Visible‐Light‐Mediated Addition of α‐Aminoalkyl Radicals to [60]Fullerene by Using Photoredox Catalysts

The functionalization of fullerene has been extensively studied and various fullerene derivatives have been synthesized. We have succeeded in the functionalization of [60]fullerene by using α‐aminoalkyl radicals generated by visible‐light‐mediated single‐electron oxidation of α‐silylamines as synthetic intermediates. In these reactions, the introduction of diarylamino groups, which are useful electron donors, has been easily achieved.     

Dispersion Interaction Stabilizes Sterically Hindered Double Fullerenes

By state‐of‐the‐art quantum chemical methods, we show that for bulky functional groups like cyclohexane, [20]fullerene, dodecahedrane, and C₆₀, the attractive dispersion interaction can have a greater impact on stereochemistry than the repulsive steric effect, making the compact isomer the more stable one. In particular, for the double C₆₀ adduct of pentacene 1 , the syn isomer should be the main product instead of the anti one inferred in the original synthesis experiment (Y. Murata et al., J. Org. Chem.­ 1999 , 64, 3483). With and without dispersion interactions taken into account, the Gibbs energy difference ΔG(syn?anti) is ?6.36 and +1.15 kcal mol^?1, respectively. This study reminds us that dispersion interactions as well as electrostatic or hyperconjugation effects, etc. can lead to some unusual stereochemical phenomena.     

Phenothiazine–BODIPY–Fullerene Triads as Photosynthetic Reaction Center Models: Substitution and Solvent Polarity Effects on Photoinduced Charge Separation and Recombination

Novel photosynthetic reaction center model compounds of the type donor₂–donor₁–acceptor, composed of phenothiazine, BF₂‐chelated dipyrromethene (BODIPY), and fullerene, respectively, have been newly synthesized using multistep synthetic methods. X‐ray structures of three of the phenothiazine‐BODIPY intermediate compounds have been solved to visualize the substitution effect caused by the phenothiazine on the BODIPY macrocycle. Optical absorption and emission, computational, and differential pulse voltammetry studies were systematically performed to establish the molecular integrity of the triads. The N‐substituted phenothiazine was found to be easier to oxidize by 60 mV compared to the C‐substituted analogue. The geometry and electronic structures were obtained by B3LYP/6‐31G(dp) calculations (for H, B, N, and O) and B3LYP/6‐31G(df) calculations (for S) in vacuum, followed by a single‐point calculation in benzonitrile utilizing the polarizable continuum model (PCM). The HOMO?1, HOMO, and LUMO were, respectively, on the BODIPY, phenothiazine and fullerene entities, which agreed well with the site of electron transfer determined from electrochemical studies. The energy‐level diagram deduced from these data helped in elucidating the mechanistic details of the photochemical events. Excitation of BODIPY resulted in ultrafast electron transfer to produce PTZ–BODIPY^.+–C₆₀^.?; subsequent hole shift resulted in PTZ^.+–BODIPY–C₆₀^.? charge‐separated species. The return of the charge‐separated species was found to be solvent dependent. In nonpolar solvents the PTZ^.+–BODIPY–C₆₀^.? species populated the ³C₆₀* prior to returning to the ground state, while in polar solvent no such process was observed due to relative positioning of the energy levels. The ¹BODIPY* generated radical ion‐pair in these triads persisted for few nanoseconds due to electron transfer/hole‐shift mechanism.     

High‐Potential Perfluorinated Phthalocyanine–Fullerene Dyads for Generation of High‐Energy Charge‐Separated States: Formation and Photoinduced Electron‐Transfer Studies

High oxidation potential perfluorinated zinc phthalocyanines (ZnF_nPcs) are synthesised and their spectroscopic, redox, and light‐induced electron‐transfer properties investigated systematically by forming donor–acceptor dyads through metal–ligand axial coordination of fullerene (C₆₀) derivatives. Absorption and fluorescence spectral studies reveal efficient binding of the pyridine‐ (Py) and phenylimidazole‐functionalised fullerene (C₆₀Im) derivatives to the zinc centre of the F_nPcs. The determined binding constants, K, in o‐dichlorobenzene for the 1:1 complexes are in the order of 10⁴ to 10⁵ M ^?1; nearly an order of magnitude higher than that observed for the dyad formed from zinc phthalocyanine (ZnPc) lacking fluorine substituents. The geometry and electronic structure of the dyads are determined by using the B3LYP/6‐31G* method. The HOMO and LUMO levels are located on the Pc and C₆₀ entities, respectively; this suggests the formation of ZnF_nPc^.+–C₆₀Im^.? and ZnF_nPc^.+–C₆₀Py^.? (n=0, 8 or 16) intra‐supramolecular charge‐separated states during electron transfer. Electrochemical studies on the ZnPc–C₆₀ dyads enable accurate determination of their oxidation and reduction potentials and the energy of the charge‐separated states. The energy of the charge‐separated state for dyads composed of ZnF_nPc is higher than that of normal ZnPc–C₆₀ dyads and reveals their significance in harvesting higher amounts of light energy. Evidence for charge separation in the dyads is secured from femtosecond transient absorption studies in nonpolar toluene. Kinetic evaluation of the cation and anion radical ion peaks reveals ultrafast charge separation and charge recombination in dyads composed of perfluorinated phthalocyanine and fullerene; this implies their significance in solar‐energy harvesting and optoelectronic device building applications.     

