Double-σ-Bonded Close-Shell Dimers and Peroxy-Linked Open-Shell Dimer Derived from a C3 Symmetric Trioxophenalenyl Neutral Diradical.

A novel neutral diradical of π-extended phenalenyl derivative having three oxo-groups, tri-tert-butyl-1,4,7-trioxophenalenyl, and two types of the corresponding σ-dimers were investigated. Quantum chemical calculations showed that the neutral diradical is in triplet ground state having doubly degenerate singly occupied molecular orbitals. The neutral diradical undergoes a σ-dimerization, generating two types of σ-dimers immediately after the preparation. One of the σ-dimers, which was selectively generated in the crystalline state, was a close-shell dimer linked through double-σ-bonds on the phenalenyl skeleton with a long C-C bond length of 1.66 Å. The other σ-dimer, which existed only in the solution state, was a peroxy-linked open-shell dimer in which one σ-bond was formed between two oxygen atoms. Furthermore, the temperature-dependent 1 H NMR and ESR spectra revealed that these σ-dimers are in equilibrium in the solution state by the reversible σ-bond formation/cleavage via the neutral diradical as a key intermediate.

Physiological and Psychological Effects of Volatile Organic Compounds from Dried Common Rush (Juncus effusus L. var. decipiens Buchen.) on Humans.

This study compared the participants' physiological responses and subjective evaluations of air scented with different concentrations of common rush (Juncus effusus L. var. decipiens Buchen.) (30 g and 15 g, with fresh air as a control). We asked 20 participants to complete a series of visual discrimination tasks while inhaling two different air samples. We evaluated (1) brain activity, (2) autonomic nervous activity, and (3) blood pressure and pulse rate, (4) in combination with self-evaluation. In addition, we quantified the concentrations of volatile organic compounds. The participants reported the scent to be sour, pungent, and smelly; this impression was likely caused by hexanal and acetic acid. Although the self-evaluations showed that participants did not enjoy the scent, their alpha amplitudes of electroencephalogram and parasympathetic nervous activity were increased, suggesting that participants were relaxed in this atmosphere. Moreover, a lower concentration resulted in a greater induction of relaxation. While the air was not pleasant-smelling, the volatile organic compounds present had a positive psychophysiological impact.

Design and Synthesis of a C3 Symmetrical Phenalenyl Derivative with Three Oxo Groups by Regioselective Deoxygenation/Oxygenation.

Tri-tert-butylated 4,7-dihydroxyphenalenone was designed and synthesized from a corresponding 4,9-dimethoxyphenalenone derivative by regioselective deoxygenation/oxygenation. The 4,7-dihydroxyphenalenone derivative showed a chromic behavior accompanied by protonation and deprotonation, giving monocation and dianion species, respectively, and their C3 symmetric electronic structures were elucidated by experimental and theoretical methods.

Room temperature hyperpolarization of nuclear spins in bulk.

Dynamic nuclear polarization (DNP), a means of transferring spin polarization from electrons to nuclei, can enhance the nuclear spin polarization (hence the NMR sensitivity) in bulk materials at most 660 times for (1)H spins, using electron spins in thermal equilibrium as polarizing agents. By using electron spins in photo-excited triplet states instead, DNP can overcome the above limit. We demonstrate a (1)H spin polarization of 34%, which gives an enhancement factor of 250,000 in 0.40 T, while maintaining a bulk sample (∼ 0.6 mg, ∼ 0.7 × 0.7 × 1 mm(3)) containing >10(19) (1)H spins at room temperature. Room temperature hyperpolarization achieved with DNP using photo-excited triplet electrons has potentials to be applied to a wide range of fields, including NMR spectroscopy and MRI as well as fundamental physics.

Hydrogen-bonding effect on spin-center transfer of tetrathiafulvalene-linked 6-oxophenalenoxyl evaluated using temperature-dependent cyclic voltammetry and theoretical calculations.

