Fullerene Guests Research Articles

A perfect match: fullerene guests in star-shaped oligophenylenevinylene mesogens.

Star-shaped oligophenylenevinylene (OPV) mesogens are shape-persistent and possess formally large void space. A mesogen with three styrene repeating units packs densely in a columnar helical arrangement. Attachment of one fullerene through a short spacer results in an exceptional increase of the mesophase stability. X-ray scattering and modeling evidence a triple-helical arrangement in which the fullerene perfectly fills the void space between the arms of the star mesogen.

Solution and air stable host/guest architectures from a single layer covalent organic framework.

We show that the surface-supported two-dimensional covalent organic framework (COF) known as COF-1 can act as a host architecture for C60 fullerene molecules, predictably trapping the molecules under a range of conditions. The fullerenes occupy the COF-1 lattice at the solution/solid interface, and in dried films of the COF-1/fullerene network that can be synthesized through either drop-deposition of fullerene solution or by a dipstick-type synthesis in which the surface-supported COF-1 is briefly dipped into the fullerene solution.

Twofold fused concave hosts containing two phosphorus atoms: modules for the sandwich-type encapsulation of fullerenes in variable cavities.

The design and synthesis of extended concave host P2 by fusion of two concave phosphorus-containing units is reported. Co-crystallization of P2 and the fullerene guests C60 and C70 afforded the 2 : 1 host-guest complexes (P2)2 ⊃ C60 and (P2)2 ⊃ C70, in which the two concave surfaces of P2 encapsulate the convex surface of the fullerenes in a sandwich fashion. Interestingly, the orientation of the two P2 molecules with respect to each other was observed to be flexible, resulting in the formation of a variety of cavity shapes. MALDI-TOF mass, NMR, and UV-vis absorption spectra supported the formation of host-guest complexes between P2 and the fullerenes in solution. The affinity of P2, containing two phosphorus atoms, towards fullerenes was significantly enhanced relative to P1 with one phosphorus atom.

A novel photo-responsive azobenzene-containing nanoring host for fullerene-guest facile encapsulation and release.

Azobenzenes in particular have been proved to have a robust photo-response, in which their configuration can transform between the trans- and cis-form upon UV-visible irradiation. Accordingly, azobenzene-containing molecules are frequently applied in the design of the guests, involving so-called host-guest chemistry. In this paper, a novel photo-responsive nanoring host molecule ([4]AB) has been designed by introducing four azobenzene groups onto the ring, and interactions between the designed nanoring host and fullerenes C60 and C70 guests were investigated at both the M06-L/MIDI! as well as M06-2X/6-31G(d) level of theory. By analyzing the geometric characteristics and host-guest binding energies, it is revealed that the designed [4]AB with diameter ca. 13.4 Å is an ideal host molecule for the encapsulation of guests C60 and C70 fullerene. Meanwhile, inferred from UV-vis-NIR spectroscopy, the guest C60 and C70 could be facilely released from the cavity of the [4]AB via configuration transformation between trans- and cis-form of the host under 474 and 506 nm photo-irradiation, respectively. Frontier orbital features, weak interaction regions, infrared spectroscopy and (1)H NMR spectra have also been theoretically simulated. The present work would provide a new strategy for facile reversible encapsulation and release of fullerene guest by a novel nanoring host.

Ion-regulated allosteric binding of fullerenes (C60 and C70) by tetrathiafulvalene-calix[4]pyrroles.

