Macrocyclic Hosts for Fullerenes: Extreme Changes in Binding Abilities with Small Structural Variations

Conformation Regulation of Trisresorcinarene Directed by Cavity Solvation

This compound is a synthetic macrocycle comprising three pivaloyl-protected resorcinarene units connected by six pentylene chains. We conducted a conformational study using 1H-NMR, X-ray diffraction (XRD), and computational analyses. The macrocycle adopts two conformers, one open, the other closed. The ratio of the open to closed forms depended on the solvent used. Only the open form existed in [D8]toluene, both forms coexisted in [D6]benzene, and the closed form was the major conformer in [D1]chloroform. The benzene-solvated open form observed in the solid state suggests that cavity solvation by solvent molecules directs the open form. The open form was the major or only conformer in [D10]o- and [D10]m-xylene and [D12]mesitylene, whereas the closed form was the major conformer in [D6]acetone. The open and closed forms were equally populated in [D10]p-xylene, suggesting that the size, shape, and dimensions of the solvent molecules most likely influenced the conformation of the protected trisresocinarene.

Recent update on the electroactive oligopyrrolic macrocyclic hosts with a Bucky-ball heart

Supramolecular chemistry is a multidisciplinary research area mostly associated with the investigation of host-guest interactions within intricate three-dimensional (3D) molecular architectures held together reversibly by various non-covalent interactions. Continuous efforts to develop such kinds of complex host-guest systems with designer oligopyrrolic macrocyclic receptors are a rapidly growing research domain, which is deeply involved in applied supramolecular chemistry research. These host-guest supramolecular complexes can be constructed by combining suitable electron-rich oligopyrrolic donors (as a host) with complementary electron-poor guests (as acceptors), held together by the ionic force of attraction triggered by intermolecular charge/electron transfer (CT/ET) transitions. Some of these resulting CT/ET ensembles are potential candidates for the construction of efficient optoelectronic materials, optical sensors, molecular switches, etc. In this Feature Article we aim to focus on these supramolecular ensembles composed by size and shape complementary electroactive oligopyrrolic molecular containers, which are suitable for spherical guest (e.g., buckminsterfullerene) complexation. We also provide a "state-of-the-art" overview on plausible applications of these particular host-guest systems. Our aim is to cover only specific electron-rich tetrathiafulvalene (TTF)-based oligopyrrolic receptors, e.g., TTF-calix[4]pyrroles, TTF-cryptands, TTF-porphyrins and exTTF-porphyrin-based molecular motifs reported to date, along with a brief outlining of their "functional behaviour" in materials chemistry research.

Theoretical understanding of stability of mechanically interlocked carbon nanotubes and their precursors

Dispersion-corrected DFT calculations were performed on (a,a) nanotubes (a = 5-10) attached by a U-shaped functional group consisting of p-xylene-linked double 9,10-di(1,3-dithiol-2-ylidene)-9,10-dihydro anthracene terminated by C_nH_2n chains (n = 6, 8, and 9), and their ring-closing macrocycles containing tubes. The reactant precursors and macrocycles are denoted by UP-n-(a,a) and (a,a)@Cycle-n, respectively. We found that UP-n-(a,a) are energetically preferable relative to the dissociation limit toward a U-shaped functional group (UP-n) and a tube (initial state) due to the attractive CH-π and π-π interactions. The attractive interactions are enhanced by increasing the tube diameters and C_nH_2n chain lengths because UP-n structures can be easily adjusted to interact with the tubes. The stability of (a,a)@Cycle-n and related (a,b)@Cycle-n is sensitive to tube diameters due to the restriction of ring structures. When diameter differences between a Cycle-n and a tube (D-d) are larger than 5 Å, (a,a)@Cycle-n plus C₂H₄ are energetically preferable relative to the initial state. However, the (a,a)@Cycle-n plus C₂H₄ byproduct is always energetically unstable relative to UP-n-(a,a). The DFT calculations found that the energy differences were low at D-d values ranging from 7 to 8 Å, explaining the tube-diameter-selective formation of the mechanically-interlocked tubes, observed experimentally.