The stable tetrathiafulvalene (TTF)-linked 6-oxophenalenoxyl neutral radical exhibits a spin-center transfer with a continuous color change in solution caused by an intramolecular electron transfer, which is dependent on solvent and temperature. Cyclic voltammetry measurements showed that addition of 2,2,2-trifluoroethanol (TFE) to a benzonitrile solution of the neutral radical induces a redox potential shift that is favorable for the spin-center transfer. Temperature-dependent cyclic voltammetry of the neutral radical using a novel low-temperature electrochemical cell demonstrated that the redox potentials change with decreasing temperature in a 199:1 CH2Cl2/TFE mixed solvent. Furthermore, theoretical calculation revealed that the energy levels of the frontier molecular orbitals involved in the spin-center transfer are lowered by the hydrogen-bonding interaction of TFE with the neutral radical. These results indicate that the hydrogen-bonding effect is a key factor for the occurrence of the spin-center transfer of TTF-linked 6-oxophenalenoxyl.

Control of Exchange Interactions in π Dimers of 6-Oxophenalenoxyl Neutral π Radicals: Spin-Density Distributions and Multicentered-Two-Electron Bonding Governed by Topological Symmetry and Substitution at the 8-Position.

The tri-tert-butylphenalenyl (TBPLY) radical exists as a π dimer in the crystal form with perfect overlapping of the singly occupied molecular orbitals (SOMOs) causing strong antiferromagnetic exchange interactions. 2,5-Di-tert-butyl-6-oxophenalenoxyl (6OPO) is a phenalenyl-based air-stable neutral π radical with extensive spin delocalization and is a counter analogue of phenalenyl in terms of the topological symmetry of the spin density distribution. X-ray crystal structure analyses showed that 8-tert-butyl- and 8-(p-XC6H4)-6OPOs (X=I, Br) also form π dimers in the crystalline state. The π-dimeric structure of 8-tert-butyl-6OPO is seemingly similar to that of TBPLY even though its SOMO-SOMO overlap is small compared with that of TBPLY. The 8-(p-XC6H4) derivatives form slipped stacking π dimers in which the SOMO-SOMO overlaps are greater than in 8-tert-butyl-6OPO, but still smaller than in TBPLY. The solid-state electronic spectra of the 6OPO derivatives show much weaker intradimer charge-transfer bands, and SQUID measurements for 8-(p-BrC6H4)-6OPO show a weak antiferromagnetic exchange interaction in the π dimer. These results demonstrate that the control of the spin distribution patterns of the phenalenyl skeleton switches the mode of exchange interaction within the phenalenyl-based π dimer. The formation of the relevant multicenter-two-electron bonds is discussed.

A dicyanomethylene-substituted triangulene: effects of molecular-symmetry reduction and electron-accepting substituents on a fused polycyclic neutral π-radical system.

A triangulene-based C2-symmetric 33 π-conjugated stable neutral π-radical, 2(·), which possesses two dicyanomethylene groups and one oxo group, has been designed, synthesized, and isolated as an analogue of tris(dicyanomethylene) derivative 1(·) and trioxo derivative TOT(·) with C3 symmetry. Effects of molecular-symmetry reduction and electron-accepting substituents on this fused polycyclic neutral π-radical system were studied in terms of their molecular structure, electronic-spin structure, and electrochemical and optical properties with the help of theoretical calculations. Interestingly, this system (2(·)) has a four-stage redox ability, like TOT(·), as well as low frontier energy levels and a small SOMO-LUMO gap, similar to 1(·), in spite of the loss of the degenerate LUMOs in symmetry-lowered 2(·), which is associated with the attachment of the weaker electron-accepting oxo group instead of the dicyanomethylene group in 1(·). These prominent results are attributable to the structural and electronic properties in the triangulene-based highly delocalized fused polycyclic neutral π-radical system.

Organic rechargeable batteries with tailored voltage and cycle performance.

Made to order: Rechargeable batteries are fabricated by using organic electron acceptors and donors as active cathode materials. Their output voltage and cycle performance can be tuned by organic chemistry techniques. The output voltages are linked to both the redox potentials and the energy levels of the frontier molecular orbitals of the cathode materials, enabling to predict the output voltage at an early stage of the design.

An extremely redox-active air-stable neutral π radical: dicyanomethylene-substituted triangulene with a threefold symmetry.

