First Unsymmetrical Bisfullerene, C121: Evidence for the Presence of Both Homofullerene and Methanofullerene Cages in One Molecule

Tightly Bound Double-Caged [60]Fullerene Derivatives with Enhanced Solubility: Structural Features and Application in Solar Cells

A series of novel highly soluble double-caged [60]fullerene derivatives were prepared by means of lithium-salt-assisted [2+3] cycloaddition. The bispheric molecules feature rigid linking of the fullerene spheres through a four-membered cycle and a pyrrolizidine bridge with an ester function CO₂ R (R=n-decyl, n-octadecyl, benzyl, and n-butyl; compounds 1 a-d, respectively), as demonstrated by NMR spectroscopy and X-ray diffraction. Cyclic voltammetry studies revealed three closely overlapping pairs of reversible peaks owing to consecutive one-electron reductions of fullerene cages, as well as an irreversible oxidation peak attributed to abstraction of an electron from the nitrogen lone-electron pair. Owing to charge delocalization over both carbon cages, compounds 1 a-d are characterized by upshifted energies of frontier molecular orbitals, a narrowed bandgap, and reduced electron-transfer reorganization energy relative to pristine C₆₀ . Neat thin films of the n-decyl compound 1 a demonstrated electron mobility of (1.3±0.4)×10^-3  cm²  V^-1  s^-1 , which was comparable to phenyl-C₆₁ -butyric acid methyl ester (PCBM) and thus potentially advantageous for organic solar cells (OSC). Application of 1 in OSC allowed a twofold increase in the power conversion efficiencies of as-cast poly(3-hexylthiophene-2,5-diyl) (P3HT)/1 devices relative to the as-cast P3HT/PCBM ones. This is attributed to the good solubility of 1 and their enhanced charge-transport properties - both intramolecular, owing to tightly linked fullerene cages, and intermolecular, owing to the large number of close contacts between the neighboring double-caged molecules. Test P3HT/1 OSCs demonstrated power-conversion efficiencies up to 2.6 % (1 a). Surprisingly low optimal content of double-caged fullerene acceptor 1 in the photoactive layer (≈30 wt %) favored better light harvesting and carrier transport owing to the greater content of P3HT and its higher degree of crystallinity.

Building Carbon Bridges on and between Fullerenes in Helium Nanodroplets

We report the observation of sequential encounters of fullerenes with C atoms in an extremely cold environment. Experiments were performed with helium droplets at 0.37 K doped with C60 molecules and C atoms derived from a novel, pure source of C atoms. Very high-resolution mass spectra revealed the formation of carbenes of the type C60(C:)n with n up to 6. Bridge-type bonding of the C adatoms to form the known dumbbell C60═C═C60 also was observed. Density functional theory calculations were performed that elucidated the carbene character of the C60(C:)n species and their structures. Mass spectra taken in the presence of water impurities and in separate experiments with added H2 also revealed the formation of the adducts C60C(n)(H2O)n and C60C(n)(H2)n probably by H-OH and H-H bond insertion, respectively, and nonreactivity for the dumbell. So C adatoms that form carbenes C60(C:)n can endow pristine C60 with a higher chemical reactivity.

Photochemical and Photophysical Properties of Three Carbon-Bridged Fullerene Dimers: C121 (I, II, III)

The photochemical and photophysical properties of the three C121 isomers (I, II, III) were investigated with MADLI-TOF-MS, UV-vis spectra, fluorescence spectra, absorption spectra of their DMA complexes, and theoretical calculations. The three isomers of C121 (I, II, III) have different stabilities under laser irradiation, but isomer I and isomer II show good stability against the heat-induced conversion between different isomers: No conversion between the isomers was found after heating the mixture of isomer I and isomer II at 353 K for 12 h in Ar atmosphere. The results of UV-vis absorption and fluorescence spectra indicate that interactions between two C60 moieties of C60=C=C60 in the ground and singlet states are not significant, C121 (I, II, III) behaves as an electron-acceptor similar to C60. These indicate that the formation of the fullerene chain structure (e.g., C60=C=C60) does not disturb the photochemical and photophysical properties of the C60 monomer itself, even that the properties were enhanced by the formation of the polymer. This is significant for the C60 polymer in photochemical or photoelectronic applications in which C60=C=C60 can be an excellent basic unit of polymers.