The effect of ionic species on the binding of fullerenes (C60 and C70) by tetrathiafulvalene-calix[4]pyrrole (TTF-C4P) receptors and the nature of the resulting supramolecular complexes (TTF-C4P + fullerene + halide anion + tetraalkylammonium cation) was studied in the solid state through single crystal X-ray diffraction methods and in dichloromethane solution by means of continuous variation plots and UV-vis spectroscopic titrations. These analyses revealed a 1:1 stoichiometry between the anion-bound TTF-C4Ps and the complexed fullerenes. The latter guests are bound within the bowl-like cup of the C4P in a ball-and-socket binding mode. The interactions between the TTF-C4P receptors and the fullerene guests are highly influenced by both the nature of halide anions and their counter tetraalkylammonium cations. Three halides (F(-), Cl(-), and Br(-)) were studied. All three potentiate the binding of the two test fullerenes by inducing a conformational change from the 1,3-alternate to the cone conformer of the TTF-C4Ps, thus acting as positive heterotropic allosteric effectors. For a particular halide anion, the choice of tetraalkylammonium salts serves to modulate the strength of the TTF-C4P-fullerene host-guest binding interactions and, in conjunction with variations in the halide anion, can be exploited to alter the inherent selectivity of the host for a given fullerene. Differences in binding are reflected in the excited state optical properties. Overall, the present four-component system provides an illustration of how host-guest binding events involving appropriately designed artificial receptors can be fine-tuned via the addition of simple ionic species as allosteric modulators.

A Supramolecular Photosynthetic Model Made of a Multi-Porphyrinic Array Constructed Around a C60 Core and a C60-Imidazole Derivative

The photophysical properties of a supramolecular fullerene-porphyrin ensemble resulting from the self-assembly of a pyrrolidinofullerene-imidazole derivative (F1) with a multi-metalloporphyrin array constructed around a hexa-substituted fullerene core (F(ZnP)12 ) have been investigated. The fullerene hexa-adduct core of the host system does not play any active role in the cascade of photoinduced events of the supramolecular ensemble, indeed no intercomponent photoinduced processes could be observed in host F(ZnP)12 . In contrast, upon axial coordination with the mono-substituted fullerene guest F1, a quantitative quenching of the fluorescence signal of the metalloporphyrins was observed for the supramolecular complex [F(ZnP)12 (F1)n] both in polar and non polar solvents. In toluene, the supramolecular ensemble exhibits a charge transfer emission centered around 930 nm suggesting the occurrence of intramolecular face-to-face interactions of F1 with neighboring metalloporphyrin moieties within the self-assembled photoactive array. This mechanism is supported by the fact that a one order of magnitude increase in the binding constant was observed for the supramolecular complex [F(ZnP)12 (F1)n] when compared to a reference system lacking the pyrrolidino-fullerene unit. In benzonitrile, a long-lived charge separated state (τ = 0.3 μs) has been detected for the supramolecular adduct.ReferencesK. Yoosaf, J. Iehl, I. Nierengarten, M. Hmadeh, A.-M. Albrecht-Gary, J.-F. Nierengarten, N. Armaroli, Chem. Eur. J., 2014, in press

A Supramolecular Photosynthetic Model Made of a Multiporphyrinic Array Constructed around a C60 Core and a C60–Imidazole Derivative

The photophysical properties of a supramolecular fullerene-porphyrin ensemble resulting from the self-assembly of a pyrrolidinofullerene-imidazole derivative (F1) with a multimetalloporphyrin array constructed around a hexasubstituted fullerene core (F(ZnP)12) have been investigated. The fullerene hexa-adduct core of the host system does not play any active role in the cascade of photoinduced events of the supramolecular ensemble, indeed no intercomponent photoinduced processes could be observed in host F(ZnP)12. In contrast, upon axial coordination with the monosubstituted fullerene guest F1, a quantitative quenching of the fluorescence signal of the metalloporphyrins was observed for the supramolecular complex [F(ZnP)12(F1)n] both in polar and nonpolar solvents. In toluene, the supramolecular ensemble exhibits a charge transfer emission centered around nm, suggesting the occurrence of intramolecular face-to-face interactions of F1 with neighboring metalloporphyrin moieties within the self-assembled photoactive array. This mechanism is supported by the fact that a one order of magnitude increase in the binding constant was observed for the supramolecular complex [F(ZnP)12(F1)n] when compared with a reference system lacking the pyrrolidinofullerene unit. In benzonitrile, a long-lived charge-separated state (τ=0.3 μs) has been detected for the supramolecular adduct.

