Michihisa Murata

Encapsulation and Dynamic Behavior of Two H2 Molecules in an Open-Cage C70

An open-cage C70 derivative having a 13-membered ring opening (2) was synthesized by a three-step reaction; thermal reaction of C70 with a pyridazine derivative, oxidative cleavage of the CC double bond, and insertion of a sulfur atom to the opening. The structure of 2 was determined by X-ray analysis. One H2 molecule was introduced into 2 to give H2@2 in 97% yield. Furthermore, two H2 molecules were encapsulated in 2 in 3% yield. The positional exchange of two H2 molecules inside 2 was clearly observed by the dynamic low-temperature NMR measurements.

Synthesis of a distinct water dimer inside fullerene C70

The water dimer is an ideal chemical species with which to study hydrogen bonds. Owing to the equilibrium between the monomer and oligomer structure, however, selective generation and separation of a genuine water dimer has not yet been achieved. Here, we report a synthetic strategy that leads to the successful encapsulation of one or two water molecules inside fullerene C70. These endohedral C70 compounds offer the opportunity to study the intrinsic properties of a single water molecule without any hydrogen bonding, as well as an isolated water dimer with a single hydrogen bond between the two molecules. The unambiguously determined off-centre position of water in (H2O)2@C70 by X-ray diffraction provides insights into the formation of (H2O)2@C70. Subsequently, the (1)H NMR spectroscopic measurements for (H2O)2@C70 confirmed the formation of a single hydrogen bond rapidly interchanging between the encapsulated water dimer. Our theoretical calculations revealed a peculiar cis-linear conformation of the dimer resulting from confinement effects inside C70.

Rational synthesis, enrichment, and (13)C NMR spectra of endohedral C(60) and C(70) encapsulating a helium atom.

Endohedral fullerenes encapsulating a helium atom, i.e., He@C(60) and He@C(70), at occupation levels of 30% were prepared by rational chemical synthesis. The existence of weak interactions between the inner helium and the outer fullerene cages was demonstrated by experimental and computational investigations.

On‐Top π‐Stacking of Quasiplanar Molecules in Hole‐Transporting Materials: Inducing Anisotropic Carrier Mobility in Amorphous Films

Dimers of partially oxygen-bridged triarylamines were designed and synthesized as hole-transporting materials. X-ray structural analyses revealed that these compounds form on-top π-stacking aggregates in the crystalline state. TRMC measurements showed that high levels of anisotropic charge transport were induced in the direction of the π-stacking. Surprisingly, even in vacuum-deposited amorphous films, these compounds retained some of the face-on π-stacking, thus facilitating an out-of-plane carrier mobility.

A Magnetic Switch for Spin-Catalyzed Interconversion of Nuclear Spin Isomers

The interconversion of ortho-hydrogen (oH(2)) and para-hydrogen (pH(2)), the two nuclear spin isomers of dihydrogen, requires a paramagnetic spin catalyst such as a nitroxide. We report the design and demonstration of spin catalysis of the interconversion of oH(2) and pH(2) incarcerated in an endofullerene based on a reversible nitroxide/hydroxylamine system. The system is an example of a reversible magnetic spin catalysis switch that can increase the rate of interconversion of the nuclear spin isomers of H(2) by a factor of approximately 10(4).

X-ray observation of a helium atom and placing a nitrogen atom inside He@C60 and He@C70.

Single crystal X-ray analysis has been used as a powerful method to determine the structure of molecules. However, crystallographic data containing helium has not been reported, owing to the difficulty in embedding helium into crystalline materials. Here we report the X-ray diffraction study of He@C60 and the clear observation of a single helium atom inside C60. In addition, the close packing of a helium atom and a nitrogen atom inside fullerenes is realized using two stepwise insertion techniques, that is, molecular surgery to synthesize the fullerenes encapsulating a helium atom, followed by nitrogen radio-frequency plasma methods to generate the fullerenes encapsulating both helium and nitrogen atoms. Electron spin resonance analysis reveals that the encapsulated helium atom has a small but detectable influence on the electronic properties of the highly reactive nitrogen atom coexisting inside the fullerene, suggesting the potential usage of helium for controlling electronic properties of reactive species.

Synthesis of open-cage ketolactam derivatives of fullerene C60 encapsulating a hydrogen molecule.

A novel open-cage fullerene C60 derivative having a bis(hemiketal) moiety was synthesized by the reaction of C60-N-MEM-ketolactam (MEM: 2-methoxyethoxymethyl) with N-methylmorpholine N-oxide in the presence of water. The structure was clearly determined by single crystal X-ray analysis. Further enlargement of the opening was performed by treatment with trifluoroacetic anhydride to give the tetraketo derivative having a 15-membered ring opening. For H2-insertion into the cage, the derivative was exposed to a high pressure of H2. After the encapsulation, the opening size was reduced to the original one while keeping the hydrogen molecule inside the cage. This compound can be a possible precursor for endohedral azafullerenes encapsulating a hydrogen molecule.

Expansion of Orifices of Open C60 Derivatives and Formation of an Open C59S Derivative by Reaction with Sulfur

The reaction of a tetraketo-open-cage C60 derivative with elemental sulfur in the presence of tetrakis(dimethylamino)ethylene afforded novel open C60 derivatives containing sulfur atom(s) in the rim of the orifice and the first example of an open C59S derivative. The single crystal X-ray analyses clearly determined these structures and demonstrated that a water molecule was encapsulated inside the cages. The orifice sizes and electronic properties of these fullerene derivatives were revealed.

Electron-Deficient Tetrabenzo-Fused Pyracylene and Conversions into Curved and Planar π-Systems Having Distinct Emission Behaviors.

Polycyclic aromatic compounds containing fully unsaturated five-membered ring(s) have been intensively studied because of their unique properties, which include high electron affinity and reactivity. Reported herein is an efficient route for the synthesis of tetrabenzo-fused pyracylene, which comprises pyracylene and tetracene segments, using intramolecular oxidative C-H coupling. It was shown to possess high electron affinity and was found to undergo addition reactions with n-butyllithium or benzyne. These reactions led to either a 1,4-addition compound or triptycene-type adduct with a curved or planar π-system, respectively. Although these compounds exhibited similar sky-blue emissions in a dilute solution, the emission band of the 1,4-addition compound was significantly red-shifted in the solid state and exhibited intense yellow emission attributable to the excimer, while the triptycene-type adduct retained the intense blue color emission in the solid state.

Synthesis and structure of an open-cage thiafullerene C69S: reactivity differences of an open-cage C70 tetraketone relative to its C60 analogue.

An open-cage C70 fullerene with a 13-membered ring-opening and a bis(hemiacetal) moiety was synthesized by the reaction of the corresponding open-cage C70 diketone with nucleophilic oxidizing agents. The size of the cage opening could be expanded by a subsequent dehydration reaction. Reaction of the thus obtained open-cage C70 tetraketone with elemental sulfur in the presence of tetrakis(dimethylamino)ethylene resulted in the formation of the first example of an open-cage C69S thiafullerene with a 12-membered ring-opening. The formation of this sulfur-containing heterofullerene reflects a significantly different chemical reactivity for the open-cage C70 tetraketone relative to its C60 analogue. The structures of all novel compounds were unambiguously determined by single crystal X-ray diffraction analyses, in addition to which the electrochemical properties of the thiafullerene C69S were examined and compared with those of the corresponding C70 analogue.