Computer modeling of C2 cluster addition to fullerene C60

The reaction between C₂ cluster and C₆₀ fullerene resulting in C₂ insertion to C₆₀ with formation of closed C₆₂ cage (reaction of C₂ ingestion by C₆₀) was investigated by the semiempirical MNDO‐PM3 method. The geometries and energies of extremal points on the C₆₂ potential energy surface were calculated. Several reaction pathways leading to the formation of three different closed C₆₂ fullerenes were investigated. All insertion reactions proceed stepwise through intermediate adducts of different structures. The main reaction pathways were found to be addition of C₂ by its one side to the 6,6‐ or 5,6‐bond of C₆₀ with formation of primary unclosed C₆₂ adducts of “ball‐with‐fork” structures, lying in deep potential wells. Back reaction of C₂ detachment from primary adducts can compete with that of their transformation to the closed C₆₂ cages inasmuch as calculated activation barriers of the both reactions are comparable. Model calculations at the B3LYP/6‐31G* level, using C₃₂H₁₂ semisphere instead of C₆₀, confirmed the conclusion about two competitive pathways of the primary adducts transformation, C₂ detachment, and C₂ ingestion. The concerted insertion of C₂ to C₆₀ was realized only in the case of severe restrictions on starting geometry of the C₂ + C₆₀ system. The results of calculations explain recent experimental data on the formation of metastable adducts upon addition of C₂ to C₆₀, obtained using the time‐of‐flight mass spectrometer with laser desorption. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

Synthesis and Photoconductivity Study of C60‐Containing Styrene/Acrylamide Copolymers

The C₆₀‐containing copolymers were prepared by reaction of styrene (St)/acrylamide (Am) copolymers with C₆₀ in toluene. By means of UV‐Vis spectroscopy, the C₆₀ content in the copolymers was determined to be up to 1.45 wt.‐%. The results show that with increasing the amide molar fraction in the copolymers, the C₆₀ content increases and the molar ratio C₆₀/amide group decreases. It was also revealed that the reactivity of the amide group with respect to C₆₀ could be enhanced by increasing the reaction temperature. C₆₀‐containing St/Am copolymers were characterized by DSC, GPC, XRD and UV‐Vis spectroscopy. Experimental results indicate that these C₆₀‐containing polymers reveal good photoconductivity, with the t_1/2 value of the better one (B8) being about 1.88 s, and photoconductivity could be enhanced on increasing the C₆₀ content in the copolymers.     

Synthesis and Characterization of a Novel Class of PPV Derivatives Covalently Linked to C60

Poly(phenylenevinylene) (PPV) derivatives covalently linked to fullerene C₆₀ (PPV‐1‐C₆₀ and PPV‐2‐C₆₀) were synthesized by cycloaddition reaction between C₆₀ and azide group‐containing PPV derivatives. By tuning the initial feed ratio of the azido monomer, the content of C₆₀ in the copolymers was controlled. The copolymers were partially soluble in common organic solvents and were characterized by means of ¹H NMR, FT‐IR, UV‐Vis and fluorescence spectroscopy, as well as by GPC, TGA and cyclic voltammetry techniques.     

New approaches for the synthesis of hindered C60‐containing polyphosphazenes via functionalized intermediates

Two new approaches were developed to synthesize C₆₀‐containing polyphosphazenes. Accordingly, two new reactive macromolecular intermediates ( P4 and P8 ) were obtained from poly(dichlorophosphazene) by the direct nucleophilic substitution reaction. In one approach, a predesigned amimo end–functionalized polyphosphazene ( P4 ) was prepared and then reacted with C₆₀ molecules in chlorobenzene to yield C₆₀‐containing polyphosphazene; in the other approach, a polyphosphazene containing 4‐methyl phenoxy groups as side chains was first prepared, and then part of the 4‐methyl groups were converted to azidomethyl groups (in P8 ), which reacted with C₆₀ to yield C₆₀‐containing polyphosphazene. The polymers were characterized by ¹H NMR, ¹³C NMR, IR, and UV–visible spectra and by gel permeation chromatography. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2877–2885, 2004     

A Convenient Synthesis of Novel Meldrum＇s Acid C60 Fullerene Derivatives

A series of novel Meldrum＇s acid C60 derivatives were prepared in moderate yields from a convenient one-pot reaction of C60, the Meldrum＇s acid derivatives, 12 and 1,8-diazabicyclo-[5,4,0]-undec-7-ene （DBU） in toluene at room temperature under nitrogen atmosphere. All the new compounds were fully characterized by the spectral data and elemental analysis. A carbene intermediate mechanism was proposed for this reaction.     