Composition- and Size-Controlled Cyclic Self-Assembly by Solvent- and C60-Responsive Self-Sorting

Synthesis, solvent-, and guest-controlled self-assembly, and self-sorting of new hydrogen-bonded chiral cavity receptors are reported. The design of the cavity is based on the cyclic self-aggregation of monomers containing the 4H-bonding ureidopyrimidinone motif fused with the bicylo[3.3.1]nonane framework. Selective formation of kinetically inert cyclic tetramers is observed in chloroform, while in toluene an equilibrium between tetrameric and pentameric forms exists. The high affinity of the tetrameric aggregates toward C60 and C70 is observed in aromatic solvents. The host-guest interaction of unconventional π-acidic supramolecular receptors for fullerenes is turned off and on by changing the solvent, whereas the selection of size and the very composition of the cavity aggregate is controlled by either the change of solvent or the addition of fullerene guest, making our systems a new type of self-sorting device.

Facile Catch and Release of Fullerenes Using a Photoresponsive Molecular Tube

A novel M2L2 molecular tube capable of binding fullerene C60 was synthesized from bispyridine ligands with embedded anthracene panels and Ag(I) hinges. Unlike previous molecular cages and capsules, this open-ended tubular host can accommodate a single molecule of various C60 derivatives with large substituents. The fullerene guest can then be released by using the ideal, noninvasive external stimulus, light.

Tridental molecular clip with corannulene pincers: is three better than two?

A molecular clip 3 (C87H54O6) with cyclotriveratrylene tether and three corannulene pincers was synthesized and tested for its affinity toward fullerenes. 1H NMR titration experiment in toluene-d8 suggests the formation of 1:1 fullerene@3 complexes and provides the association constants of 1500±50 and 1180±30M−1 for C60 and C70, respectively, lower than those previously reported for buckycatcher 2 complexes with fullerenes. In comparison with 2, 3 offers one more corannulene pincer able to bind with the fullerene guests, but the potentially higher gas-phase binding energies of its inclusion complexes are overridden by the more severe entropy and/or solvation penalties associated with the supramolecule formation in solution.

Cyclic metalloporphyrin dimers and tetramers: tunable shape-selective hosts for fullerenes

Covalently linked cyclic metalloporphyrin dimers and tetramers have been demonstrated to be good shape-selective hosts for fullerene guests. The fullerene affinities of these hosts can readily be tuned by modulating the covalent linkage and the metal ions in the porphyrin subunits. A rigid Zn(porphyrin) dimer with conjugated bis(alkynyl) linkers exhibits a high selectivity towards C(70) over C(60) in toluene (K(a,C70)/K(a,C60) = ~28). For the host structures examined, a synergistic combination of rigidity in the linker and electropositive Al ions gives rise to the strongest binding of C(70). In the case of a bisected Zn(porphyrin) tetramer, two well-defined cavities exist; however, due to their comparatively small size, only one C(60) can be accommodated. Studies of fullerene binding as a function of metal ion in a porphyrin divider suggest that the right combination of shape and steric match is essential to exploit both van der Waals and local-charge/induced-dipole interactions.

Proton‐Driven Switching Between Receptors for C60 and C70

Buckybinding: The selective binding of either C60 and C 70 in a mixture of the two fullerenes occurs by proton-induced, reversible, and controllable morphological switching between receptors for different fullerenes (see picture). Using hydrogen bonding as the exchange reaction, the response of the naphthalenediimide (NDI) building blocks to the presence of fullerene guests depends on the concentration of protons as a third component.