Supramolecular Recognition within a Nanosized "Buckytrap" That Exhibits Substantial Photoconductivity

We report here a nanosized "buckytrap", 1, constructed from two bis-zinc(II) expanded-TTF (exTTF) porphyrin subunits. Two forms, 1a and 1b, differing in the axial ligands, H₂O vs tetrahydrofuran (THF), were isolated and characterized. Discrete host-guest inclusion complexes are formed upon treatment with fullerenes as inferred from a single-crystal X-ray structural analyses of 1a with C₇₀. The fullerene is found to be encapsulated within the inner pseudohexagonal cavity of 1a. In contrast, the corresponding free-base derivative (2) was found to form infinite ball-and-socket type supramolecular organic frameworks (3D-SOFs) with fullerenes, (2•C₆₀)_n or (2•C₇₀)_n. This difference is ascribed to the fact that in 1a and 1b the axial positions are blocked by a H₂O or THF ligand. Emission spectroscopic studies supported a 1:1 host-guest binding stoichiometry, allowing association constants of (2.0 ± 0.5) × 10⁴ M^-1 and (4.3 ± 0.9) × 10⁴ M^-1 to be calculated for C₆₀ and C₇₀, respectively. Flash-photolysis time-resolved microwave conductivity (FP-TRMC) studies of solid films of the Zn-complex 1a revealed that the intrinsic charge carrier transport, i.e., pseudo-photoconductivity (ϕ∑μ), increases upon fullerene inclusion (e.g., ϕ∑μ = 1.53 × 10^-4 cm² V^-1 s^-1 for C₆₀⊂(1a)₂ and ϕ∑μ = 1.45 × 10^-4 cm² V^-1 s^-1 for C₇₀⊂(1a)₂ vs ϕ∑μ = 2.49 × 10^-5 cm² V^-1 s^-1 for 1a) at 298 K. These findings provide support for the notion that controlling the nature of self-assembly supramolecular constructs formed from exTTF-porphyrin dimers through metalation or choice of fullerene can be used to regulate key functional features, including photoconductivity.

Single-Walled Carbon Nanotubes Encapsulated within Metallacycles

Mechanically interlocked derivatives of carbon nanotubes (MINTs) are interesting nanotube products since they show high stability without altering the carbon nanotube structure. So far, MINTs have been synthesized using ring-closing metathesis, disulfide exchange reaction, H-bonding or direct threading with macrocycles. Here, we describe the encapsulation of single-walled carbon nanotubes within a palladium-based metallosquare. The formation of MINTs was confirmed by a variety of techniques, including high-resolution transmission electron microscopy. We find the making of these MINTs is remarkably sensitive to structural variations of the metallo-assemblies. When a metallosquare with a cavity of appropriate shape and size is used, the formation of the MINT proceeds successfully by both templated clipping and direct threading. Our studies also show indications on how supramolecular coordination complexes can help expand the potential applications of MINTs.

Stereoelectronically-induced allosteric binding: shape complementarity promotes positive cooperativity in fullerene/buckybowl complexes

A novel 2 : 1 host-guest complex forms between 8-tert-butyl-6b²-azapenta-benzo[bc,ef,hi,kl,no]corannulene (1) and C₆₀ with positive cooperativity (α = 2.56) and high affinity (K₁ × K₂ = 2.8 × 10⁶ M^-2) at 25 °C. The C₆₀ undergoes increasing shape complementarity toward 1 throughout the binding process.