Synthesis of C60‐containing polyphosphazenes from a new reactive macromolecular intermediate: Polyphophazene azides

A novel synthetic strategy was developed to prepare polyphosphazenes containing C₆₀ moieties as side chains. Thus, a new reactive macromolecular intermediate, polyphosphazene azides ( P1 ), was obtained from poly(dichlorophosphazene) by the direct nucleophilic substitution reaction. Then the azide group in P1 reacted with C₆₀ molecules to afford the first example of C₆₀‐containing polyphosphazenes ( P2 and P3 ). The polymers are soluble in common organic solvents. Molecular structural characterization for the polymers was presented by ¹H NMR, ¹³C NMR, IR, ultraviolet–visible spectra, and gel permeation chromatography. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 194–199, 2004     

First Homopolymerizable Monomer Containing [C60]Fullerene as a Monoadduct Substituent

Summary: The hydrosilylation of C₆₀ with 2,4,6,8‐tetramethylcyclotetrasiloxane in the presence of platinum/carbon catalyst produced the cationically polymerizable (C₆₀HsiMeO)₄ along with [(C₆₀HsiMeO)₃SiMeO]₂C₆₀H₂ and a polymer consisting of C₆₀ and (SiMeO)₄ units. The synthesis and characterization of this first polymerizable tetracyclosiloxane ring system containing C₆₀ as a monoadduct substituent are also reported.

Synthesis and polymerization of 2,4,6,8‐tetramethyl‐2,4,6,8‐tetrafulleryl‐cyclotetrasiloxane.     

Alternative Synthesis of C60‐Diphenylaminofluorene Derivatives for Nonlinear Photonic Applications: Method of Preparation and Characterization

An alternative synthetic route for the preparation of key intermediate synthons 7‐α‐bromoacetyl‐2‐diphenylaminofluorene (α‐BrDPAF‐H) and 7‐α‐bromoacetyl‐9,9‐dialkyl‐2‐diphenylaminofluorene (α‐BrDPAF‐C_n) was demonstrated. The latter reactions involved the first step of dialkylation of 2‐bromofluorene at C₉ position of the fluorene moiety, the second step of a diphenylamino group attachment at C₂ position of the resulting dialkylfluorene, and the third step of Friedel‐Craft acylation of α‐bromoacetyl group at C₇ position of dialkylated diphenylaminofluorene. From the intermediates α‐BrDPAF‐H and α‐BrDPAF‐C_n, a series of C₆₀‐keto‐DPAF nanostructures, such as the fullerene monoadducts C₆₀(>DPAF‐H) and C₆₀(>DPAF‐C_n), where n is 2, 4, or 10, were synthesized in a reasonable yield. Molecular mass ions of the dyads C₆₀(>DPAF‐H), C₆₀(>DPAF‐C₂), C₆₀(>DPAF‐C₄), and C₆₀(>DPAF‐C₁₀) were clearly detected in positive ion matrix‐assisted laser desorption ionization mass spectrum (MALDI–MS) that confirmed the composition mass of each compound synthesized.     

NMR Properties of Polylithiated C60

Endohedral, ¹³C, ⁷Li, and nucleus‐independent (NICS) chemical shifts are reported for selected Li_nC₆₀ isomers (n = 6, 12, 18) at the GIAO (gauge‐including atomic orbitals)‐SCF/DZP//BP86/3–21G level. Li₆C₆₀ closely resembles C₆₀^6– in terms of NMR criteria for aromaticity, as evidenced by an exceptionally high endohedral shielding. In contrast, nonaromaticity is indicated for Li₁₂C₆₀, based on a positive endohedral chemical shift. NICS and δ(endo) values very similar to those of Li₁₂C₆₀ are obtained for Li₁₈C₆₀. According to population analysis, indeed the same number of electrons are transferred to the fullerene cage in both cases. Endohedral chemical shifts, accessible via ³He NMR of the corresponding endohedral helium compounds, could thus be a valuable indicator for the extent of reduction of the C₆₀ molecule. Energetic estimates suggest that in the bulk, Li₁₂C₆₀ should be unstable with respect to decomposition into Li₆C₆₀ and lithium metal.     

