxation in a Photoexcited Fully Fused Edge-Sharing Carbon Nanobelt

Carbon nanobelts are cylindrical molecules composed of fully fused edge-sharing arene rings. Because of their aesthetically appealing structures, they acquire unusual optoelectronic properties that are potentially suitable for a range of applications in nanoelectronics and photonics. Nevertheless, the very limited success of their synthesis has led to their photophysical properties remaining largely unknown. Compared to that of carbon nanorings (arenes linked by single bonds), the strong structural rigidity of nanobelts prevents significant deformations away from the original high-symmetry conformation and, therefore, impacts their photophysical properties. Herein, we study the photoinduced dynamics of a successfully synthesized belt segment of (6,6)CNT (carbon nanotube). Modeling this process with nonadiabatic excited state molecular dynamics simulations uncovers the critical role played by the changes in excited state wave function localization on the different types of carbon atoms. This allows a detailed description of the excited state dynamics and spatial exciton evolution throughout the nanobelt scaffold. Our results provide detailed information about the excited state electronic properties and internal conversion rates that is potentially useful for designing nanobelts for nanoelectronic and photonic applications.

Highly Selective Anion Template Effect in the Synthesis of Constrained Pseudopeptidic Macrocyclic Cyclophanes

Herein, we report the synthesis of a novel family of constrained pseudopeptidic macrocyclic compounds containing the hexahydropyrrolo[3,4-f]isoindolocyclophane scaffold and involving four coupled substitution reactions in the macrocyclization process. Although the increase in the number of steps involved in the macrocyclization could lead to a larger number of possible side products, the optimization of the methodology and the study of the driving forces have made it possible to obtain the desired macrocycles in excellent yields. A thorough computational study has been carried out to understand the macrocyclization process, and the results obtained nicely agree with experimental data. Moreover, the bromide anion had a clear catalytic template effect in the macrocyclization reaction, and surprisingly, the chloride anion had a negative template effect in opposition to the results obtained for analogous macrocycles. The parameters responsible for the specific kinetic template effect observed have been studied in detail.

Linear, Non-Conjugated Cyclic and Conjugated Cyclic Paraphenylene under Pressure

The n-paraphenylene family comprises chains of phenylene units linked together by C-C bonds that are between single- and double-bonded, and where n corresponds to the number of phenylene units. In this work, we compare the response of the optical properties of different phenylene arrangements. We study linear chains (LPP), cyclic systems (CPPs), and non-conjugated cyclic systems with two hydrogenated phenylenes (H₄[n]CPP). Particularly, the systems of interest in this work are [6]LPP, [12]- and [6]CPP and H₄[6]CPP. This work combines Raman and infrared spectroscopies with absorption and fluorescence (one- and two-photon excitations) measured as a function of pressure up to maximum of about 25 GPa. Unprecedented crystallographic pressure-dependent results are shown on H₄[n]CPP, revealing intramolecular π-π interactions upon compression. These intramolecular interactions justify the H₄[n]CPP singular optical properties with increasing fluorescence lifetime as a function of pressure.

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.

Inference-assisted intelligent crystallography based on preliminary data

Crystal structure analysis is routinely used to determine atomically resolved molecular structures and structure-property relationships. The accumulation of reliable structural characteristics obtained by crystal structure analysis has forged a robust basis that is frequently used in molecular and materials sciences. However, experimental techniques remain hampered by time-consuming ‘blind’ measurement-analysis iterations, which are sometimes required to find appropriate crystals and experimental conditions. Herein, we present a method that uses a small preliminary data set to evaluate the to-be-observed structures and the to-be-collected data. Moreover, we demonstrate the practical utility of this method to improve the efficiency of crystal structure analysis. This method will help selecting suitable crystals and choosing favorable experimental conditions to generate results that satisfy the level of precision required for specific research objectives.

Synthesis, Characterization, and Solid-State Structure of [8]Cycloparaphenylenes with Inherent Chirality

We report here the synthesis of two [8]cycloparaphenylenes ([8]CPP) derivatives, 1 and 2, bearing a monosubstituted benzene moiety. The presence of the substituent implies a planar chirality for the monosubstituted [8]CPP 1 and 2, whose configuration is here described by applying the chirality descriptors pR and pS. Experimental evidence of this planar chirality has been obtained through ¹H VT NMR studies and by addition of Pirkle's reagent. This was confirmed by the X-ray crystal structure of 2, which represents an interesting example of solid-state structure of a monosubstituted [8]CPP derivative. Derivative 2 crystallizes in two monoclinic crystal forms (α and β), which show a herringbone motif. The [8]CPP ring of the α form encapsulates two dichloromethane molecules, held through C-H···π interactions, while in the β form, open channels are partially filled by highly disordered solvent molecules.

