Fullerene Guests Research Articles

Enhancing Effect of Fullerene Guest and Counterion on the Structural Stability and Electrical Conductivity of Octahedral Metallo-Supramolecular Cages.

Metallo-supramolecular cages have garnered tremendous attention for their diverse yet molecular-level precision structures. However, the physical properties of these supramolecular ensembles, which are of potential significance in molecular electronics, remain largely unexplored. We herein constructed a series of octahedral metallo-cages and cage-fullerene complexes with notably enhanced structural stability. As such, we could systematically evaluate the electrical conductivity of these ensembles at both the single-molecule level and aggregated bulk state (as well-defined films). Our findings reveal that counteranions and fullerene guests play a pivotal role in determining the electrical conductivity of the aggregated state, while such effects are less significant for single-molecule conductance. Both the counteranions and fullerenes effectively tune the electronic structures and packing density of metallo-supramolecular assemblies, and facilitate efficient charge transfer between the cage hosts and fullerenes, resulting in a notable one order of magnitude increase in the electrical conductivity of the aggregated state.

Enhancing Effect of Fullerene Guest and Counterion on the Structural Stability and Electrical Conductivity of Octahedral Metallo‐Supramolecular Cages

Metallo‐supramolecular cages have garnered tremendous attention for their diverse yet molecular‐level precision structures. However, physical properties of these supramolecular ensembles, which are of potential significance in molecular electronics, remain largely unexplored. We herein constructed a series of octahedral metallo‐cages and cage‐fullerene complexes with notably enhanced structural stability. As such, we could systematically evaluate the electrical conductivity of these ensembles at both single‐molecule level and aggregated bulk state (as well‐defined films). Our findings reveal that counteranions and fullerene guests play a pivotal role in determining the electrical conductivity of aggregated state, while such effects are less significant for single‐molecule conductance. Both counteranions and fullerenes effectively tune the electronic structures and packing density of metallo‐supramolecular assemblies, and facilitate efficient charge transfer between the cage hosts and fullerenes, resulting in a notable one order of magnitude increase in electrical conductivity of the aggregated state.

Tethered Helical Ladder-Type Aromatic Lactams.

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

Insight into the interaction of host-guest structures for pyrrole-based metal compounds and C70.

This study focuses on the recognition and isolation of fullerenes, which are crucial for further exploration of their physical and chemical properties. Our goal is to investigate the potential recognition of the D5h-C70 fullerene using crown-shaped metal compositions through density functional theory calculations. We assess the effectiveness of fullerene C70 recognition by studying the binding energy. Additionally, various analyses were conducted, including natural bond order charge analysis and reduced density gradient analysis, to understand the interaction mechanism between the host and guest molecules. These investigations provide valuable insights into the nature of the interaction and the stability of the host-guest system. To facilitate the release of the fullerene guest molecule, the vis-NIR spectra were simulated for the host-guest structures. This analysis offers guidance on the specific wavelengths that can be utilized to release the fullerene guest from the host-guest structures. Overall, this work proposes a new strategy for the effective recognition of various fullerene molecules and their subsequent release from host-guest systems. These findings could potentially be applied in assemblies involving fullerenes, advancing their practical applications.

A Conjugated Phenylene Nanocage with a Guest-Adaptive Deformable Cavity.

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

A Conjugated Phenylene Nanocage with a Guest‐Adaptive Deformable Cavity

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

Selective recognition and enrichment of C70 over C60 using an anthracene-based nanotube.

Selective recognition and enrichment of fullerenes (e.g., C60 and C70) remains challenging due to the same diameter and geometrical similarity. Herein, we report a hexagonal anthracene-based nanotube (1) through a one-pot Suzuki-Miyaura cross-coupling reaction. With anthracene-based side walls and pyridine linkers, 1 features a nano-scale tubular cavity measuring 1.2 nm in diameter and 0.9 nm in depth, along with pH-responsive properties. Interestingly, the electron-rich 1 shows high binding affinity (K a ≈ 106 M-1) and selectivity (K s ≈ 140) to C70 over C60 in toluene, resulting from their different contribution of π-π interactions with the host. The protonation of 1 simultaneously alters the electronic properties within the nanotube, resulting in the release of the fullerene guests. Lastly, the selective recognition and pH stimuli-responsive properties of the nanotube have been utilized to enrich C70 from its low-content mixtures of fullerenes in chloroform.