Gram-scale synthesis of a covalent nanocage that preserves the redox properties of encapsulated fullerenes

Discrete nanocages provide a way to solubilize, separate, and tune the properties of fullerenes, but these 3D receptors cannot usually be synthesized easily from inexpensive starting materials, limiting their utility. Herein, we describe the first fullerene-binding nanocage (Cage⁴⁺) that can be made efficiently on a gram scale. Cage⁴⁺ was prepared in up to 57% yield by the formation of pyridinium linkages between complemantary porphyrin components that are themselves readily accessible. Cage⁴⁺ binds C₆₀ and C₇₀ with large association constants (>10⁸ M⁻¹), thereby solubilizing these fullerenes in polar solvents. Fullerene association and redox-properties were subsequently investigated across multiple charge states of the host-guest complexes. Remarkably, neutral and singly reduced fullerenes bind with similar strengths, leaving their 0/1⁻ redox couples minimally perturbed and fully reversible, whereas other hosts substantially alter the redox properties of fullerenes. Thus, C₆₀@Cage⁴⁺ and C₇₀@Cage⁴⁺ may be useful as solubilized fullerene derivatives that preserve the inherent electron-accepting and electron-transfer capabilities of the fullerenes. Fulleride dianions were also found to bind strongly in Cage⁴⁺, while further reduction is centered on the host, leading to lowered association of the fulleride guest in the case of C₆₀²⁻.

This report describes the first gram-scale synthesis of a nanocage that can host fullerenes (C₆₀ and C₇₀). The redox properties of the fullerenes are preserved in this host, enabling characterization of complexes with fulleride anions and dianions.

Heterospin frustration in a metal-fullerene-bonded semiconductive antiferromagnet

Lithium-ion-encapsulated fullerenes (Li⁺@C₆₀) are 3D superatoms with rich oxidative states. Here we show a conductive and magnetically frustrated metal–fullerene-bonded framework {[Cu₄(Li@C₆₀)(L)(py)₄](NTf₂)(hexane)}_n (1) (L = 1,2,4,5-tetrakis(methanesulfonamido)benzene, py = pyridine, NTf₂⁻ = bis(trifluoromethane)sulfonamide anion) prepared from redox-active dinuclear metal complex Cu₂(L)(py)₄ and lithium-ion-encapsulated fullerene salt (Li⁺@C₆₀)(NTf₂⁻). Electron donor Cu₂(L)(py)₂ bonds to acceptor Li⁺@C₆₀ via eight Cu‒C bonds. Cu–C bond formation stems from spontaneous charge transfer (CT) between Cu₂(L)(py)₄ and (Li⁺@C₆₀)(NTf₂⁻) by removing the two-terminal py molecules, yielding triplet ground state [Cu₂(L)(py)₂]⁺(Li⁺@C₆₀^•−), evidenced by absorption and electron paramagnetic resonance (EPR) spectra, magnetic properties and quantum chemical calculations. Moreover, Li⁺@C₆₀^•− radicals (S = ½) and Cu²⁺ ions (S = ½) interact antiferromagnetically in triangular spin lattices in the absence of long-range magnetic ordering to 1.8 K. The low-temperature heat capacity indicated that compound 1 is a potential candidate for an S = ½ quantum spin liquid (QSL).

Conductive and magnetically frustrated solids may enable the development of high-performance molecule-based spintronic devices. Here the authors report a conductive and magnetically frustrated metal–fullerene-bonded framework prepared from a redox-active dinuclear copper complex and lithium ion-encapsulated fullerenes.

Breathing Room: Restoring Free Rotation in a Schiff-Base Macrocycle through Endoperoxide Formation

Macrocyclization is a popular method for preparing hosts, but it can have unintended effects, like limiting molecular free rotation to yield mixtures of inseparable isomers. We report a [3 + 3] Schiff-base macrocycle (1) with anthracene bridges. Restricted rotation about the phenyl-anthracene bonds leads 1 to exist as a mixture of conformations (1^C_s and 1^C_3v). Macrocycle 1 was photooxidized to tris(endoperoxide) adduct 4, alleviating restricted rotation. These results were supported by spectroscopic, structural, and computational analyses.

