Kazuhiro Nakasuji

Alternating covalent bonding interactions in a one-dimensional chain of a phenalenyl-based singlet biradical molecule having Kekulé structures.

A novel naphthoquinoid singlet biradical (2a) stabilized by phenalenyl rings is prepared by a multistep procedure and is investigated in terms of covalent bonding interactions. The molecule 2a gives single crystals, in which a 1D chain is formed with a very short π-π contact at the overlapping phenalenyl rings. The unpaired electrons in 2a are involved in covalent bonding interactions not only within the molecule but also between the molecules in the 1D chain, and a linear conjugation is made of the alternating intra- and intermolecular covalent bonding interactions through conventional π-conjugation and multicenter bonding, respectively. The linear conjugation causes a lower-energy shift of the optical transition band in the crystal, but the transition energy is higher than that of the benzoquinoid singlet biradical (1a). This optical behavior and the magnetic susceptibility measurements reveal that the intermolecular covalent bonding interaction in the 1D chain of 2a is greater in strength than the intramolecular one, despite the fact that a fully conjugated Kekulé structure can be drawn for 2a.

Ambipolar organic field-effect transistors based on a low band gap semiconductor with balanced hole and electron mobilities

The authors have demonstrated the thin-film properties and the ambipolar transport of a delocalized singlet biradical hydrocarbon with two phenalenyl radical moieties (Ph2-IDPL). The organic field-effect transistors (OFETs) based on Ph2-IDPL exhibit ambipolar transport with balanced hole and electron mobilities in the order of 10−3cm2∕Vs. The Ph2-IDPL film is an organic semiconductor with a low band gap of 0.8eV and has small injection barriers from gold electrodes to both the highest occupied molecular orbital and the lowest unoccupied molecular orbital. A complementary metal-oxide-semiconductor-like inverter using two identical Ph2-IDPL based ambipolar OFETs shows a sharp inversion of the input voltage with high gain.

Self-organizing super-structures formed from hydrogen-bonded biimidazolate metal complexes

Manipulation of molecular crystals formed from self-organization is one of the important methods to develop the new molecular functional materials. In particular, we look upon mutual cohesive interactions of hydrogen bonding and metal coordination as one useful tool to construct the preprogramming superstructures. In this study, five controlled superstructures of a one-dimensional linear chain—a zigzag ribbon, right-handed and left-handed helices, and a two-dimensional honeycomb sheet—-are newly created by using the neutral metal complexes with some 2,2′-biimidazolate mono-anions.

Origin of the enhancement of the second hyperpolarizability of singlet diradical systems with intermediate diradical character

The origin of the diradical character dependence of the second hyperpolarizability (gamma) of neutral singlet diradical systems is clarified based on the perturbation formula of gamma using the simplest diradical molecular model with different diradical characters, i.e., H2 under bond dissociation. The enhancement of gamma in the intermediate diradical character region turns out to originate from the increasing magnitude of the transition moment between the first and second excited states and the decrease of that between the ground and first excited states, respectively, with the increase in diradical character. This feature confirms that open-shell singlet conjugated molecules with intermediate diradical characters constitute a new class of third-order nonlinear optical systems, whose gamma values can be controlled by the diradical character in addition to the conjugation length.

Molecular electron-spin quantum computers and quantum information processing: pulse-based electron magnetic resonance spin technology applied to matter spin-qubits

Pulse-based Electron–Nuclear and ELectron–electron DOuble Resonance (ENDOR/ELDOR) techniques have been applied to molecular spins in order to implement ensemble electron spin-qubit based quantum computers/computing (QC) and quantum information processing (QIP) in the solid state. Pulsed ENDOR-based QC/QIP experiments for super dense coding (SDC) have for the first time been carried out by the use of molecular electron- and nuclear-spin entities such as the stable malonyl radical as matter spin-qubits. The spin-qubit manipulation technology for quantum gate operations in this work is based on the time-proportional-phase-increment (TPPI) technique, enabling us to distinguish between the phases of spin-qubit based entangled states. The TPPI technique, as firstly applied by Mehring et al. (M. Mehring, J. Mende and W. Scherer, Phys. Rev. Lett., 2003, 90, 153001), has illustrated the establishment of quantum entanglement between electron- and nuclear-spin states and mutual interconversion between the electron–nuclear Bell states. The electron-spin 4π-periodicity in phase shows up in the QC/QIP experiments, explicitly and experimentally illustrating the electron-spin spinor nature for the first time. Tripartite QC experiments have been made, showing the occurrence of separable states. Also, the development of novel electron-spin technology to manipulate multi-electron spin-qubits is described. In this work, the pulsed coherent-dual ELDOR for QC/QIP has for the first time been implemented by invoking a novel microwave dual phase-rotation technique. Thus, applications of the coherent-dual ELDOR to molecular electron spin-qubit systems are also discussed, emphasising designing the molecular two electron-qubit systems appropriate for QC/QIP. g- and/or hyperfine A-tensor engineering approaches give us the two- and multi-electron-qubit systems, which have been a materials challenge to implement matter spin-qubit based QC/QIP. The targeted matter spin-qubits can be used to facilitate selective resonant microwave excitations achieved by the pulsed ELDOR technique. In addition to DiVincenzos five criteria, general requisites for scalable electron spin-qubit systems as 1D periodic robust spin structures are described. According to the requisites, double- or triple-stranded helicates embedding open-shell metal cations are proposed instead of organic molecular spin-qubits.