Dynamically switchable porphyrin-based molecular tweezer for on−off fullerene recognition

Herein, a novel molecular tweezer based on 2,2′-bipyridine-bridged porphyrin subunits was constructed for efficient fullerenes recognition. The syn conformation of the molecule, which was obtained by Zn(Ⅱ) coordination, gives rise to a proper cavity to interact with fullerene guests to form a stable 1:1 complex in toluene solution. It exhibits distinct binding selectivity towards C60 over C70. Moreover, the fullerene recognition capacity can be adequately suppressed by importing H2PO4− to competitively capture Zn(Ⅱ) along with syn-anti conformational conversion. Subsequently, the molecular tweezer regenerated to bind the fullerene by introducing the Ca2+ into the system. Significantly, the association-disassociation process can be switched reversibly and repeatedly.

Metal Atoms (Li, Na, and K) Tuning the Configuration of Pyrrole for the Selective Recognition of C60

Host-guest structure assembly is significant in the recognition of molecules, and the fullerene-based host-guest structure is a convenient method to determine the structures of fullerenes of which recognition is with many difficulties in experiments. Here, with density functional theory calculations, we designed several crown-shaped pyrrole-based hosts tuned by doping metal atoms (Li, Na, and K) for the effective recognition of C60 with modest interaction between the host and guest. Binding energy calculations showed an enhanced interaction of the concave-convex host-guest system with the doped metal atoms, enabling the selective recognition of C60. The electrostatic interaction between the host and guest was studied by the natural bond order charge analysis, reduced density gradient, and electrostatic potential. Furthermore, the UV-vis-NIR spectra of host-guest structures were simulated to give guidance on the release of the fullerene guest. With much expectation, this work would give a new strategy to design new hosts for effectively recognizing much more fullerene molecules with modest interaction and would be useful for the assembly involving fullerenes.

Balancing Attraction and Repulsion: The Influence of London Dispersion in [10]Cycloparaphenylene-Fullerene Complexes.

Herein we present a systematic study of the influence of different alkyl chains in malonyl ester fullerene adducts with [10]cycloparaphenylene ([10]CPP]) and a tert-butyl (tBu) ester-substituted [10]CPP analogue. The association constants between the nanoring hosts and the fullerene guests were determined by fluorescence quenching experiments. The trends in association were rationalized by an interplay of repulsion arising from an extended volume and London dispersion as an attractive counterpart.

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.

Tetrathiafulvalene and π-extended tetrathiafulvalene pillar[5]arene conjugates: synthesis, electrochemistry and host–guest properties

Pillar[5]arene derivatives decorated with ten peripheral TTF or exTTF subunits were prepared and their electrochemical properties investigated. These electron-rich macrocyclic systems are suitable receptors for a fullerene guest.

Fullerene Complexation in a Hydrogen-Bonded Porphyrin Receptor via Induced-Fit: Cooperative Action of Tautomerization and C-H···π Interactions.

A supramolecular chiral hydrogen-bonded tetrameric aggregate possessing a large cavity and tetraarylporphyrin substituents was assembled using alternating 4H- and 2H-bonds between ureidopyrimidinone and isocytosine units, respectively. The aggregation mode was rationally shifted from social to narcissistic self-sorting by changing urea substituent size only. The H-bonded tetramer forms a strong complex with C60 guest, at the same time undergoing remarkable structural changes. Namely, the cavity adjusts to the guest via keto-to-enol tautomerization of the ureidopyrimidinone unit and as a result, porphyrin substituents move apart from each other in a scissor blade-like opening fashion. The rearrangement is accompanied by C-H···π interaction between the alkyl solubilizing groups and the nearby placed porphyrin π-systems. The latter interaction was found to be crucial for the guest complexation event, providing energetic compensation for otherwise costly tautomerization. We showed that only the systems possessing sufficiently long alkyl chains capable of interacting with a porphyrin ring are able to form a complex with C60. The structural rearrangement of the tetramer was quantitatively characterized by electron paramagnetic resonance pulsed dipolar spectroscopy measurements using photogenerated triplets of porphyrin and C60 as spin probes. Further exploring the C-H···π interaction as a decisive element for the C60 recognition, we investigated the guest-induced self-sorting phenomenon using scrambled tetramer assemblies composed of two types of monomers possessing alkyl chains of different lengths. The presence of the fullerene guest has enabled the selective scavenging of monomers capable of C-H···π interaction to form homo-tetrameric aggregates.

Exploring the Gas-Phase Formation and Chemical Reactivity of Highly Reduced M8 L6 Coordination Cages.

Coordination cages with well-defined cavities show great promise in the field of catalysis on account of their unique combination of molecular confinement effects and transition-metal redox chemistry. Here, three coordination cages are reduced from their native 16+ oxidation state to the 2+ state in the gas phase without observable structural degradation. Using this method, the reaction rate constants for each reduction step were determined, with no noticeable differences arising following either the incorporation of a C60 -fullerene guest or alteration of the cage chemical structure. The reactivity of highly reduced cage species toward molecular oxygen is "switched-on" after a threshold number of reduction steps, which is influenced by guest molecules and the structure of cage components. These new experimental approaches provide a unique window to explore the chemistry of highly-reduced cage species that can be modulated by altering their structures and encapsulated guest species.