Reversible pH-Controlled Catenation of a Benzobisimidazole-Based Tetranuclear Rectangle

The development of methodologies to control on demand and reversibly supramolecular transformations from self-assembled metalla-structures requires the rational design of architectures able to answer to an applied stimulus. While solvent or concentration changes, light exposure or addition of a chemical have been largely explored to provide these transformations, the case of pH sensitive materials is less described. Herein, we report the first example of a pH-triggered dissociation of a coordination-driven self-assembled interlocked molecular link. It incorporates a pH sensitive benzobisimidazole-based ligand that can be selectively protonated on its bisimidazole moieties. This generates intermolecular electrostatic repulsions that reduces drastically the stability of the interlocked structure, leading to its dissociation without any sign of protonation of the pyridine moieties involved in the coordination bonds. Importantly, the dissociation process is reversible through addition of a base.

Structural Tuning of Curved TTFAQ-AQ as a Redox-Active Supramolecular Partner for C70 Fullerene

A series of saddle-shaped donor-acceptor π-systems, termed TTFAQ-AQs, were designed and synthesized. The molecular structures of TTFAQ-AQs feature a π-fused framework containing an anthraquinodimethane extended tetrathiafulvalene (TTFAQ) as the donor and an anthraquinone (AQ) unit as the acceptor. As such, TTFAQ-AQs show enhanced intramolecular charge-transfer properties, which result in amphoteric redox behavior and narrow electronic energy band gaps. Detailed structural and electronic properties were investigated by UV-vis absorption, cyclic voltammetric, and single-crystal X-ray diffraction (SCXRD) analyses. The supramolecular interactions of TTFAQ-AQs with C₆₀ and C₇₀ fullerenes were examined in both the solution and solid phases. Our results showed that the benzoannulated TTFAQ-AQ derivative favors interaction with C₇₀ fullerene through complementary concave-convex interactions. Detailed energetics involved in the TTFAQ-AQ/C₇₀ interactions were assessed by means of density functional theory (DFT) calculations.

ON/OFF metal-triggered molecular tweezers for fullerene recognition

Herein, we report molecular tweezers for fullerene recognition based on 2,2'-bipyridine-bearing corannulene motifs. The syn or anti confirmation can be selected simply by Cu(I) coordination/decoordination, thus controlling the fullerene recognition capability of the system on demand and leading to the formation of effective metal-triggered ON/OFF molecular tweezers.

A supramolecular polymeric heterojunction composed of an all-carbon conjugated polymer and fullerenes

Herein, we design and synthesize a novel all-carbon supramolecular polymer host (SPh) containing conjugated macrocycles interconnected by a linear poly(para-phenylene) backbone. Applying the supramolecular host and fullerene C60 as the guest, we successfully construct a supramolecular polymeric heterojunction (SPh⊃C60). This carbon structure offers a means to explore the convex-concave π-π interactions between SPh and C60. The produced SPh was characterized by gel permeation chromatography, mass spectrometry, FTIR, Raman spectroscopy, and other spectroscopies. The polymeric segment can be directly viewed using a scanning tunneling microscope. Femtosecond transient absorption and fluorescence up-conversion measurements revealed femtosecond (≪300 fs) electron transfer from photoexcited SPh to C60, followed by nanosecond charge recombination to produce the C60 triplet excited state. The potential applications of SPh⊃C60 in electron- and hole-transport devices were also investigated, revealing that C60 incorporation enhances the charge transport properties of SPh. These results expand the scope of the synthesis and application of supramolecular polymeric heterojunctions.

Figure-eight arylene ethynylene macrocycles: facile synthesis and specific binding behavior toward Hg2+

Two figure-eight arylene ethynylene macrocycles (AEMs) were synthesized from non-helical precursors and the figure-eight shape was clearly imaged by STM.

One-pot synthesis of conjugated triphenylamine macrocycles and their complexation with fullerenes

Triphenylamine derivates have been utilized as building blocks in hole-transporting materials. Herein, we describe the synthesis of three octyl-derived conjugated triphenylamine macrocycles with different sizes, and a 4-(2-ethylhexyloxy)-substituted cyclic triphenylamine hexamer using a palladium-catalyzed C–N coupling reaction. These conjugated triphenylamine macrocycles not only have interesting structures, but also are capable of complexing with C₆₀, C₇₀ and PC₆₁BM. Their binding stoichiometries with fullerenes were all determined to be 1 : 1 by an emission titration method. The association constants of these complexes were measured to be in the range of 0.115–1.53 × 10⁵ M⁻¹ depending on the cavity size of the triphenylamine macrocycles and the volume of the fullerenes. The space-charge-limited current properties of the complexes were further investigated using the fabricated ITO/PEDOT:PSS/active layer/Au devices.