Synthetic, Electrochemical, and Theoretical Studies of Tetrairidium Clusters Bearing Mono- and Bis[60]fullerene Ligands

Heating a mixture of Ir(4)(CO)(9)(PPh(3))(3) (1) and 2 equiv of C(60) in refluxing chlorobenzene (CB) affords a "butterfly" tetrairidium-C(60) complex Ir(4)(CO)(6){mu(3)-kappa(3)-PPh(2)(o-C(6)H(4))P(o-C(6)H(4))PPh(eta(1)-o-C(6)H(4))}(mu(3)-eta(2):eta(2):eta(2)-C(60)) (3, 36%). Brief thermolysis of 1 in refluxing chlorobenzene (CB) gives a "butterfly" complex Ir(4)(CO)(8){mu-k(2)-PPh(2)(o-C(6)H(4))PPh}{mu(3)-PPh(2)(eta(1):eta(2)-o-C(6)H(4))} (2, 64%) that is both ortho-phosphorylated and ortho-metalated. Interestingly, reaction of 2 with 2 equiv of C(60) in refluxing CB produces 3 (41%) by C(60)-assisted ortho-phosphorylation, indicating that 2 is the reaction intermediate for the final product 3. On the other hand, reaction of Ir(4)(CO)(8)(PMe(3))(4) (4) with excess (4 equiv) C(60) in refluxing 1,2-dichlorobenzene, followed by treatment with CNCH(2)Ph at 70 degrees C, affords a square-planar complex with two C(60) ligands and a face-capping methylidyne ligand, Ir(4)(CO)(3)(mu(4)-CH)(PMe(3))(2)(mu-PMe(2))(CNCH(2)Ph)(mu-eta(2):eta(2)-C(60))(mu(4)-eta(1):eta(1):eta(2):eta(2)-C(60)) (5, 13%) as the major product. Compounds 2, 3, and 5 have been characterized by spectroscopic and microanalytical methods, as well as by single-crystal X-ray diffraction studies. Cyclic voltammetry has been used to examine the electrochemical properties of 2, 3, 5, and a related known "butterfly" complex Ir(4)(CO)(6)(mu-CO){mu(3)-k(2)-PPh(2)(o-C(6)H(4))P(eta(1)-o-C(6)H(4))}(mu(3)-eta(2):eta(2):eta(2)-C(60)) (6). These cyclic voltammetry data suggest that a C(60)-mediated electron transfer to the iridium cluster center takes place for the species 3(3)(-) and 6(2)(-) in compounds 3 and 6. The cyclic voltammogram of 5 exhibits six well-separated reversible, one-electron redox waves due to the strong electronic communication between two C(60) cages through a tetrairidium metal cluster spacer. The electrochemical properties of 3, 5, and 6 have been rationalized by molecular orbital calculations using density functional theory and by charge distribution studies employing the Mulliken and Hirshfeld population analyses.

Theoretical Study of Unsymmetrical Bisfullerene and Its Derivatives: C131, C129BN, and C130Si

Unsymmetrical bisfullerene C(131) and its derivatives such as C(129)BN and C(130)Si are systematically investigated by semiempirical and density functional theory approaches. In comparison with the experimental data, calculated IR and NMR results reveal that both C(131)(H) and C(131)(P) isomers are possible compounds to coexist in the synthesized product. The C/Si and CC/BN substitution can change the electronic properties and reactivities compared with the pristine C(131)(H) and C(131)(P), respectively.

