Regioselective addition of Grignard reagents to tosylazafulleroid and derivatization to 1,2-disubstituted [60]fullerene.

Grignard reagents (RMgBr: R = Et, p-tolyl) selectively attacked the ß-position of the bridgehead double bond of tosylazafulleroid through interaction of Mg with the S[double bond, length as m-dash]O group. The following [5,6] ring closure and C-N bond scission led to aryl/alkyl aminylfullerenes with 1,2-configuration. Tolyl-substituted aminylfullerene was further converted into 1,4-di(p-tolyl)fullerene on treatment in acidic toluene.

Electrochemical reduction of cationic Li+@C60 to neutral Li+@C60˙-: isolation and characterisation of endohedral [60]fulleride.

Lithium-encapsulated [60]fullerene Li@C60, namely, lithium-ion-encapsulated [60]fullerene radical anion Li+@C60˙-, was synthesised by electrochemical reduction of lithium-ion-encapsulated [60]fullerene trifluoromethanesulfonylimide salt [Li+@C60](TFSI-). The product was fully characterised by UV-vis-NIR absorption and ESR spectroscopy as well as single-crystal X-ray analysis for the co-crystal with nickel octaethylporphyrin. In solution Li@C60 exists as a monomer form dominantly, while in the crystal state it forms a dimer (Li@C60-Li@C60) through coupling of the C60 radical anion cage. These structural features were supported by DFT calculations at the M06-2X/6-31G(d) level of theory.

Preparation, characterization and magnetic behavior of a spin-labelled physical hydrogel containing a chiral cyclic nitroxide radical unit fixed inside the gelator molecule.

An optically active amphiphilic nitroxide radical compound [(S,S,R)-], which contains a paramagnetic (2S,5S)-2,5-dimethyl-2,5-diphenylpyrrolidine-N-oxyl radical group fixed in the inner position together with a hydrophobic long alkyl chain and a hydrophilic (R)-alanine residue in the opposite terminal positions, was found to serve as a low-molecular-weight gelator in H2O to give rise to a spin-labelled physical hydrogel. Characterization of the hydrogel was performed by microscopic (SEM, TEM and AFM) techniques, XRD and SAXS measurements, and IR, UV and CD spectroscopies. The gel-sol transition temperature was determined by EPR spectral line-width (ΔHpp) analysis. Measurement of the temperature dependence of relative paramagnetic susceptibility (χrel) for the hydrogel and sol phases was achieved by means of the double-integration of VT-EPR spectra.

Hetero Bis-Addition of Spiro-Acetalized or Cyclohexanone Ring to 58π Fullerene Impacts Solubility and Mobility Balance in Polymer Solar Cells.

Fullerene bis-adducts are increasingly being studied to gain a high open circuit voltage (Voc) in bulk heterojunction organic photovoltaics (OPVs). We designed and synthesized homo and hetero bis-adduct [60]fullerenes by combining fused cyclohexanone or a five-membered spiro-acetalized unit (SAF5) with 1,2-dihydromethano (CH2), indene, or [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). These new eight 56π fullerenes showed a rational rise of the lowest unoccupied molecular orbital (LUMO). We perform a systematic study on the electrochemical property, solubility, morphology, and space-charge-limited current (SCLC) mobility. The best power conversion efficiency (PCE) of 4.43% (average, 4.36%) with the Voc of 0.80 V was obtained for poly(3-hexylthiophene) (P3HT) blended with SAF5/indene hetero bis-adduct, which is a marked advancement in PCE compared to the 0.9% of SAF5 monoadduct. More importantly, we elucidate an important role of mobility balance between hole and electron that correlates with the device PCEs. Besides, an empirical equation to extrapolate the solubilities of hetero bis-adducts is proposed on the basis of those of counter monoadducts. Our work offers a guide to mitigate barriers for exploring a large number of hetero bis-adduct fullerenes for efficient OPVs.

Oxidative deamination of azafulleroids into C60 by peracids.

Oxidation of azafulleroids with peracids regenerated C60 depending on the N-substituents. Alkyl-substituted azafulleroids preferred the oxidation of nitrogen to afford N-oxides as possible intermediates for C60 in moderate yields. Phenyl- and tosyl-substituted azafulleroids rather allowed the oxidation at the carbon cage. Theoretical calculations predicted the order of reactivity of azafulleroids as well as the relative N/C nucleophilicity.

Stereochemistry of spiro-acetalized [60]fullerenes: how the exo and endo stereoisomers influence organic solar cell performance.