Triple Helical Ir(ppy)3 Phenylene Cage Prepared by Diol-Mediated Benzannulation: Synthesis, Resolution, Absolute Stereochemistry and Photophysical Properties

Cyclometalation of a triple helical N-doped phenylene cage prepared by ruthenium(0)-catalyzed diol-diene benzannulation delivers a chiral, conformationally constrained Ir(ppy)₃ analogue. Like the parent complex, fac-Ir(ppy)₃ , the iridium-containing PAH-cage is phosphorescent, but displays enhanced resistance to oxygen quenching.

Charge transport parameters for carbon based nanohoops and donor-acceptor derivatives

The effect of donor-acceptor (D-A) moieties on magnitudes such as reorganization energies and electronic couplings in cycloparaphenylene (CPP) carbon based nanohoops (i.e. conjugated organic molecules with cyclic topology) is highlighted via model computations and analysis of the available crystalline structure of N,N-dimethylaza[8]CPP. For the sake of comparison, intra-molecular and inter-molecular charge transport parameters are concomitantly modelled for the recently determined herringbone polymorph of [6]CPP, along with [8]CPP and [12]CPP. The peculiar contribution of low frequency vibrations to intramolecular reorganization energies is also disclosed by computing the Huang-Rhys factors for the investigated [n]CPPs and the N,N-dimethylaza derivative. In contrast with most planar organic semiconductors where the layer in which molecules are herringbone arranged identifies the high-mobility plane, nanohoops disclose inter-layer electronic couplings larger than the intra-layer counterparts. Charge transfer rate constants modelled with three different approaches (Marcus, Marcus-Levich-Jortner and spectral overlap) suggest that D-A nanohoops, owing to orbital localization, may be more efficient for charge transport than [n]CPPs for suitable solid phase arrangements.

Preparation of a large-sized highly flexible carbon nanohoop

A highly flexible carbon nanohoop composed of HBC panels was prepared by connection together with biphenylene spacers.

Rational Design of Efficient Environmental Sensors: Ring-Shaped Nanostructures Can Capture Quat Herbicides

The viability of using [n]-cycloparaphenylenes (CPPs) of different sizes to encapsulate diquat (DQ) pesticide molecules has been tested analyzing the origin of the host-guest interactions stabilizing the complex. This analysis provides rational design capabilities to construct ad hoc capturing systems tailored to the desired pollutant. All CPPs considered (n = 7-12) are capable of forming remarkably stable complexes with DQ, though [9]-CPP is the best candidate, where a fine balance is established between the energy penalty due to the deformation + repulsion of the pesticide molecule inside the cavity (larger in smaller CPPs) and the maximization of the favorable dispersion, electrostatic and induction contributions (which also decrease in larger rings). These encouraging results prompted us to evaluate the potential of using Resonance Raman spectroscopy on nanohoop complexes as a tool for DQ sensing. The shifts observed in the vibrational frequencies of DQ upon complexation allow us to determine whether complexation has been achieved. Additionally, a large enhancement of the signals permits a selective identification of the vibrational modes.

Solid-State Order and Charge Mobility in [5]- to [12]Cycloparaphenylenes

We report a computational study of mesoscale morphology and charge-transport properties of radially π-conjugated cycloparaphenylenes ([ n]CPPs) of various ring sizes ( n = 5-12, where n is the number of repeating phenyl units). These molecules are considered structural constituents of fullerenes and carbon nanotubes. [ n]CPP molecules are nested in a unique fashion in the solid state. Molecular dynamics simulations show that while intramolecular structural stability (order) increases with system size, intermolecular structural stability decreases. Density functional calculations reveal that reorganization energy, an important parameter in charge transfer, decreases as n is increased. Intermolecular charge-transfer electronic couplings in the solid state are relatively weak (due to curved π-conjugation and loose intermolecular contacts) and are on the same order of magnitude (∼10 meV) for each system. Intrinsic charge-carrier mobilities were simulated from kinetic Monte Carlo simulations; hole mobilities increased with system size and scaled as ∼ n⁴. We predict that disordered [ n]CPPs exhibit hole mobilities as high as 2 cm²/(V·s). Our computations show a strong correlation between reorganization energy and hole mobility (μ ∼ λ^-4). Quantum mechanical calculations were performed on cofacially stacked molecular pairs for varying phenyl units and reveal that orbital delocalization is responsible for both decreasing reorganization energies and electronic couplings as n is increased.