Photophysical Properties and Photoinduced Electron Transfer between[60]Fullerene—containing Cyclic Sulphoxide [C60—C60H8SO]and Tetrathiafulvalene（TTF） by Laser Flash Photolysis

Photoinduced electron transfer(PET) processes between C60-C6H8SO and Tetrathiafulvalene(TTF) have been studied by nanosecond laser photolysis.Quantrm yiekds(φet) and rate constants of electron transfer(ket) from TTF to excited triplet state of[60] fullerene-containing cyclic sulphoxide in benzonitrile(BN) have been evaluated by observing the transient absorption bands in the NIR region.With the decay of excited triplet state of [60]fullerene-containing cyclic suplhoxide,the rise of radical anion of [60]fullerene-containing cyclic sulphoxinde is observed.     

Preparation and properties of polyethoxysilsesquioxane‐C60 hybrids

Free‐standing films of C₆₀‐polyethoxysiloxane hybrids were prepared, and their optical limiting properties were evaluated. Triethoxysilylated C₆₀, with a formula of H₃C₆₀[Si(OEt)₃]₃, was synthesized by the hydrolysilylation of C₆₀ with triethoxysilane in the presence of platinum catalyst. C₆₀‐polyethoxysiloxanes were prepared by a cohydrolytic polycondensation of triethoxysilylated C₆₀ with tetraethoxysilane in a molar ratio of Si/C₆₀ = 10–1000 under nitrogen flow. The molecular weight of C₆₀‐polyethoxysiloxane increased with a decrease of Si/C₆₀. Transparent and flexible free‐standing films were prepared by aging an ethanol solution of C₆₀‐polyethoxysiloxane at 80 °C for 6–8 days. The mechanical strength and Young's modulus increased with a decrease in Si/C₆₀. These free‐standing films showed an optical limiting property, for which the threshold value decreased from 1163 mJ/cm² (Si/C₆₀ = 1000) to 130 mJ/cm² (Si/C₆₀ = 10) with a decrease of Si/C₆₀. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3273–3279, 2007     

Phthalocyanine–C60 Fused Conjugates Exhibiting Molecular Orbital Interactions Depending on the Solvent Polarity

New covalently C₆₀‐connected zinc phthalocyanine (ZnPc) derivatives have been synthesized by utilizing successive cycloaddition reactions of C₆₀ with a ZnPc derivative containing a pyridazine moiety employing Komatsu’s method in reaction of C₆₀ with phthalazine. The UV/Vis absorption spectrum of the fused conjugate ( 5 ) shows red shifts from the corresponding absorption of ZnPc derivative ( 8 ), indicating interactions between the ZnPc and C₆₀ moieties. The DFT calculations under non‐polar medium predict that the HOMO and LUMO of 5 localize on the ZnPc moiety, whereas LUMO+1 localizes on the C₆₀ moiety, which reasonably explain the magnetic circular dichroism (MCD) and absorption spectra in toluene. Electrochemical redox potentials of 5 in polar solvents indicate the first‐oxidation potential arises from the ZnPc moiety, whereas the first reduction potential is associated with the C₆₀ moiety, suggesting the LUMO localizes on the C₆₀ moiety in polar solvent. This reversal of the LUMO is supported by the ZnPc‐fluorescence quenching with a nearby C₆₀ moiety in benzonitrile, which leads to the charge‐separation via the excited singlet state of the ZnPc moiety. In toluene on the other hand, such a ZnPc‐fluorescence quenching owing to the photoinduced charge separation is not observed as predicted by the DFT‐calculated LUMO on the ZnPc moiety.     

Preparation and Properties of C60-Polysiloxane Hybrids

C₆₀-polysiloxane hybrids were prepared by the reaction of triethoxysilylated C₆₀ (TES-C₆₀) with methylpolysiloxane (MPS) or , -dihydroxypolydimethylsiloxane (STPDS). TES-C₆₀ was synthesized by hydrosilylation using triethoxysilane and C₆₀ in the presence of chloroplatinic acid. TES-C₆₀ was mixed with MPS and heated to provide a bulk body of C₆₀ containing polysiloxane hybrid in a Si/C₆₀ molar ratio of 1000:500. The formation of this hybrid is based on the hydrolytic polycondensation of TES-C₆₀ and MPS to fix C₆₀ into the silica matrix by a chemical bond. TES-C₆₀ and STPDS also provide an isolatable thin film of C₆₀ containing polysiloxane hybrid by an ethanol-forming condensation reaction. Because no gelation was observed when only STPDS was aged, it is thought that TES-C₆₀ serves as a cross-linking point in gel formation.     