Enhanced binding strengths of acyclic porphyrin hosts with endohedral metallofullerenes

The complementary use of spectroscopy and electrochemistry shed light onto the supramolecular interactions of calixarene scaffold bearing bisporphyrins 1 and 2 as hosts with a series of fullerenes –C60, Sc3N@C80, and Lu3N@C80 – as guest molecules. Importantly, the present work shows a noticeable variation in binding strength when C60 or endohedral fullerene guests are included into the bisporphyrins hosts. These sizeable differences could be clarified by computational models of the host–guest complexes, on the one hand, and a systematic investigation of the electron transfer chemistry, on the other hand. Detailed studies document an oxidative charge transfer (i.e., electron transfer from the bisporphyrin to the fullerene) for the C60 inclusion complexes, while a reductive charge transfer (i.e., electron transfer from the fullerene to porphyrin) is operative in the endohedral metallofullerene host–guest complexes.

Structures and properties of hemiquinone-substituted oxoporphyrinogens

The structure and physical properties of a series of N-substituted, hemiquinone-substituted oxoporphyrinogens is presented and discussed. Structures of the compounds are dictated by the nature of the substituent, with the substitution pattern being in turn dictated by regioselectivity of N-alkylation. X-ray crystallography and other aggregation properties of the compounds are discussed. Redox reactions are also strongly influenced by N-substitution and substituent identity. Also presented are properties related to guest binding and photophysical properties of oligochromophoric host-guest complexes, involving oxoporphyrinogen, N-substituted with porphyrins and appropriately substituted fullerene guest electron acceptors.

Binding studies of tetrathiafulvalene-calix[4]pyrroles with electron-deficient guests

The neutral meso-octamethylporphyrinogen derivative, tetraTTF-calix[4]pyrrole 1 (TTF=tetrathiafulvalene), acts as a multi-faceted receptor in that it interacts with an assortment of different guests in different ways. The conformation of receptor 1 can be reversibly switched between the 1,3-alternate conformation (i.e., 1, Fig. 1) and the cone conformation (i.e., 1·Cl −, Fig. 2) by the repetitive addition of chloride and sodium ions. In this paper, the results of detailed and systematic complexation studies involving both 1 and its chloride-bound complex, 1·Cl −, with a variety of guests are described. Receptor 1 binds quasi-planar nitroaromatic guests in its 1,3-alternate conformation, while release of these guests takes place upon addition of chloride anions. On the other hand, spherical fullerene guests are strongly bound by 1·Cl −. Finally, it was found that a bidentate guest, consisting of a quasi-planar 2,5,7-trinitro-9-dicyanomethylenefluorene moiety tethered to a spherical C 60 fullerene, could be recognized by receptor 1 in either its 1,3-alternate or its chloride-bound cone conformation, albeit through very different binding modes.

Supramolecular Nanostructuring of Silver Surfaces via Self‐Assembly of [60]Fullerene and Porphyrin Modules

AbstractRecent achievements in our laboratory toward the “bottom‐up” fabrication of addressable multicomponent molecular entities obtained by self‐assembly of C60 and porphyrins on Ag(100) and Ag(111) surfaces are described. Scanning tunneling microscopy (STM) studies on ad‐layers constituting monomeric and triply linked porphyrin modules showed that the molecules self‐organize into ordered supramolecular assemblies, the ordering of which is controlled by the porphyrin chemical structure, the metal substrate, and the surface coverage. Specifically, the successful preparation of unprecedented two‐dimensional porphyrin‐based assemblies featuring regular pores on Ag(111) surfaces has been achieved. Subsequent co‐deposition of C60 molecules on top of the porphyrin monolayers results in selective self‐organization into ordered molecular hybrid bilayers, the organization of which is driven by both fullerene coverage and porphyrin structure. In all‐ordered fullerene–porphyrin assemblies, the C60 guests organize, unusually, into long chains and/or two‐dimensional arrays. Furthermore, sublimation of C60 on top of the porous porphyrin network reveals the selective long‐range inclusion of the fullerene guests within the hosting cavities. The observed mode of the C60 self‐assembly originates from a delicate equilibrium between substrate–molecule and molecule–molecule interactions involving charge‐transfer processes and conformational reorganizations as a consequence of the structural adaptation of the fullerene–porphyrin bilayer.