A Bottom-Up Approach to Solution-Processed, Atomically Precise Graphitic Cylinders on Graphite

Extended carbon nanostructures, such as carbon nanotubes (CNTs), exhibit remarkable properties but are difficult to synthesize uniformly. Herein, we present a new class of carbon nanomaterials constructed via the bottom-up self-assembly of cylindrical, atomically precise small molecules. Guided by supramolecular design principles and circle packing theory, we have designed and synthesized a fluorinated nanohoop that, in the solid state, self-assembles into nanotube-like arrays with channel diameters of precisely 1.63 nm. A mild solution-casting technique is then used to construct vertical "forests" of these arrays on a highly ordered pyrolytic graphite (HOPG) surface through epitaxial growth. Furthermore, we show that a basic property of nanohoops, fluorescence, is readily transferred to the bulk phase, implying that the properties of these materials can be directly altered via precise functionalization of their nanohoop building blocks. The strategy presented is expected to have broader applications in the development of new graphitic nanomaterials with π-rich cavities reminiscent of CNTs.

Influence of Molecular Conformation on Electron Transport in Giant, Conjugated Macrocycles

We describe here the direct connection between the molecular conformation of a conjugated macrocycle and its macroscopic charge transport properties. We incorporate chiral, helical perylene diimide ribbons into the two separate macrocycles as the n-type, electron transporting material. As the macrocycles' films and electronic structures are analogous, the important finding is that the macrocycles' molecular structures and their associated dynamics determine device performance in organic field effect transistors. We show the more flexible macrocycle has a 4-fold increase in electron mobility in field effect transistor devices. Using a combination of spectroscopy and density functional theory calculations, we find that the origin of the difference in device performance is the ability of more flexible isomer to make intermolecular contacts relative to the more rigid counterpart.

Hollow organic capsules assemble into cellular semiconductors

Self-assembly of electroactive molecules is a promising route to new types of functional semiconductors. Here we report a capsule-shaped molecule that assembles itself into a cellular semiconducting material. The interior space of the capsule with a volume of ~415 ų is a nanoenvironment that can accommodate a guest. To self-assemble these capsules into electronic materials, we functionalize the thiophene rings with bromines, which encode self-assembly into two-dimensional layers held together through halogen bonding interactions. In the solid state and in films, these two-dimensional layers assemble into the three-dimensional crystalline structure. This hollow material is able to form the active layer in field effect transistor devices. We find that the current of these devices has strong response to the guest’s interaction within the hollow spaces in the film. These devices are remarkable in their ability to distinguish, through their electrical response, between small differences in the guest.

Perylene diimide-bithiophene macrocycles are electroactive and shape-persistent hosts. Here, the authors describe their self-assembly into a cellular organic semiconducting film whose voids are electrically sensitive to different guests, and which can function as the active layer in a field-effect transistor device.

Nitrogen doped nanohoops as promising CO2 capturing devices

The impact of climate change in the face of steady or increasing emissions has made the capture and storage of CO2 a priority issue. Supramolecular chemistry is one of the tools that can be used for this task, due to the possibility of tuning intermolecular interactions for the capture of this gas in a selective and efficient way. In this context, this work presents a novel approach for the capture of CO2 based on n-cycloparaphenylenes ([n]-CPPs) doped with nitrogen atoms. This is the first time that the potential of these structures for the capture of polluting gases has been evaluated. Among all the structures analysed, the one yielding the best results (complexation energy of -32.80 kJ mol-1) contains 4 nitrogen atoms per monomer. The topology of the electron density of the host-guest complex and the nature of its non-covalent interactions have been analyzed in this work in order to explain this high binding energy and identify potential structural modifications to improve it. The capability of this system to be used as a sensing device for CO2 using vibrational spectroscopy is also explored.