Dimerization of C60: Symmetry Considerations

Orbital‐symmetry analysis (OCAMS) of the dimerization of C₆₀ via [2+2] cycloaddition indicates that the reactant monomers should approach one another along a pathway in which C_2h symmetry is conserved. Point‐by‐point computations (AM1/UHF) confirm this prediction: a low‐energy pathway leads to a single‐bonded dimer 2 with C_2h symmetry. Closure to the stable D_2h dimer 1 is effected by relatively facile rotation about the single bond. A similar symmetry analysis was performed on a second isomer 3 with D_2h symmetry, the moieties of which are linked by two two‐atom chains. It raises the possibility that 3 , the so‐called `window' isomer, may be interconvertible with 1 along a pathway that retains C_i (S₂) symmetry. Although the computational results indicate that C₆₀ is in thermal equilibrium with its stable dimer 1 at moderate temperatures, the latter is not observed in the gas phase for thermodynamic reasons. According to THERMO computations (AM1/RHF), the equilibrium is shifted strongly towards the monomer pair at temperatures where vaporization of the solid C₆₀ is observed (>400°).     

Solubilization of C60 by micellization with a thermoresponsive block copolymer in water: Characterization,singlet oxygen generation,and DNA photocleavage

Water‐soluble diblock copolymer, poly(N‐isopropylacrylamide)‐block‐poly(N‐vinyl‐2‐pyrroridone) (PNIPAM_m‐b‐PNVP_n), was found to associate with fullerene (C₆₀), and thus C₆₀ can be solubilized in water. The 63C₆₀/PNIPAM_m‐b‐PNVP_n micelle formed a core‐shell micelle‐like aggregate comprising a C₆₀/PNVP hydrophobic core and a thermoresponsive PNIPAM shell. The C₆₀‐containing polymer micelle formation and its thermoresponsive behavior were characterized using light scattering and ¹H NMR techniques. The hydrodynamic radius (R_h) of the C₆₀‐bound polymer micelle increased with increasing temperature, which was ascribed to the hydrophobic association between dehydrated PNIPAM shells above lower critical solution temperature (LCST). ¹H NMR data suggest that the motion of the PNIPAM block is restricted above LCST due to the dehydration of the PNIPAM shell in water. The generation of singlet oxygen by photosensitization by the C₆₀‐bound polymer micelle was confirmed from photooxidation of 9,10‐anthracenedipropionic acid. Furthermore, DNA was found to be cleaved by visible light irradiation in the presence of the C₆₀‐bound polymer micelle. Therefore, there may be a hope for a pharmaceutical application of the C₆₀‐bound polymer micelle to cancer photodynamic therapy. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Synthesis of Poly(vinyl alcohol)/C60 and Poly(N‐vinylpyrrolidone)/C60 Nanohybrids as Potential Photodynamic Cancer Therapy Agents

Well‐defined poly(vinyl acetate) (PVAc) and poly(N‐vinylpyrrolidone)‐co‐poly(vinyl acetate) (PNVP‐co‐PVAc) chains end‐capped by Co(acac)₂ (acac=acetylacetonate) and prepared by cobalt‐mediated radical polymerization (CMRP) are grafted onto a fullerene. Homolytic Co? C bond cleavage of the polymer chain ends at 30 °C releases the polymeric radicals that add onto C₆₀, thereby leading to the corresponding PVAc/C₆₀ and PNVP‐co‐PVAc/C₆₀ nanohybrids. The [polymer–Co(acac)₂]/[C₆₀] molar ratio was varied to adjust the structure of the nanohybrids, and more particularly the number of grafted arms. Finally, the potential of the hydrosoluble PVOH/C₆₀ nanohybrids, which result from the methanolysis of the ester groups of PVAc/C₆₀, and of the PNVP‐co‐PVAc/C₆₀ nanohybrids as photosensitizers for photodynamic therapy (PDT), was approached. First, photobleaching tests demonstrated the ability of these nanohybrids to produce singlet oxygen upon irradiation, which can play a role in cell damage. Second, cell viability assays demonstrated that both types of nanohybrids are deprived of intrinsic cytotoxicity in the dark, whereas they promoted significant cell mortality when subjected to light treatment. The selective response of these materials to irradiation makes them promising compounds for PDT.     