Cyclic triphenylamine (TPA) oligomers synthesized by C–N coupling were found to be capable of complexing with fullerenes, and the applications in optoelectronic devices were investigated by using the fabricated ITO/PEDOT:PSS/active layer/Au devices.

Comparing the self-assembly processes of two redox-active exTTF-based regioisomer ligands

A new exTTF-based ligand was synthesized and its coordination-driven self-assembly behavior with a square planar palladium complex was compared with a previously described regioisomer.

Dynamic Covalent Formation of Concave Disulfide Macrocycles Mechanically Interlocked with Single-Walled Carbon Nanotubes

The formation of discrete macrocycles wrapped around single-walled carbon nanotubes (SWCNTs) has recently emerged as an appealing strategy to functionalize these carbon nanomaterials and modify their properties. Here, we demonstrate that the reversible disulfide exchange reaction, which proceeds under mild conditions, can install relatively large amounts of mechanically interlocked disulfide macrocycles on the one-dimensional nanotubes. Size-selective functionalization of a mixture of SWCNTs of different diameters were observed, presumably arising from error correction and the presence of relatively rigid, curved π-systems in the key building blocks. A combination of UV/Vis/NIR, Raman, photoluminescence excitation, and transient absorption spectroscopy indicated that the small (6,4)-SWCNTs were predominantly functionalized by the small macrocycles 1₂ , whereas the larger (6,5)-SWCNTs were an ideal match for the larger macrocycles 2₂ . This size selectivity, which was rationalized computationally, could prove useful for the purification of nanotube mixtures, since the disulfide macrocycles can be removed quantitatively under mild reductive conditions.

Theoretical Prediction on a Novel Reduction-Responsive Nanoring Having a Disulfide Group for Facile Encapsulation and Release of Fullerenes C60 and C70

In this work, a novel reduction-responsive disulfide bond-containing cycloparaphenylene nanoring molecule (DSCPP) with a pyriform shape has been designed. In addition, the interactions between the designed nanoring (host) and fullerenes C₆₀ and C₇₀ (guests) were investigated theoretically at the M06-2X/6-31G(d,p) and M06-L/MIDI! levels of theory. By analyzing geometric characteristics and host-guest binding energies, it is revealed that the designed DSCPP is an ideal host molecule of guests C₆₀ and C₇₀. DSCPP presents excellent elastic deformation during the encapsulation of C₆₀ and C₇₀. The high binding energies suggest that both DSCPP⊃C₆₀ and DSCPP⊃C₇₀ (∼92 and 118 kJ·mol^-1 at the M06-2X/6-31G(d,p) level of theory) are stable host-guest complexes, and the guest C₇₀ is more strongly encapsulated than C₆₀ in the gas phase. The thermodynamic information indicates that the formation of the two host-guest complexes is thermodynamically spontaneous. In addition, the frontier molecular orbital (FMO) features and intermolecular weak interaction region between DSCPP and fullerenes gusts are discussed to further understand the structures and properties of the DSCPP⊃fullerene systems. Finally, the ring-opening mechanism of the DSCPP under reduction conditions is investigated.

Mechanically Interlocked Carbon Nanotubes as a Stable Electrocatalytic Platform for Oxygen Reduction

Mechanically interlocking redox-active anthraquinone onto single-walled carbon nanotubes (AQ-MINT) gives a new and advanced example of a noncovalent architecture for an electrochemical platform. Electrochemical studies of AQ-MINT as an electrode reveal enhanced electrochemical stability in both aqueous and organic solvents compared to physisorbed AQ-based electrodes. While maintaining the electrochemical properties of the parent anthraquinone molecules, we observe a stable oxygen reduction reaction to hydrogen peroxide (H₂O₂). Using such AQ-MINT electrodes, 7 and 2 μmol of H₂O₂ are produced over 8 h under basic and neutral conditions, while the control system of SWCNTs produces 2.2 and 0.5 μmol, respectively. These results reveal the potential of this rotaxane-type immobilization approach for heterogenized electrocatalysis.