Preparation of [5,6]- and [6,6]-Oxahomofullerene Derivatives and Their Interconversion by Lewis Acid Assisted Reactions of Fullerene Mixed Peroxides

[60]Fullerene mixed peroxides C60(O)(OOtBu)4 exhibit chemo- and regioselective reactions under mild conditions. The epoxy moiety is opened by ferric chloride to form vicinal hydroxy chloride C60Cl(OH)(OOtBu)4. BF3 is also effective in opening the epoxy moiety. The O-O bond of the fullerene mixed peroxide is cleaved by aluminum chloride to form both [5,6]- and [6,6]-fullerene hemiketals (oxohomo[60]fullerenes). A Hock-type rearrangement is proposed for the formation of the hemiketals, in which a fullerene C-C bond is cleaved. Lewis acids and/or visible light can initiate isomerization of the hemiketal isomers. Single-crystal X-ray analysis and theoretical calculations confirmed the results.

Theoretical studies of structures and stabilities of a new odd-numbered fullerene dimer: C141

The possible isomers of a newly synthesized C(141) molecule are calculated using MNDO, AM1, PM3, B3LYP/3-21G, and B3LYP/6-31G(d) methods. The geometry optimizations showed that the isomer 8-8 has the lowest total energy in all 64 possible structures of C(141). Unlike those of C(130), C(140), etc., the C(141) 8-8 shows a new structure: two C(70) side cages open [6.6] ring junctions located at the equator (instead of cap) area to create new chemical bonds for the bridge atom. Theoretical measurements of the average length of the long and short axes of C(70) side cages in the C(141) molecule reveal that when two C(70) cages are connected with each other at the equators, their geometric shapes become more spherical compared with the pristine C(70); this leads to a reduction of the molecular polarizability. Analysis of the local and global strain indicates that the global strain of C(70) monomer in the C(141) 8-8 is greatly reduced compared to the pristine C(70). The stable C(70) derivatives that are formed with reacted C-C bonds in the equator area may put new insights into fullerene chemistry, in particular, for C(70) to react with a large molecule. The results are discussed together with the experimental data.

Highly Selective and Simple Synthesis of C2m−X−C2n Fullerene Dimers

Energetic-radiation-induced dimerization reaction of fullerenes was found to be a simple and highly selective method for synthesis of C2m-X-C2n (m = n or m not equal n) type molecules without formation of other products. Utilizing the new method, C70-C-C70, C60-C-C70, C60-C-C60, and C70-O-C70 were prepared and characterized. The method is capable of synthesizing new C2m-X-C2n molecules by introducing X (different atoms) into the reaction system. Energetic radiation created reactive sites for covalently bonded bridges between fullerene molecules originally only weakly bound by van der Waals force. This observation may open a new subject and practicable approach for polymer sciences of fullerenes.

Strong Interfullerene Electronic Communication in a Bisfullerene−Hexarhodium Sandwich Complex

Reaction of Rh(6)(CO)(12)(dppm)(2) (dppm = 1,2-bis(diphenylphosphino)methane) with 1.4 equiv. of C(60) in chlorobenzene at 120 degrees C affords a face-capping C(60) derivative Rh(6)(CO)(9)(dppm)(2)(micro(3)-eta(2),eta(2),eta(2)-C(60)) (1) in 73% yield. Treatment of 1 with excess CNR (10 equiv., R = CH(2)C(6)H(5)) at 80 degrees C provides a bisbenzylisocyanide-substituted compound Rh(6)(CO)(7)(dppm)(2)(CNR)(2)(micro(3)-eta(2),eta(2),eta(2)-C(60)) (2) in 59% yield. Reaction of 1 with excess C(60) (4 equiv.) in refluxing chlorobenzene followed by treatment with 1 equiv. of CNR at room temperature gives a bisfullerene sandwich complex Rh(6)(CO)(5)(dppm)(2)(CNR)(micro(3)-eta(2),eta(2),eta(2)-C(60))(2) (3) in 31% yield. Compounds 1, 2, and 3 have been characterized by spectroscopic and microanalytical methods as well as by X-ray crystallographic studies. Electrochemical properties of 1, 2, and 3 have been examined by cyclic voltammetry. The cyclic voltammograms (CVs) of 1 and 2 show two reversible one-electron redox waves, a reversible one-step two-electron redox wave, and a reversible one-electron redox wave, respectively, within the solvent cutoff window. This observation suggests that compounds 1 and 2 undergo similar C(60)-localized electrochemical pathways up to 1(5)(-) and 2(5)(-). Each redox wave of 2 appears at more negative potentials compared to that of 1 because of the donor effect of the benzylisocyanide ligand. The CV of compound 3 reveals six reversible well-separated redox waves due to strong interfullerene electronic communication via the Rh(6) metal cluster bridge. The electrochemical properties of 1, 2, and 3 have been rationalized by molecular orbital calculations using the density functional theory (DFT) method. In particular, the molecular orbital (MO) calculation reveals significant contribution of the metal cluster center to the unoccupied molecular orbitals in 3, which is consistent with the experimental result of strong interfullerene electronic communication via the Rh(6) metal cluster spacer.