Tether‐Directed Bisfunctionalization Reactions of C60 and C70

Four easily isolable regio‐ and stereoselective bis‐adducts of C₆₀ and C₇₀, as well as a new C₇₀‐dumbbell derivative, have been synthesized by using two different bismalonate tethered moieties. The derivatives that possess relatively long‐tethered moieties show highly symmetric addition patterns, as evidenced by spectroscopic measurements, whereas the derivatives possessing the shorter‐tethered moiety exhibit interesting addition patterns on C₆₀ and C₇₀.     

An Isomer of C60Cl10 Free of Skew‐Pentagonal‐Pyramidal C60Cl6 Substructure

Chlorination is an effective approach for understanding the feature of multiple additions on fullerene cages. The chlorofullerenes obtained are versatile synthons for further derivatization. However, chlorofullerenes used for chemical reaction studies are mainly based on the skew‐pentagonal‐pyramidal (SPP) C₆₀Cl₆. In this work, a new isomer of C₆₀Cl₁₀ that does not contain an SPP‐C₆₀Cl₆ substructure was identified. Its electrochemical properties give it unexpected cyclic voltammetric behavior at more negative potentials relative to other chlorofullerenes. Friedel–Crafts arylation shows good reactivity of this compound. These new findings challenge opinions of fullerene addition patterns and will break the monopoly of C₆₀Cl₆ as a precursor for fullerene modifications.     

Molecular view of charge exchange in ion–C60 collisions

We present a theoretical study of charge transfer in H⁺+C₆₀ and He²⁺+C₆₀ collisions using an extension of the molecular time‐dependent method of ion–atom collisions. Energy‐correlation diagrams have been evaluated for the corresponding (C₆₀–H)⁺ and (C₆₀–He)²⁺ quasi‐molecules. Single and double charge‐transfer cross sections in C₆₀+He²⁺ collisions are reported for the first time. The results show that double charge‐transfer cross sections are only one order of magnitude smaller than single charge‐transfer cross sections. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001     

Starburst Encapsulation of C60 by Multiple Hindered Two‐Photon Absorptive Diphenylaminodialkylfluorene Arms

The efficiency of nonlinear optical responses is highly influenced by the state of molecular assembly and aggregation. Introduction of bulky alkyl groups on an organic chromophore enhances its molecular dispersion in solution and, thus, simultaneous multiphoton absorptivity. Accordingly, sterically hindered fullerenyl chromophore triads C₆₀(>DPAF‐C₉)₂ and pentads C₆₀(>DPAF‐C₉)₄ were designed and synthesized for the use as optical limiting materials. Photoinduced molecular polarization is a crucial parameter for the enhancement of nonlinear optical responses. For this purpose, we synthesized these conjugates by attaching one or several diphenylaminofluorene moieties to methano[60]fullerene via a covalent keto linkage. The motif increases electronic interactions of DPAF‐C_n rings with the C₆₀ cage in close vicinity. Synthesis of C₆₀(>DPAF‐C₉)_n (n=1, 2, or 4) was carried out by a four‐step reaction procedure starting from 2‐bromofluorene via dialkylation at C₉ position of fluorine ring and followed by attachment of a diphenylamino group at C₂ position of dialkylated fluorene, acylation of α‐bromoacetyl group at C₇ position of diphenylaminodialkylfluorene, and subsequent Bingel cyclopropanation of DPAF‐acyl bromide with C₆₀. All C₆₀‐DPAF‐C_n derivatives were fully characterized by various spectroscopic analyses. Molecular compositions of these conjugates were clearly confirmed by MALDI‐TOF mass spectra. A method of relative proton counting was applied on the samples of complex C₆₀(>DPAF‐C₉)₂ and C₆₀(>DPAF‐C₉)₄ derivatives using DABCO as an internal standard for the calibration of proton integration in ¹H‐NMR spectroscopic analyses.