Enhancing solution-phase supramolecular interactions between monomeric porphyrins and [60]fullerene by simple chemical modification

The supramolecular interactions of N-methylporphyrin and iridium porphyrin with C₆₀ in toluene solution were investigated using NMR spectroscopy and absorption spectroscopy. Our results demonstrate that both the N-methylation and iridium metalation of porphyrin are effective means to enhance the binding affinity to C₆₀, resulting in 1:1 complexation for N-methylporphyrin/C₆₀ and 2:1 complexation for iridium porphyrin/C₆₀.     

Multiple hydrogen-bond-induced supramolecular nanostructure from a pincer-like molecule and a [60]fullerene derivative

A new supramolecular self-assembled system between a perylene bisimide bearing diaminopyridine-substituted isophthalamide groups (PP) and a [60]fullerene containing barbituric acid moiety (C₆₀bar) through a complementary six-point hydrogen-bonding interaction was constructed. The formation of hydrogen bonding was confirmed by ¹H NMR spectra studies in CDCl₃. Fluorescence quenching experiments indicated that the fluorescence of PP was greatly quenched by the hydrogen-bonded C₆₀bar (K_sv=2.71×10⁴ M⁻¹). A steady and rapid cathodic 0.15 μA cm⁻² photocurrent response of the PP/C₆₀bar film deposited onto an ITO electrode was produced under the irradiation of 20 mW cm⁻² white light, indicating the presence of photo-induced electron transfer between PP and C₆₀bar. TEM images showed that spherical particles were fabricated by the self-assembly of PP and C₆₀bar through hydrogen-bonding interaction.     

Reaction of [60]fullerene with CF3COOHal affords an unusual 1,3-dioxolano-[60]fullerene

Reaction of C₆₀ with acyl hypohalogenites CF₃COOBr or CF₃COOI in the presence of water affords an orthoester-type 1,3-dioxolanofullerene in 40-50% yield. This method cannot be applied for the synthesis of 1,3-dioxolanofullerenes bearing aryl- or alkyl-groups since they undergo non-selective halogenation under the reaction conditions.     

Synthesis of a linear benzo[3]phenylene-[60]fullerene dyad

The synthesis of a new linear benzo[3]phenylene-[60]fullerene dyad 1 is achieved over 10 steps in 15% overall yield by using an efficient sequence combining a double cobalt(I)-mediated cyclotrimerization with a Bingel reaction.     

Energies of charge transfer and supramolecular interactions of some mono O-substituted calix[6]arenes with [60]fullerene by absorption spectrometric method

Equilibria for the formation of supramolecular complexes of [60]fullerene with a series of mono O-substituted calix[6]arenes, namely: (i) 37-methoxy-38,39,40,41,42-pentahydroxy-5,11,17,23,29,35-hexa(4-tert-butyl)calix[6]arene (1), (ii) 37-allyl-38,39,40,41,42-pentahydroxy-5,11,17,23,29,35-hexa(4-tert-butyl)calix[6]arene (2), (iii) 37-phenacyl-38,39,40,41,42-pentahydroxy-5,11,17,23,29,35-hexa(4-tert-butyl)calix[6]arene (3), (iv) 37-ethylester-38,39,40,41,42-pentahydroxy-5,11,17,23,29,35-hexa(4-tert-butyl)calix[6]arene (4) and (v) 37-benzyl-38,39,40,41,42-pentahydroxy-5,11,17,23,29,35-hexa(4-tert-butyl)calix[6]arene (5) have been studied in CCl4 medium by absorption spectroscopic technique. The stoichiometry has been found to be 1:1 ([60]fullerene:calix[6]arene) in each case. An absorption band due to charge transfer (CT) transition is observed in each case in the visible region. The vertical ionisation potentials (I(D)(v)) of all the calix[6]arenes under study have been estimated utilising CT transition energy. The experimental I(D)(v) values also yield a good estimate of the electron affinity of [60]fullerene. The degrees of CT in the ground state of the complexes have been found to be very low (about 0.15%). Resonance energy of the complexes have been estimated. Thermodynamic parameters for the supramolecular complex formation of [60]fullerene with mono O-substituted calix[6]arene receptors are reported. It is observed that among the calix[6]arenes under the present study, only 1 and 4 form inclusion complexes with [60]fullerene. This has also been substantiated by theoretical calculation using PM3 method. Thus presence of one substituent group (of different types) on the lower rim of the calix[6]arene molecule has been shown to govern the host-guest complexation process.     