Radically active: A redox-active air-stable neutral π radical (1(·)) with three dicyanomethylene groups introduced with threefold symmetry into a triangulene π skeleton instead of the oxygen atoms of TOT(·) was designed, synthesized, and characterized (see figure). The enhanced electron-accepting ability and extended π-electronic system of this chemical modification gave an extremely small SOMO-LUMO gap and significantly lowered the frontier orbital energies, leading to the remarkable increase in the redox stages.

A synthetic two-spin quantum bit: g-engineered exchange-coupled biradical designed for controlled-NOT gate operations.

A quantum gate: A system of two coupled electron spins that is useful for simple quantum computing operations has been prepared by synthesis of a biradical 1 and co-crystallization with an isomorphous host molecule. The two weakly exchange-coupled quantum bits (target qubit blue and control qubit red) span four electron spin states. The electron spin transition is denoted by two black arrows.

Pulsed electron spin nutation spectroscopy of weakly exchange-coupled biradicals: a general theoretical approach and determination of the spin dipolar interaction.

Weakly exchange-coupled biradicals have attracted much attention in terms of their DNP application in NMR spectroscopy for biological systems or the use of synthetic electron-spin qubits. Pulse-ESR based electron spin nutation (ESN) spectroscopy applied to biradicals is generally treated as transition moment spectroscopy from the theoretical side, illustrating that it is a powerful and facile tool to determine relatively short distances between weakly exchange-coupled electron spins. The nutation frequency as a function of the microwave irradiation strength ω(1) (angular frequency) for any cases of weakly exchange-coupled systems can be classified into three categories; D(12) (spin dipolar interaction)-driven, Δg-driven and ω(1)-driven nutation behaviour with the increasing strength of ω(1). For hetero-spin biradicals, Δg effects can be a dominating characteristic in the biradical nutation spectroscopy. Two-dimensional pulse-based electron spin nutation (2D-ESN) spectroscopy operating at the X-band can afford to determine small values of D(12) in weakly exchange-coupled biradicals in rigid glasses. The analytical expressions derived here for ω(1)-dependent nutation frequencies are based on only four electronic spin states relevant to the biradicals, while real biradical systems often have sizable hyperfine interactions. Thus, we have evaluated nuclear hyperfine effects on the nutation frequencies to check the validity of the present theoretical treatment. The experimental spin dipolar coupling of a typical TEMPO-based biradical 1, (2,2,6,6-tetra[((2)H(3))methyl]-[3,3-(2)H(2),4-(2)H(1),5,5-(2)H(2)]piperidin-N-oxyl-4-yl)(2,2,6,6-tetra[((2)H(3))methyl]-[3,3-(2)H(2),4-(2)H(1),5,5-(2)H(2),(15)N]piperidin-(15)N-oxyl-4-yl) terephthalate in a toluene glass, with a distance of 1.69 nm between the two spin sites is D(12) = -32 MHz (the effect of the exchange coupling J(12) is vanishing due to the homo-spin sites of 1, i.e.Δg = 0), while 0 < |J(12)|≦ 1.0 MHz as determined by simulating the random-orientation CW ESR spectra of 1. In addition, we have carried out Q-band pulsed ELDOR (ELectron-electron DOuble Resonance) experiments to confirm whether the obtained values for D(12) and J(12) are accurate. The distance is in a fuzzy region for the distance-measurements capability of the conventional, powerful ELDOR spectroscopy. The strong and weak points of the ESN spectroscopy with a single microwave frequency applicable to weakly exchange-coupled multi-electron systems are discussed in comparison with conventional ELDOR spectroscopy. The theoretical spin dipolar tensor and exchange interaction of the TEMPO biradical, as obtained by sophisticated quantum chemical calculations, agree with the experimental ones.

Organic tailored batteries materials using stable open-shell molecules with degenerate frontier orbitals.

Secondary batteries using organic electrode-active materials promise to surpass present Li-ion batteries in terms of safety and resource price. The use of organic polymers for cathode-active materials has already achieved a high voltage and cycle performance comparable to those of Li-ion batteries. It is therefore timely to develop approaches for high-capacity organic materials-based battery applications. Here we demonstrate organic tailored batteries with high capacity by using organic molecules with degenerate molecular orbitals (MOs) as electrode-active materials. Trioxotriangulene (TOT), an organic open-shell molecule, with a singly occupied MO (SOMO) and two degenerate lowest-unoccupied MOs (LUMOs) was investigated. A tri-tert-butylated derivative ((t-Bu)(3)TOT)exhibited a high discharge capacity of more than 300 A h kg(-1), exceeding those delivered by Li-ion batteries. A tribrominated derivative (Br(3)TOT) was also shown to increase the output voltage and cycle performance up to 85% after 100 cycles of the charge-discharge processes.