Exploiting bis-addition products of fullerenes is a rational way to improve the efficiency of bulk heterojunction-type organic photovoltaic cells (OPV); however, this design inherently produces regio- and stereoisomers that may impair the ultimate performance and fabrication reproducibility. Here, we report unprecedented exo and endo stereoisomers of the spiro-acetalized [60]fullerene monoadduct with methyl- or phenyl-substituted 1,3-dioxane (SAF6). Although there is no chiral carbon in either the reagent or the fullerene, equatorial (eq) rather than axial (ax) isomers are selectively produced at an exo-eq:endo-eq ratio of approximately 1:1 and can be easily separated using silica gel column chromatography. Nuclear Overhauser effect measurements identified the conformations of the straight exo isomer and bent endo isomer. We discuss the origin of stereoselectivity, the anomeric effect, intermolecular ordering in the film state, and the performance of poly(3-hexylthiophene):substituted SAF6 OPV devices. Despite their identical optical and electrochemical properties, their solubilities and space-charge limited current mobilities are largely influenced by the stereoisomers, which leads to variation in the OPV efficiency. This study emphasizes the importance of fullerene stereochemistry for understanding the relationship between stereochemical structures and device output.

Dramatic mechanistic change in acid-catalyzed arylation of azafulleroids depending on their ambident N/C basicity: formation of cyclopentene centered pentakisadduct.

Azafulleroid, amino-bridged [5,6]-open fullerene, has the ambident N/C basicity of the incorporated enamine moiety. Acid-catalyzed arylation of N-substituted azafulleroids proceeded via two types of initial N/C protonation to perform monoarylation or 1,4-bisarylation for the N-alkyl substituents and shuttlecock-type pentakisarylation for the N-phenyl substituent. The dramatic product change was explained by considering the possible mechanism as well as the DFT computational results.

Kinetic study of the Diels-Alder reaction of Li⁺@C60 with cyclohexadiene: greatly increased reaction rate by encapsulated Li⁺.

We studied the kinetics of the Diels-Alder reaction of Li(+)-encapsulated [60]fullerene with 1,3-cyclohexadiene and characterized the obtained product, [Li(+)@C60(C6H8)](PF6(-)). Compared with empty C60, Li(+)@C60 reacted 2400-fold faster at 303 K, a rate enhancement that corresponds to lowering the activation energy by 24.2 kJ mol(-1). The enhanced Diels-Alder reaction rate was well explained by DFT calculation at the M06-2X/6-31G(d) level of theory considering the reactant complex with dispersion corrections. The calculated activation energies for empty C60 and Li(+)@C60 (65.2 and 43.6 kJ mol(-1), respectively) agreed fairly well with the experimentally obtained values (67.4 and 44.0 kJ mol(-1), respectively). According to the calculation, the lowering of the transition state energy by Li(+) encapsulation was associated with stabilization of the reactant complex (by 14.1 kJ mol(-1)) and the [4 + 2] product (by 5.9 kJ mol(-1)) through favorable frontier molecular orbital interactions. The encapsulated Li(+) ion catalyzed the Diels-Alder reaction by lowering the LUMO of Li(+)@C60. This is the first detailed report on the kinetics of a Diels-Alder reaction catalyzed by an encapsulated Lewis acid catalyst rather than one coordinated to a heteroatom in the dienophile.

First synthesis and aggregation behaviour of periconjugated triazoliumfullerene.

Triazoliumfullerene was first prepared by the [3+2] cycloaddition of in situ generated 1,3-diaza-2-azoniaallene with fullerene and was characterized by the dispersed positive charge over the fullerene sphere associated with periconjugation. This new type of amphiphilic fullerene tended to form vesicles and crystalline aggregates after the casting of THF or MeOH solutions.

Ionic conductivity of [Li+@C60](PF6(-)) in organic solvents and its electrochemical reduction to Li+@C60(·-).

The ionic conductivity of [Li(+)@C60](PF6(-)) was measured in o-dichlorobenzene, and found to be higher than that of TBA(+)PF6(-). Electrochemical reduction of [Li(+)@C60](PF6(-)) without any supporting electrolyte gave the monovalent radical anion Li(+)@C60˙(-), as confirmed by the characteristic ESR signal and NIR absorption band.

Synthesis of a new class of fullerene derivative Li⁺@C60O⁻(OH)7 as a "cation-encapsulated anion nanoparticle".