Classical molecular dynamics study of [60]fullerene interactions with silica and polyester surfaces

This study examines the interaction of neutral and charged fullerenes with model silica and polyester surfaces. Molecular dynamics simulations at 298 K indicate that van der Waals forces are sufficiently strong in most cases to cause physisorption of the neutral fullerene particle onto the surfaces. The fullerenes are unable to penetrate the rigid silica surface but are generally able to at least partially infiltrate the flexible polymer surface by opening surface cavities. The introduction of charge to the fullerene generally leads to an increase in both the separation distance and Work of Separation with silica. However, the charged fullerenes generally exhibit significantly closer and stronger interactions with polyester films, with a distinct tendency to absorb into the "bulk" of the polymer. The separation distance and Work of Separation of C60 with each of the surfaces also depend greatly on the sign, magnitude, and localization of the charge on the particle. Cross-linking of the polyester can improve resistance to the neutral fullerene. Functionalization of the polyester surface (F and OH substituents) has been shown to prevent the C60 from approaching as close to the polyester surface. Fluorination leads to improved resistance to positively charged fullerenes, compared to the unmodified polyester. However, hydroxylation generally enables greater adhesion of charged fullerenes to the surface due to H-bonding and electrostatic attraction.     

Thermodynamic Insight into the Origin of a Calix[n]arene-[60]fullerene Interaction and its Application to a Porphyrin-[60]fullerene Energy Transfer System

The calixarene-fullerene interaction,which causes only a slight change in the absorptionspectra, has been substantiated by calorimetricmeasurements: the H° values arecomparable with those obtained from the associationconstants estimated by a spectroscopic method. Furthermore, we determined the association constantbetween homooxacalix[3]arene and [60]fullerenederivatives with a porphyrin moiety by fluorescencespectra.     

Dimeric capsules with a nanoscale cavity for [60]fullerene encapsulation

The acid-assisted and guest-induced formation of superstructures was achieved by the addition of haloacetic acids to a toluene solution of the resorcin[4]arene derivatives 1 and [60]fullerenes. The formation of dimeric superstructures that encapsulated a nanosized guest molecule was observed when appropriate acids, such as haloacetic acids, and suitable guest molecules, such as [60]fullerenes, were co-added to a toluene solution of cavitand 1 that has four pyridine units, whereas a complicated equilibrium between several species was detected without [60]fullerenes, and the formation of discrete superstructures was not monitored in the absence of haloacetic acids. The spectroscopic data indicate that the formed [60]fullerene-encapsulated complexes have the structure of 2. These complexes are self-assembled through pyridinium-anion-pyridinium interactions and by pi-pi and van der Waals interactions. The rate of decomplexation of 2 is estimated to be 3.1 s(-1) from a 2D exchange NMR spectrum. The [60]fullerene encapsulation process can be controlled by modifying the amounts of acids used, changing the temperature of the system, altering the ratio of acid/base, and even through varying the solvent polarity. Moreover, the fluorescence spectra show band-narrowing spectral changes and a retardation of the relaxation characteristics of isolated and isotropic [60]fullerenes, which indicates that the environmental change around [60]fullerene is induced upon its encapsulation.     

The first synthesis of a methano[60]fullerene with an electron-donating group at the methano-bridge carbon: synthesis and reaction of aminomethano[60]fullerene

[reaction: see text] Aminomethano[60]fullerene was synthesized for the first time as a trifluoromethanesulfonic acid salt by applying the Curtius rearrangement of azidocarbonylmethano[60]fullerene as the key reaction. Aminomethano[60]fullerene thus obtained was found to be able to react with various acyl chlorides to afford the corresponding amides.     

Supramolecular complexation studies of [60]fullerene with calix[4]naphthalenes—a reinvestigation

Estimations of equilibrium or association constant (K_ASSOC) values reported by many other groups for the supramolecular complexation between [60]fullerene (‘C₆₀’) with different macrocyclic hosts, in solvents such as toluene or carbon disulfide, for example, is often conducted by UV-vis absorption and/or ¹H NMR spectroscopy. In this paper, the complexation behaviour of two calix[4]naphthalene hosts with C₆₀ in toluene and carbon disulfide has been re-examined, using both of these methods. An analysis is presented of the data newly obtained, in light of recent advances and understanding published by others of the limitations of, in particular, the absorption spectroscopic methods. The discussion presented is also intended to aid those who may be unfamiliar with the nuances and limitations of the analytic models involving C₆₀ supramolecular complexation. Also presented is a general mechanism for C₆₀ supramolecular complexation studies, which lay the groundwork for further experiments.     

Synthesis of a proline-rich [60]fullerene peptide with potential biological activity

A proline-rich [60]fullerene peptide was synthesized by use of (i) a 1,3-dipolar cycloaddition of an N-substituted glycine derivative to [60]fullerene, (ii) esterification of the isolated alcohol with the C-terminal amino acid of the desired peptide sequence, and finally (iii) coupling of the remaining hexapeptide to give the final product 8 as a TFA salt, with oxidized methionine. Product 8 was found to be biologically active against sera from MCTD and SLE patients (ELISA experiment).     