Metalla-Assembled Electron-Rich Tweezers: Redox-Controlled Guest Release Through Supramolecular Dimerization

Developing methodologies for on-demand control of the release of a molecular guest requires the rational design of stimuli-responsive hosts with functional cavities. While a substantial number of responsive metallacages have already been described, the case of coordination-tweezers has been less explored. Herein, we report the first example of a redox-triggered guest release from a metalla-assembled tweezer. This tweezer incorporates two redox-active panels constructed from the electron-rich 9-(1,3-dithiol-2-ylidene)fluorene unit that are facing each other. It dimerizes spontaneously in solution and the resulting interpenetrated supramolecular structure can dissociate in the presence of an electron-poor planar unit, forming a 1:1 host-guest complex. This complex dissociates upon tweezer oxidation/dimerization, offering an original redox-triggered molecular delivery pathway.

A sulfur-containing hetero-octulene: synthesis, host–guest properties, and transistor applications

A heterocycloarene derivative (S-Octulene) possessing two sulfur atoms was conveniently synthesized through Bi(OTf)₃-catalyzed cyclization from a macrocyclic tetramethoxyethenylated precursor.

Tuning the structure and the properties of dithiafulvene metalla-assembled tweezers

An electroactive M₂L₂ metalla-macrocycle constructed through coordination driven self-assembly dimerizes upon oxidation and binds an electro-deficient substrate with a high association constant.

Photoconductive Curved-Nanographene/Fullerene Supramolecular Heterojunctions

This study presents synthesis and characterizations of two novel curved nanographenes that strongly bind with fullerene C₆₀ to form photoconductive heterojunctions. Films of the self-assembled curved nanographene/fullerene complexes, which served as the photoconductive layer, generated a significant photocurrent under light irradiation. Gram-scale quantities of these curved nanographenes (TCR and HCR) as the "crown" sidewalls can be incorporated into a carbon nanoring to form molecular crowns, and the molecular structure of C₆₀ @TCR is determined by single-crystal X-ray diffraction. The UV/Vis absorption and emission spectra, and theoretical studies revealed their unique structural features and photophysical properties. Time-resolved spectroscopic results clearly suggest fast photoinduced electron transfer process in the supramolecular heterojunctions.

Conformational Analysis of the Supramolecular Complexation of Diaryl-Substituted Tetrathiafulvalene Vinylogues with Fullerenes

Tetrathiafulvalene vinylogues (TTFVs) functionalized with diaryl substituents (aryl = 1-napthyl, 9-anthryl, and 1-pyrenyl) via click chemistry have been previously synthesized and studied as tweezer-type receptors for binding with C60 and C70 fullerenes. In particular, dianthryl-TTFV exhibits unique selectivity for C70 fullerene, giving rise to effective fluorescence turn-on sensing of C70 in the presence of a large excess of C60 fullerene. This observation indicated that dianthryl-TTFV has a preferential binding affinity for C70 over C60 fullerene, but the reason for such selectivity is unclear. Aiming at addressing this issue, we herein investigated the relative conformational stability of diaryl-substituted TTFVs in complexation with C70 and C60 fullerenes. The dispersion-corrected density functional theory approximation (B3LYP-D3) was employed in our computational analysis to determine binding energies and electronic properties of these supramolecular complexes. It was found that the highest binding energies (and the lowest relative conformational energies) are in pairings when fullerenes are placed around the central TTFV moieties (such as the triazole rings). The results of electronic properties show that the dianthryl-TTFV and dipyrenyl-TTFV conformers have lower highest occupied molecular orbital-lowest unoccupied molecular orbital gaps relative to the ones obtained for dinaphthyl-TTFV, indicating that dianthryl-TTFV, and to some extend dipyrenyl-TTFV, could be good candidates for chemical sensing of fullerenes with fluorescence spectroscopy. We also investigated the effect of the solvent on the interactions of the diaryl-TTFVs with fullerenes using the polarizable continuum model. In general, the presence of a solvent decreases the diaryl-TTFV/fullerene binding energies, presumably because of the interactions of the solvent with individual fullerenes and diaryl-TTFVs.