MO theoretical studies of magnetic interactions in clusters of nitronyl nitroxide and related species

Abstract Ab initio and semi-empirical molecular orbital calculations are carried out for clusters of nitroxide radicals. The intermolecular effective exchange integrals calculated are positive (ferromagnetic) in the case of appropriately stacked forms of these species. Implications of the calculated results are discussed in relation to the ferromagnetic intermolecular interactions observed for nitroxide radicals such as para-nitrophenyl nitronyl nitroxide.

Three‐Dimensional Intramolecular Exchange Interaction in a Curved and Nonalternant π‐Conjugated System: Corannulene with Two Phenoxyl Radicals

In recent years, curved p-conjugated molecules such as fullerenes and carbon nanotubes have attracted much attention not only in chemistry but also in materials science. Their intra/intermolecular interactions within/between threedimensional (3D) curved p-electron networks play intrinsically vital roles in their unique properties and functionalities. Among them, intramolecular magnetic interaction between electronic spins on a curved p surface was extensively studied for ionic species of C60 such as C60 2 and C60 3 . Their electronic structures are greatly influenced by not only the dynamic spin polarization of electrons but also the negative charges on the spherical p-conjugated system and the countercation. Thus, we have focused on neutral diradical systems, which are known to be the most useful probes for studying intramolecular magnetic interactions in organic molecules. While many neutral diradical derivatives relevant to planar pconjugated systems have so far been investigated, studies on curved p-conjugated neutral diradicals are limited to a single C60-based system in which [60]fullerene is linked to two nitroxide radicals. However, their intramolecular exchange interaction J through the C60 skeleton was very weak (j Jk 1 B j < 0.1 K) because of the small spin delocalization onto the C60 p network from the nitroxide radicals with spin-localized nature on the NO moieties. Therefore, in order to evaluate an intramolecular exchange interaction in a curved p-conjugated system in a quantitative manner, synthesis and isolation of a stable neutral diradical derivative with extensively spindelocalized nature on its curved p-conjugated system have been the focus of current attention in molecular magnetism and open-shell chemistry. 5] Recently, we studied corannulene-based stable neutral monoradical systems, such as a phenoxyl radical derivative 1 with highly spin-delocalized nature on the intrinsically 3D bowl-shaped and nonalternant p-conjugated network. These

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.

Electronic structure of a stable phenalenyl radical in crystalline state as studied by SQUID measurements, cw-ESR, and 13C CP/MAS NMR spectroscopy

Abstract A neat single crystal of phenalenyl radical was obtained for the first time by introducing the substituent group of tert -butyl X-ray structure analysis of the crystal of 2,5,8-tri- tert -butylphenalenyl( 2 ) showed that the two planar radicals face each other with inversion symmetry and are dimerized in the monoclinic crystal. This is supported by the magnetic susceptibility(χ) measurement of the crystalline solid state of 2 The observed temperature dependence of χT was reproduced by assuming the thermal equilibrium between a singlet ground state and excited triplet state of the dimer (2 J/k B = −2000K) with traces of paramagnetic impurity molecules (0.3mol%). The electronic structure of the radical dimer in the crystalline state has been identified also by single-crystal ESR and 13 C CP/MAS NMR measurements. The origin of the large antiferromagnetic interaction is discussed in terms of both the experimentally determined π-spin density distribution of monomer radicals and π MO calculations.

New models for organic magnetic conductors or organic kondo and dense kondo systems

Abstract Ab initio MO calculations have been carried out for neutral and monocation states of organic donor molecules (TTF, DTPY) with radical groups. The effective exchange integral (Jaσ) between a hole spin and a localized spin has been determined nonempirically. Implications of the calculated results are discussed in relation to possibilities of organic ferromagnetic (or ferrimagnetic) conductors (metals) or organic Kondo and dense Kondo states, which have received current interest from the spin-mediated organic superconductivity and high Tc superconductivity.