Theoretical Study on Experimentally Detected Sc2S@C84

Sc₂S@C₈₄ has recently been detected but not structurally characterized. 1 Density functional theory calculations on C₈₄ and Sc₂S@C₈₄ show that the favored isomer of Sc₂S@C₈₄ shares the same parent cage as Sc₂C₂@C₈₄, whereas Sc₂S@C₈₄:51383, which violates the isolated‐pentagon rule, is the second lowest energy isomer with the widest HOMO–LUMO gap and shows high kinetic stability. The analysis shows that Sc₂S@C₈₄:51575 is favored when the temperature exceeds 2 800 K and it can transform into the most favorable isomer Sc₂S@C₈₄:51591. Molecular orbital analysis indicates that both Sc₂S and Sc₂C₂ formally transfer four electrons to the cage, and quantum theory of atoms in molecules analysis demonstrates that there is a covalent interaction between Sc₂S and C₈₄:51591. The IR spectra of Sc₂S@C₈₄ are provided to aid future structural identification.     

New Conjugated Molecules with Two and Three Dithienyldiketopyrrolopyrrole (DPP) Moieties Substituted at meta Positions of Benzene toward p‐ and n‐Type Organic Photovoltaic Materials

Two conjugated molecules, TADPP3 and TADPP2‐TT , are reported, in which three and two dithienyldiketopyrrolopyrrole (DPP) moieties, respectively, are substituted at the meta positions of benzene. Based on cyclic voltammetry and absorption data, TADPP3 and TADPP2‐TT possess similar HOMO and LUMO energies of about ?5.2 and ?3.4 eV, respectively. Thin films of TADPP3 and TADPP2‐TT exhibit p‐type semiconducting behavior with hole mobilities of 2.36×10^?3 and 3.76×10^?4 cm² V^?1 s^?1 after thermal annealing. Molecules TADPP3 and TADPP2‐TT were utilized as p‐type photovoltaic materials to fabricate organic solar cells after blending with phenyl C₇₁ butyric acid methyl ester ( PC₇₁BM ) and phenyl C₆₁ butyric acid methyl ester ( PC₆₁BM ). The relatively low J_SC and fill factor values can be attributed to poor film morphologies based on AFM and XRD studies. A solar cell with a thin film of TADPP3 with PC₇₁BM in a weight ratio of 1:2 exhibits a high open‐circuit voltage (V_OC) of 0.99 V and a power conversion efficiency (PCE) of 2.47 %. Interestingly, TADPP3 can also be employed as an n‐type photovoltaic material. The blended thin film of TADPP3 with P3HT in a weight ratio of 1:2 gave a high V_OC of 1.11 V and a PCE of 1.08 % after thermal annealing.     

High Degree of Polymerization in a Fullerene‐Containing Supramolecular Polymer

Supramolecular polymers based on dispersion forces typically show lower molecular weights (MW) than those based on hydrogen bonding or metal–ligand coordination. We present the synthesis and self‐assembling properties of a monomer featuring two complementary units, a C₆₀ derivative and an exTTF‐based macrocycle, that interact mainly through π–π, charge‐transfer, and van der Waals interactions. Thanks to the preorganization in the host part, a remarkable log K_a=5.1±0.5 in CHCl₃ at room temperature is determined for the host–guest couple. In accordance with the large binding constant, the monomer self‐assembles in the gas phase, in solution, and in the solid state to form linear supramolecular polymers with a very high degree of polymerization. A MW above 150 kDa has been found experimentally in solution, while in the solid state the monomer forms extraordinarily long, straight, and uniform fibers with lengths reaching several microns.     

Selective Host–Guest Interactions of a Transformable Coordination Capsule/Tube with Fullerenes

An M₂L₄ coordination capsule or an M₂L₂ coordination tube was selectively formed by the combination of Hg^II hinges and bent bispyridine ligands. The two structures reversibly interconvert at room temperature in response to modulation of the metal‐to‐ligand ratio and exhibit different host–guest interaction behavior. The capsule alone encapsulates large spherical molecules, fullerenes C₆₀ and C₇₀, and the bound guests are released upon capsule‐to‐tube transformation by the simple addition of metal ions.     

Synthesis of Long‐Sought C66 with Exohedral Stabilization

Previously reported fused‐pentagon fullerenes stabilized by exohedral derivatization do not share the same cage with those stabilized by endohedral encapsulation. Herein we report the crystallographic identification of ^#4348C₆₆Cl₁₀, which has the same cage as that of previously reported Sc₂@C₆₆. According to the geometrical data of ^#4348C₆₆Cl₁₀, both strain relief (at the fused pentagons) and local aromaticity (on the remaining sp²‐hybrided carbon framework) contribute to the exohedral stabilization of this long‐sought 66 carbon atom cage.     

Electrical conductivity,impedance, and percolation behavior of carbon nanofiber and carbon nanotube containing gellan gum hydrogels

The electrical impedance behavior of gellan gum (GG), GG–carbon nanotube, and GG–carbon nanofiber hydrogel composites is reported. It is demonstrated that the impedance behavior of these gels can be modeled using a Warburg element in series with a resistor. Sonolysis (required to disperse the carbon fillers) does not affect GG hydrogel electrical conductivity (1.2 ± 0.1 mS/cm), but has a detrimental effect on the gel's mechanical characteristics. It was found that the electrical conductivity (evaluated using impedance analysis) increases with increasing volume fraction of the carbon fillers and decreasing water content. For example, carbon nanotube containing hydrogels exhibited a six‐ to sevenfold increase in electrical conductivity (to 7 ± 2 mS/cm) at water content of 82%. It is demonstrated that at water content of 95 ± 2% the electrical behavior of multiwalled nanotube containing hydrogels transitions (percolates) from transport dominated by ions (owing to GG) to transport dominated by electrons (owing to the carbon nanotube network). © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 864–871