Metal encapsulation into a cage and chemical modification on the outer surface of fullerenes endow them with some unique characteristic properties. Although the derivatization of endohedral fullerenes holds promise for producing novel new nano-carbon materials, there are few reports about such compounds. Herein, we report the synthesis of lithium encapsulated fullerenol Li(+)@C60O(-)(OH)7 using a fuming sulfuric acid method from [Li(+)@C60](PF6(-)) and characterization of its structure by IR, NMR, FAB mass spectroscopy, and elemental analysis. The hydroxylation of [Li(+)@C60](PF6(-)) is site-selective to preferentially give a single isomer (ca. 70%) with two minor isomers in marked contrast to the reaction of empty C60. We conclude from the analysis of radical species produced in the reaction of a C60 cage with fuming sulfuric acid that this unusual site-selective hydroxylation is caused by the lower HOMO level of Li(+)@C60 than that of empty C60. Furthermore, our results clearly indicate that the internal lithium cation is interacted with the introduced hydroxyl groups, and thus the properties of endohedral fullerenes can be controlled by the external modification of a fullerene cage.

Facile and exclusive formation of aziridinofullerenes by acid-catalyzed denitrogenation of triazolinofullerenes.

Variously substituted [6,6]closed aziridinofullerenes were exclusively obtained from acid-catalyzed denitrogenation of triazolinofullerenes without formation of relevant [5,6]open azafulleroids, which are the major products on noncatalyzed denitrogenation. The mechanistic consideration by DFT calculations suggested a reaction sequence involving initial pre-equilibrium protonation of the triazoline N(1) atom, generation of aminofullerenyl cation by nitrogen-extrusion, and final aziridination.

First kinetic evidence for the CH/π and π/π solute-solvent interaction of C60 in the Diels-Alder reaction with cyclohexadiene.

The first CH/π solute-solvent interaction of C(60) was evidenced by the kinetic solvent effects in the Diels-Alder reaction with 1,3-cyclohexadiene based on the evaluation of linear free energy relationship of log k(2) with empirical solvent polarity and basicity parameters, E(T)(30) and D(π), respectively.

Thermal [2+2] cycloaddition of morpholinoenamines with C60 via a single electron transfer.

The thermal reaction of C(60) with five- and six-membered morpholinocycloalkenes in refluxing toluene exclusively gave the [2+2] cycloadducts in high yields. However, a seven-membered homologue sluggishly reacted with C(60) because of the increasing steric hindrance. This cycloaddition reaction is likely to proceed via a single electron transfer (SET), a radical-coupling, and subsequent ion cyclization rather than the prior proton transfer between the radical ions.

Anisotropic and inhomogeneous magnetic interactions observed in all-organic nitroxide radical liquid crystals.

An anisotropic and inhomogeneous magnetic interaction (the average spin-spin interaction constant (-)J > 0) was observed in the various liquid crystalline (LC) phases of racemic and nonracemic all-organic radical LC compounds 1a and 1b. We discussed how the LC superstructures induced the magnetic interaction to operate in the LC phases in terms of spin-spin dipole and exchange interactions by means of VT-EPR spectroscopy. The magnitude of the magnetic interaction depended on the type of LC phase, or the superstructure. Furthermore, these radical LC droplets floating on water were commonly attracted to a permanent magnet and moved freely under the influence of this magnet, whereas the crystallized particles of the same compounds never responded to the magnet. The response of the LC droplets to the magnet also varied depending on the type of LC phase, that is, the extent of the magnetic interaction.

Kinetics and regioselectivity in the Diels-Alder reaction of fulleroids vs. methanofullerene and C60.

Fulleroids, obtained from the 1,3-dipolar cycloaddition of fullerene with a diazoalkane, have a [5,6]-open methylene bridge and two highly twisted bridgehead double bonds. The [H,H]- and [H,CN]-substituted fulleroids were found to display significantly enhanced and regioselective Diels-Alder addition as compared with the [6,6] closed methanofullerene and C(60) with 2,3-dimethyl-1,3-butadiene, but reduced and nonregioselective addition with cyclopentadiene. NMR analysis of the 1:1 adduct and quantum calculations indicated that the high reactivity and the regioselective addition are due to pi-orbital misalignment at the bridgehead double bond.

Kinetic evidence for dihapto (eta(2)) pi-aryl participation in acid-catalyzed ring opening of diarylhomobenzoquinone epoxides.