Molecular photoelectric switch using a mixed SAM of organic [60]fullerene and [70]fullerene doped with a single iron atom

We describe a photoswitch fabricated on indium tin oxide (ITO) as a self-assembled monolayer (SAM) of two fullerene molecules, a purely organic [60]fullerene that generates an anodic current and a [70]fullerene doped with a single iron atom. This device generates a bidirectional photocurrent upon irradiation at 340 and 490 nm. The new [70]fullerene iron complex bearing three rigid carboxylic acid legs, Fe[C(70)(C(6)H(4)C(6)H(4)COOH)(3)]Cp, generates only a cathodic current upon photoexcitation between 350 and 700 nm, whereas the organic [60]fullerene absorbs at wavelengths shorter than 500 nm. The quantum efficiency of the photocurrent generation by the mixed SAM is comparable to that of a single-component SAM, indicating that the individual diode molecules on ITO generate photocurrents independently with little cross talk.     

Synthesis and properties of polyamides with [60]fullerene in the main chain

A novel series of polyamides having [60]fullerene moieties in the main chain were synthesized by a direct polycondensation of [60]fullerenobis(acetic acid) or [60]fullerenobis(acetic acid)/isophthalic acid mixture with a diamine in the presence of triphenyl phosphite and pyridine. Various properties of the polyamides were characterized by means of IR, GPC, TGA, DSC, UV–visible, and photoluminescence. The molecular weight M_w of the [60]fullerene-containing polyamides was observed in the range from about 300,000 to 3,000; upon the changing of the ratio of [60]fullerenobis(acetic acid)/isophthalic acid in the starting mixture, the resulting M_w decreased with increasing the ratio. Most of the thermal and optical properties gradually changed as the ratio changed; the major optical absorption band in visible range exhibited a significant tailing, which shifted toward a longer wavelength, while the photoluminescence spectrum red-shifted with increasing [60]fullerene content. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 3139–3146, 1998     

Photoinduced processes in a tricomponent molecule consisting of diphenylaminofluorene-dicyanoethylene-methano[60]fullerene

Photoinduced intramolecular processes in a tricomponent molecule C60(>(CN)2-DPAF), consisting of an electron-accepting methano[60]fullerene moiety (C60>) covalently bound to an electron-donating diphenylaminofluorene (DPAF) unit via a bridging dicyanoethylenyl group [(CN)2], were investigated in comparison with (CN)2-DPAF. On the basis of the molecular orbital calculations, the lowest charge-separated state of C60(>(CN)2-DPAF) is suggested to be C60*-(>(CN)2-DPAF*+) with the negative charge localized on the fullerene cage, while the upper state is C60(>(CN)2*--DPAF*+). The excited-state events of C60(>(CN)2-DPAF) were monitored by both time-resolved emission and nanosecond transient absorption techniques. In both nonpolar and polar solvents, the excited charge-transfer state decayed mainly through initial energy-transfer process to the C60 moiety yielding the corresponding 1C60, from which charge separation took place leading to the formation of C60*-(>(CN)2-DPAF*+) in a fast rate and high efficiency. In addition, multistep charge separation from C60(>(CN)2*--DPAF*+) to C60*-(>(CN)2-DPAF*+) may be possible with the excitation of charge-transfer band. The lifetimes of C60*-(>(CN)2-DPAF*+) are longer than the previously reported methano[60]fullerene-diphenylaminofluorene C60(>(C=O)-DPAF) with the C60 and DPAF moieties linked by a methanoketo group. These findings suggest an important role of dicyanoethylenyl group as an electron mediating bridge in C60(>(CN)2-DPAF).     

Synthesis of a single isomer of the bis-adduct of isocyanurato-substituted azide with [60]fullerene

A single di(azahomo)[60]fullerene isomer was prepared for the first time by the reaction between [60]fullerene and isocyanurato-substituted azide. The structure of the product was established by ¹H and ¹³C NMR, UV, and IR spectroscopy.     

The first trisaza-bridged [60]fulleroid: drilling a hole on the fullerene

[reaction: see text] Two types of trisaza-bridged [60]fulleroids have been synthesized for the first time. By means of (13)C NMR, (1)H NMR, MALDI-TOF MS, FTIR, UV-vis, and 2D-NMR (gHSQC, gHMBC, and NOSEY) spectroscopy, they have been shown to be tris[6,5]-opened-aza-bridged adducts with substituents on the same five-membered ring with C(s)() symmetry. Some data of nonlinear optics and electrochemistry for the product are also reported.