Naohiko Ikuma

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.

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.

Paramagnetic FLCs Containing an Organic Radical Component

We have prepared new all-organic ferroelectric liquid crystalline materials containing a polar and dichiral cyclic-nitroxide unit within the rigid core. These compounds show distinct ferroelectricity in SmC* phases. The spontaneous polarization (Ps) has been measured by the triangular wave method and the tilt angle has been determined by polarizing microscopy. The relationship between the Ps and the molecular structure has been investigated by the MO calculations. The tilt angles, which are estimated from the layer distances of the SmC* phases determined by X-ray diffraction data and the molecular lengths calculated by the MO calculations, are consistent with those by polarizing microscopy.

Unusual intermolecular magnetic interaction observed in an all-organic radical liquid crystal

Here we show the first observation of an unusual intermolecular magnetic interaction in the liquid-crystalline (LC) state of an all-organic radical compound at 73 °C on water; the magnetic interaction actually allows the LC droplet on water to be attracted by a weak permanent magnet, whereas the crystalline phase did not respond to the magnet.

Paramagnetic all-organic chiral liquid crystals

A series of prototypic, paramagnetic all-organic liquid-crystalline (LC) compounds containing a chiral nitroxide unit as a spin source in the mesogen core have been prepared. Their unique electric and magnetic properties in their rod-like LC phases are summarized.

Magnetic-field-induced molecular alignment in an achiral liquid crystal spin-labeled by a nitroxyl group in the mesogen core

Here we show magnetic-field-induced molecular alignment in the achiral nematic and smectic C phases of an all-organic radical compound (1) by variable-temperature electron paramagnetic resonance (EPR) spectroscopy at a magnetic field of 0.33 T and by polarized optical microscopy (POM) observation under variable magnetic fields (0–5.0 T).

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.

Synthesis and Characterization of Novel Radical Liquid Crystals Showing Ferroelectricity

Preparation and characterization of a new series of all-organic ferroelectric liquid crystalline (LC) materials, 4-alkoxyphenyl trans-4-[5-(4-alkoxyphenyl)-2,5-dimethylpyrrolidine-1-oxyl-2-yl] benzoates (2), which are the structural isomers of the previously reported trans-2-alkoxyphenyl-5-[4-(4-alkoxybenzenecarbonyloxy)phenyl]-2,5-dimethylpyrrolidine-1-oxyls (1) containing a polar and chiral cyclic-nitroxide unit within the rigid core, are described. (2S,5S)- 2 showed ferroelectricity in the SmC* phase, and one of them exhibited a temperature-dependent spontaneous polarization (P S ) inversion, which was not observed for (2S,5S)- 1.

Synthesis and Characterization of Novel All-Organic Liquid Crystalline Radicals

We have synthesized a new series of all-organic liquid crystalline (LC) radical compounds (2), which are the structural isomers of the previously reported series (1) containing a chiral nitroxide unit in the mesogen core. Only difference between the two isomers is the orientation in the ester functionality (‒OCO‒ vs ‒COO‒). The new LC compounds 2 with C4 to C8 alkoxy terminal chains showed the distinct odd-even effects of alkoxy terminal chains with respect to the thermal stability of nematic phases, while such effects were not observed for the isomers 1.

Synthesis of a lithium-encapsulated fullerenol and the effect of the internal lithium cation on its aggregation behavior

AbstractA lithium-encapsulated fullerenol Li@C60(OH)18, as an example of a polar solvent-soluble endohedral fullerene derivative, has been synthesized and fully characterized by infrared spectroscopy, nuclear magnetic resonance spectroscopy, UV spectroscopy, electron spin resonance (ESR) spectroscopy, matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF-MS), elemental analysis, thermogravimetric analysis, and inductively coupled plasma-atomic emission spectroscopy (ICP-AES), and the particle size was determined using the induced grating (IG) method, and scanning probe microscopy. The encapsulated Li+ was clearly detected by 7Li NMR at very high field in the range −15 to −19 ppm, an intermediate lithium-encapsulated fullerenol was detected by MALDI-TOF-MS, and the molar ratio of lithium-encapsulated fullerenol to empty fullerenol was quantitatively determined to be 12:88 by ICP-AES. The solid-state ESR and particle size measurements using the IG method showed the characteristic anionic behavior with no external counter cations, in what can be called a “cation-encapsulated anion nanoparticle”, revealing the drastic differences between its properties and those of empty C60(OH)16.