The BF(3)-catalyzed ring-opening reaction of variously endo/exo m- and p-substituted diarylhomobenzoquinone epoxides proceeded through a transannular S(E)2-Ar cyclization of endo-aryl groups to give the tricyclic diketo-alcohols and cyclohexadienone spiro-linked tricyclic diketo-alcohols. Kinetics of these reactions has been investigated in CDCl(3) at 30 degrees C in order to elucidate the possible remote pi-aryl participation. The rates were significantly increased with increasing electron-donating ability of the endo-aryl substituents X (k(p-MeO)/k(p-CF3) = 8200) but only negligibly influenced by the distal exo-aryl substituents Y (k(p-MeO)/k(p-CF3) = 2.1). For the endo-X substituted series, an excellent linear free energy relationship, log k(rel)(endo) = -2.49sigma(ipso) - 1.62sigma(ortho) - 0.108 (R(2) = 0.98, n = 8), was attained using two modified site-dependent substituent parameters sigma(ipso) (using sigma(p)(+) for p-X and sigma(m) for m-X) and sigma(ortho) (using sigma(m) for p-X and sigma(p)(+) for m-X). This means that the dihapto(eta(2)) pi-coordination occurs in the pi-aryl participation, with the ipso pi-electron donation contributing 1.6 times more effectively than the ortho one. On the other hand, the distal exo-Y substituted series gave an acceptable Yukawa-Tsuno equation with small polar and resonance contributions; log k(rel)(exo) = -0.912(sigma(0) + 0.237Deltasigma(R)(+)) (R(2) = 0.96, n = 8). These kinetic substituent effects were compared with those of the acid-catalyzed pi-aryl assisted transannular S(E)2-Ar cyclization of the cyclobutene-fused diarylhomobenzoquinones. It was found that the geometrical characteristics of the vacant oxirane Walsh orbital and the cyclobutene antibonding orbital play a crucial role in the topological features of eta(2) pi-aryl participation.

Organic field effect transistor using pentacene single crystals grown by a liquid-phase crystallization process.

Nearly perfect pentacene single crystals with wide terraces several micrometers in width were grown by crystallization from a pentacene-containing trichlorobenzene solution. Organic field-effect transistors (OFETs) were fabricated with the pentacene single crystals and characterized for their electrical properties. The field effect mobility was found to be in the range of 0.4-0.6 cm(2)/V x s, which is comparable to that of OFETs fabricated with pentacene single crystals prepared by a physical vapor-phase growth method. The results described in this paper clearly demonstrate that the crystallization of organic semiconductors from solution is a promising chemical method for device processing of OFETs.

EPR studies on molecular orientation in a surface-stabilized paramagnetic liquid crystal cell.

By EPR spectroscopy, we have developed a new method for determining the molecular orientation in a surface-stabilized liquid crystal (LC) cell, which includes a paramagnetic LC, (2S,5S)-2,5-dimethyl-2-heptyloxyphenyl-5-[4-(4-octyloxybenzenecarbonyloxy)phenyl]pyrrolidine-1-oxy (1), whose spin source is fixed in the rigid core. For each phase of racemic [(+/-)] and enantiomerically enriched [(S,S)] 1 in a surface-stabilized LC cell (4 microm thickness), the observed g-value profiles depending on the angle between the applied magnetic field and the cell plane were successfully simulated by the orientation models: (i) the LC molecule in the nematic (N) phase of (+/-)-1 freely rotates around the long axis, which is always parallel to the rubbing direction; (ii) the long axis of the freely rotating LC molecule in the chiral nematic (N*) phase of (S,S)-1 is always parallel to the cell plane but rotates in the plane to form a helical superstructure; and (iii) in the crystalline phase of (S,S)-1, the molecular long axis forms a helical superstructure similar to that of the N* phase, but the molecule is fixed around the long axis so that the NO bond lies in the cell plane. Fitting the temperature profile of the g-value in the N phase of (+/-)-1 by use of the Haller equation, we determined the molecular g-values along the molecular long axis (g(parallelM)) and short axis (g(perpendicularM)), which were successfully reproduced by the use of the set of principal g-values of a similar nitroxide with consideration of the structure of the LC molecule optimized by Molecular Mechanics 3 (MM3).

Induction and inhibition of preferential enrichment by controlling the mode of the polymorphic transition with seed crystals.

Both induction and inhibition of "preferential enrichment", an unusual symmetry-breaking enantiomeric-resolution phenomenon observed upon simple recrystallization of a certain kind of racemic crystals from organic solvents, have been successfully achieved by controlling the mode of the polymorphic transition during crystallization with appropriate seed crystals. Such control of the polymorphic transition can be interpreted in terms of a novel phenomenon consisting of 1) the adsorption of prenucleation aggregates, 2) the heterogeneous nucleation and crystal growth of a metastable crystalline form, and 3) the subsequent polymorphic transition into the more stable form; these three processes occur on the same surface of a seed crystal. We refer to this phenomenon as an "epitaxial transition", which has been confirmed by means of in situ attenuated total reflection (ATR) FTIR spectroscopy in solution and the solid state, differential scanning calorimetry (DSC) measurements of the deposited crystals, and X-ray crystallographic analysis of the single crystals or the direct-space approach employing the Monte Carlo method with the Rietveld refinement for the structure solution from the powder X-ray diffraction data.