Understanding the affinity of bis-exTTF macrocyclic receptors towards fullerene recognition

Embracing [60]fullerene: Quantification of the C₆₀ affinity with a new series of exTTF macrocycles allows understanding the driving forces governing the supramolecular recognition upon increasing the alkyl ether chain size. Counterintuitively, an outside-ring complexation is found as the preferred arrangement over the expected inside-ring disposition.

A Polyaromatic Nano-nest for Hosting Fullerenes C60 and C70

A "Janus" type of hexa- cata-hexabenzocoronene with three triptyceno subunits fused symmetrically on the periphery of coronene has been synthesized using a covalent self-assembly strategy. The triptyceno subunits form a nanosized nest on one side of the aromatic plane with space-matching fullerenes such as C₆₀ and C₇₀ to afford shape-complementary supramolecular complexes. The formation of the complexes in solution was confirmed by ¹H NMR and fluorescence titration. Four complexes with C₆₀ or C₇₀ were obtained and studied by single-crystal X-ray diffraction analysis. In the crystal structure, the host shows a proper tunability to adjust its conformation in accordance with the shape of the guest. The different stoichiometric ratios and various stacking patterns of the complexes suggest the diversity of this nonplanar polyaromatic host in complexation with fullerenes.

Functionalised tetrathiafulvalene- (TTF-) macrocycles: recent trends in applied supramolecular chemistry

Tetrathiafulvalene- (TTF-) based macrocyclic systems, cages and supramolecularly self-assembled 3D constructs have been extensively explored as functional materials for sensing and switching applications.

Donor-Acceptor Conjugated Macrocycles: Synthesis and Host-Guest Coassembly with Fullerene toward Photovoltaic Application

Electron-rich (donor) and electron-deficient (acceptor) units to construct donor-acceptor (D-A) conjugated macrocycles were investigated to elucidate their interactions with electron-deficient fullerene. Triphenylamine and 4,7-bisthienyl-2,1,3-benzothiadiazole were alternately linked through acetylene, as the donor and acceptor units, respectively, for pentagonal 3B2A and hexagonal 4B2A macrocycles. As detected by scanning tunneling microscopy, both D-A macrocycles were found to form an interesting concentration-controlled nanoporous monolayer on highly oriented pyrolytic graphite, which could effectively capture fullerene. Significantly, the fullerene filling was cavity-size-dependent with only one C₇₀ or PC₇₁BM molecule accommodated by 3B2A, while two were accommodated by 4B2A. Density functional theory calculations were also utilized to gain insight into the host-guest systems and indicted that the S···π contact is responsible for stabilizing these host-guest systems. Owing to the ellipsoidal shape of C₇₀, C₇₀ molecules are standing or lying in molecular cavities depending on the energy optimization. For the 3B2A/PC₇₁BM blended film, PC₇₁BM was intercalated into the cavity formed by the macrocycle 3B2A and provided excellent power conversion efficiency despite the broad band gap (2.1 eV) of 3B2A. This study of D-A macrocycles incorporating fullerene provides insights into the interaction mechanism and electronic structure in the host-guest complexes. More importantly, this is a representative example using D-A macrocycles as a donor to match with the spherical fullerene acceptor for photovoltaic applications, which offer a good approach to achieve molecular scale p-n junctions for substantially enhanced efficiencies of organic solar cells through replacing linear polymer donors by cyclic conjugated oligomers.

A bis-corannulene based molecular tweezer with highly sensitive and selective complexation of C70 over C60

A corannulene-based tweezer-like receptor was conveniently synthesized, which showed highly sensitive and selective complexation of C₇₀ over C₆₀.