Electronic stabilization effect of a spin-delocalized neutral radical: synthesis of an 8-cyano-6-oxophenalenoxyl derivative and quantitative evaluation of the electronic spin structure in terms of resonance structures.

A new 2,5-di-tert-butyl-6-oxophenalenoxyl (6OPO) derivative with a cyano group at the 8-position, where a large spin density resides, has been synthesized. This neutral radical exhibits high stability in the solid state in air despite the low steric protection on the 8-position; the stability is comparable to that of a corresponding 8-tert-butylated 6OPO derivative. EPR/(1)H-ENDOR/TRIPLE (electron paramagnetic resonance/(1)H-electron-nuclear double resonance/TRIPLE) spectroscopy and cyclic voltammetry showed an extended spin delocalization on the cyano group and a significant increase in electron-accepting ability relative to that of the 8-tert-butylated 6OPO derivative. DFT calculations indicated the extension of a singly occupied molecular orbital (SOMO) onto the cyano group and the lower-lying SOMO and LUMO in comparison with those of the 8-tert-butylated 6OPO derivative, which was consistent with experimental results. Furthermore, the extended nature of π conjugation onto the cyano group was quantitatively evaluated by calculating the contributing weights of resonance structures in terms of a molecular orbital (MO)-based valence-bond (VB) method. Herein, the synthesis and physical properties of the 8-cyano-6OPO derivative are described, emphasizing that the high stability arises from the electronic effect of the cyano group. Also, the usefulness of the quantitative resonance structure analysis is shown.

Curve-structured phenalenyl chemistry: synthesis, electronic structure, and bowl-inversion barrier of a phenalenyl-fused corannulene anion.

We have demonstrated the features of curve-structured phenalenyl chemistry, for the first time. A phenalenyl-fused corannulene anion has been designed by the annelation of a six-memberd ring across peri-positions of corannulene and generated as a stable species in a degassed solution. The 1H and 13C NMR spectra have shown the highly symmetrical structure and high-field shifts of protons and carbons at the asterisked positions in the chemical structure, indicating the occurrence of large negative charge densities at these positions. These results well agree with the HOMO picture and the electrostatic potential surface, demonstrating the phenalenyl anion-type electronic structure is retained in the curved-surface pi-system. The calculated bowl-inversion barrier of the anion (11.3 kcal/mol) is larger than that of corannulene (9.2 kcal/mol) because of peri-annelation of the corannulene skeleton. The calculations of the barriers of the neutral radical (12.6 kcal/mol), radical dianion (8.1 kcal/mol), and trianion (5.4 kcal/mol) of the phenalenyl-fused corannulene have exhibited a stepwise flattening of the curvature with increase in negative charge. Therefore, we have revealed that the bowl-inversion barrier of the anion is governed by the setoff of the peri-annelation and negative charge effects.

The first bowl-shaped stable neutral radical with a corannulene system: synthesis and characterization of the electronic structure.

[structure: see text] A bowl-shaped neutral radical with a corannulene system has been designed and synthesized for the first time as a stable solid in air. An unequivocal characterization of the electronic properties of the radical shows that an appreciable amount of spin delocalization extends onto the corannulene unit's curved surface.

Redox-based spin diversity in a 6-oxophenalenoxyl system: generation, ESR/ENDOR/TRIPLE, and theoretical studies of 2,5,8-tri-tert-butylphenalenyl- 1,6-bis(olate) salts.

[reaction: see text] Novel open-shell molecular salts, 2,5,8-tri-tert-butylphenalenyl-1,6-bis(olate) salts, were designed on the basis of the 6-oxophenalenoxyl system and generated by the chemical reduction of 6-hydroxyphenalenone derivatives. ESR/ENDOR/TRIPLE measurements and DFT calculations provide unequivocal determination of the structure and spin density distribution, which demonstrate redox-based spin diversity of the 6-oxophenalenoxyl system.