Calix[4]arene-Linked Bisporphyrin Hosts for Fullerenes: Binding Strength, Solvation Effects, and Porphyrin−Fullerene Charge Transfer Bands

A calix[4]arene scaffolding has been used to construct bisporphyrin ("jaws" porphyrin) hosts for supramolecular binding of fullerene guests. Fullerene affinities were optimized by varying the nature of the covalent linkage of the porphyrins to the calixarenes. Binding constants for C60 and C70 in toluene were explored as a function of substituents at the periphery of the porphyrin, and 3,5-di-tert-butylphenyl groups gave rise to the highest fullerene affinities (26,000 M(-1) for C60). The origin of this high fullerene affinity has been traced to differential solvation effects rather than to electronic effects. Studies of binding constants as a function of solvent (toluene < benzonitrile < dichloromethane < cyclohexane) correlate inversely with fullerene solubility, indicating that desolvation of the fullerene is a major factor determining the magnitude of binding constants. The energetics of fullerene binding have been determined in terms of DelatH and DeltaS and are consistent with an enthalpy-driven, solvation-dependent process. A direct relationship between supramolecular binding of a fullerene guest to a bisporphyrin host and the appearance of a broad NIR absorption band have been established. The energy of this band moves in a predictable manner as a function of the electronic structure of the porphyrin, thereby establishing its origin in porphyrin-to-fullerene charge transfer.

Ordered inclusion of endohedral fullerenes N@C 60 and P@C 60 in a crystalline matrix

The organic inclusion compound 2,4,6-tris-(4-bromophenoxy)-1,3,5-triazine was used to create an ordered arrangement of the endohedral fullerenes N@C 60 and P@C 60 in a crystalline host matrix. Two different host–guest structures were investigated by X-ray diffraction and electron paramagnetic resonance. In one of these, an axial deformation of the fullerene guests leads to a sizeable zero-field splitting of the quartet ground state of the encapsulated atoms. The small size of the zero-field strain leads to well-separated lines for all transitions, opening the possibility of transition selective pulses for future quantum computing experiments in these multi-level systems.

Nanosized Polymetallic Resorcinarene-Based Host Assemblies that Strongly Bind Fullerenes

Polymetallic nanodimensional assemblies have been prepared via metal directed assembly of dithiocarbamate functionalized cavitand structural frameworks with late transition metals (Ni, Pd, Cu, Au, Zn, and Cd). The coordination geometry about the metal centers is shown to dictate the architecture adopted. X-ray crystallographic studies confirm that square planar coordination geometries result in "cagelike" octanuclear complexes, whereas square-based pyramidal metal geometries favor hexanuclear "molecular loop" structures. Both classes of complex are sterically and electronically complementary to the fullerenes (C(60) and C(70)). The strong binding of these guests occurred via favorable interactions with the sulfur atoms of multiple dithiocarbamate moieties of the hosts. In the case of the tetrameric copper(II) complexes, the lability of the copper(II)-dithiocarbamate bond enabled the fullerene guests to be encapsulated in the electron-rich cavity of the host, over time. The examination of the binding of fullerenes has been undertaken using spectroscopic and electrochemical methods, electrospray mass spectrometry, and molecular modeling.

Cover Picture: A Two‐Dimensional Porphyrin‐Based Porous Network Featuring Communicating Cavities for the Templated Complexation of Fullerenes (Adv. Mater. 3/2006)

AbstractA 2D porous network has been realized by self‐assembly of porphyrin modules on a silver surface, as reported by Diederich and co‐workers on p. 275. The so‐formed pores are able to host single fullerene molecules and mediate long‐range interactions between such carbon guests, resulting in the formation of large supramolecular chains and islands. The cover shows a scanning tunnelling microscopy image of several single C60 molecules (large green protrusions) hosted in the 2D porous network. As indicated by the molecular model, each pore is formed by the symmetric arrangement of three porphyrin molecules and the fullerene guest is located exactly in the center of the cavity.