Facile Synthesis of Multifullerene-OPE Hybrids via in Situ Ethynylation

[reaction: see text] A series of fullerene-terminated oligo(phenylene ethynylene)s (OPEs) (1a-d and 2) have been synthesized and further characterized by cyclic voltammetry (CV) and UV-vis spectroscopy. The key step in the syntheses is an effective one-pot reaction that allows the attachment of C(60) to multiple terminal alkynes.

Two Metal Centers Bridging Two C60 Cages as a Wide Passage for Efficient Interfullerene Electronic Interaction

The reaction of Ir4(CO)8(PMe3)4 with excess C60 in refluxing 1,2-dichlorobenzene, followed by treatment by CNR (R = CH2C6H5) at 70 degrees C, affords a fullerene-metal sandwich complex Ir4(CO)3(mu4-CH)(PMe3)2(mu-PMe2)(CNR)(mu-eta2,eta2-C60)(mu4-eta1,eta1,eta2,eta2-C60) (1), which exhibits an interesting structural feature of two metal atoms bridging the two C60 centers as well as the first example of a mu4-eta1,eta1,eta2,eta2-C60 bonding mode. Compound 1 has been characterized by NMR spectroscopy, elemental analysis, and X-ray diffraction study. A cyclic voltammetry study reveals strong electronic communication between the two C60 centers in 1, which is due to the presence of a wide channel of two metal centers between the two C60 cages for efficient electronic interaction.

[60]fullerene--metal cluster complexes: novel bonding modes and electronic communication

[60]Fullerene can bind a variety of metal clusters via eta(2)-C(60), mu-eta(2):eta(2)-C(60), and mu(3)-eta(2):eta(2):eta(2)-C(60) pi-type bonding modes. Multiple C(60) additions to a single cluster core have also been demonstrated. Modification of the coordination sphere of cluster moieties has resulted in novel transformation of the coordination mode of the C(60) ligand between pi and sigma (mu(3)-eta(1):eta(1):eta(2)-C(60) and mu(3)-eta(1):eta(2):eta(1)-C(60)) types as well as reversible interconversion between mu(3)-eta(2):eta(2):eta(2)-C(60) and mu-eta(2):eta(2)-C(60). The mu(3)-eta(2):eta(2):eta(2)-C(60) metal cluster complexes show remarkable electrochemical stability and an unusually strong electronic communication between C(60) and metal cluster centers.

The first fullerene-metal sandwich complex: an unusually strong electronic communication between two C(60) cages

Reaction of Rh(6)(CO)(9)(dppm)(2)(mu(3)-eta(2),eta(2),eta(2)-C(60)) (1) with C(60) in refluxing chlorobenzene followed by treatment with CNR (R = CH(2)C(6)H(5)) at room temperature affords the first fullerene-metal sandwich complex Rh(6)(CO)(5)(dppm)(2)(CNR)(mu(3)-eta(2),eta(2),eta(2)-C(60))(2) (2). Compound 2 has been characterized by an X-ray diffraction study. Electrochemical study of 2 reveals six well-separated reversible redox couples localized at C(60) cages due to a strong electronic communication between the two C(60) centers via the Rh(6) cluster spacer.