C–H⋯S Hydrogen Bond Assisted Supramolecular Encapsulation of Fullerenes with Nanobelts

C–H⋯S Hydrogen Bond Assisted Supramolecular Encapsulation of Fullerenes with Nanobelts

Photophysical Properties of Naphthalene-oxacalix[m]arene and Recognition of Fullerene C60.

Three different pore sizes of oxacalix[m]arene[n]pyrimidines modified with a naphthalene substituent were synthesized and characterized by HRMS, 1H NMR, and single-crystal analysis (8OA and 8OA-N). Steady-state spectroscopy indicates these naphthalene-oxacalix[m]arenes exhibit good fluorescence properties, which isattributed to the locally excited (LE) state emission, and electrochemical results show that the photoinduced electron transfer (PET) process occurs from the naphthalene substituent to the linked pyrimidine. Nanosecond transient absorption spectra, singlet oxygen quantum yields (ΦΔ4OA-N = 45.1%, ΦΔ6OA-N = 56.6%, and ΦΔ8OA-N = 65.7%) and theoretical calculations demonstrate that the torsion angle between the donor (naphthalene) and the acceptor (pyrimidine) promotes intersystem crossing (ISC), and the lifetime of the triplet state reaches ca. 8 ms. Interestingly, all three host molecules (4OA-N, 6OA-N, and 8OA-N) showed a high affinity for fullerene C60, and significant binding constants in the range of 4.10–6.68 × 104 M–1 were obtained by fluorescence titration; in contrast, previous reports indicated that the similar oxacalix[m]arene[n]pyrimidine scaffold could not efficiently complex with C60. In the frontier molecular orbital theory calculations of the supramolecular system of 4OA-N@C60, the HOMO is distributed on 4OA-N and the LUMO is localized on fullerene. The calculation results further demonstrated that there are strong interactions between the host and the fullerene guest, which is consistent with the result of the experiments. The characteristic photophysical properties of these novel naphthyl-decorated oxacalix[m]arene[n]pyrimidines broaden their application field, and the stable host–guest system with fullerene can be applied to supramolecular chemistry.

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 three-shell supramolecular complex enables the symmetry-mismatched chemo- and regioselective bis-functionalization of C60.

Molecular Russian dolls (matryoshkas) have proven useful for testing the limits of preparative supramolecular chemistry but applications of these architectures to problems in other fields are elusive. Here we report a three-shell, matryoshka-like complex-in which C60 sits inside a cycloparaphenylene nanohoop, which in turn is encapsulated inside a self-assembled nanocapsule-that can be used to address a long-standing challenge in fullerene chemistry, namely the selective formation of a particular fullerene bis-adduct. Spectroscopic evidence indicates that the ternary complex is sufficiently stable in solution for the two outer shells to affect the addition chemistry of the fullerene guest. When the complex is subjected to Bingel cyclopropanation conditions, the exclusive formation of a single trans-3 fullerene bis-adduct was observed in a reaction that typically yields more than a dozen products. The selectivity facilitated by this matryoshka-like approach appears to be a general phenomenon and could be useful for applications where regioisomerically pure C60 bis-adducts have been shown to have superior properties compared with isomer mixtures.

Cover Feature: Complexation of an Anthracene‐Triptycene Nanocage Host with Fullerene Guests through CH⋅⋅⋅π Contacts (ChemPlusChem 5/2021)

Cover Feature: Complexation of an Anthracene‐Triptycene Nanocage Host with Fullerene Guests through CH⋅⋅⋅π Contacts (ChemPlusChem 5/2021)

Complexation of an Anthracene‐Triptycene Nanocage Host with Fullerene Guests through CH⋅⋅⋅π Contacts

A bicyclic anthracene macrocycle containing two triptycene units at the bridgehead positions was synthesized by Ni-mediated coupling of the corresponding precursor as a cage-shaped aromatic hydrocarbon host. This cage host formed an inclusion complex with C60 or C70 guest in 1 : 1 ratio in solution. The association constants (Ka ) determined by the fluorescence titration method were 1.3×104 and 3.3×105 L mol -1 for the C60 and C70 complexes, respectively, at 298 K in toluene. DFT calculations revealed that the guest molecules were included in the middle of the cavity with several CH⋅⋅⋅π contacts. The strong affinity of the cage host for the fullerene guests and the high selectivity toward C70 are discussed on the basis of spectroscopic and structural data.