Yumi Yakiyama

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.

Selective Formation of Conductive Network by Radical-Induced Oxidation

Cd-based coordination networks having channels were formed selectively by using a redox-active aromatic ligand 2,5,8-tri(4-pyridyl)1,3-diazaphenalene (TPDAP, H(+)1(-)). An electron-conductive network having a π-π stacking columnar structure of TPDAP formed in the presence of a trace amount of TPDAP radical (1(•)). In contrast, a nonconductive network having a dimer unit of H(+)1(-) formed in the absence of 1(•). These results suggest the presence of a unique oxidation mechanism of TPDAP induced by formation of H(+)1(-)-1(•) dimer, which was initiated by a trace amount of 1(•). The dimerization increased HOMO level of H(+)1(-) moiety within the dimer to generate further radicals that could not form when H(+)1(-) was well isolated in CH3OH.

Proton-transfer salts between an EDT-TTF derivative having imidazole-ring and anilic acids: multi-dimensional networks by acid–base hydrogen-bonds, π-stacks and chalcogen atom interactions

An imidazole-functionalized EDT-TTF derivative afforded the protonated cation species in salts with chloranilate and cyananilate. Multi-dimensional networks were formed by acid–base hydrogen-bonds in the imidazolium moiety, and by π-stacks and chalcogen atom interactions in the EDT-TTF moiety.

Tris(2-hydroxyphenyl)triazasumanene: bowl-shaped excited-state intramolecular proton transfer (ESIPT) fluorophore coupled with aggregation-induced enhanced emission (AIEE)

Tris(2-hydroxyphenyl)triazasumanene ((A)-(+)-1), a bowl-shaped molecule, which possesses 2-(2′-hydroxyphenyl)pyridine moieties, was successfully synthesised. (A)-(+)-1 showed a single peak emission in CH2Cl2, which overlapped with the emission of the triazasumanene skeleton and diminished at a high concentration, corresponding to the formation of the excited enol form. In contrast, single crystals of (A)-(+)-1 exhibited a dual emission with a large Stokes shift, indicating the presence of the excited keto form by the excited state intramolecular proton transfer (ESIPT) process. In the solution of (A)-(+)-1 containing a mixture of a large amount of a poor solvent (hexane or MeOH) and a small amount of CH2Cl2, colloidal aggregates emerged with the continuous increment of emission intensity by further addition of the poor solvent, demonstrating aggregation-induced enhanced emission (AIEE). The analysis of the morphology and the structure of the aggregates using a scanning electron microscope (SEM) and powder X-ray diffraction (PXRD) revealed the well-ordered structure of the aggregates, which possessed a molecular packing pattern similar to that of an (A)-(+)-1 single crystal.

Zwitterionic π-radical involving EDT-TTF-imidazole and F4TCNQ: redox properties and self-assembled structure by hydrogen-bonds and multiple S⋯S interactions

The reaction between an imidazole-functionalized EDT-TTF and F(4)TCNQ produced a zwitterionic pi-radical, which formed a self-assembled structure by the cooperation of hydrogen-bonds and multiple S...S interactions and exhibited three-step oxidation processes and a high electrical conductivity as a single-component organic molecule.

The diversity of Zn(II) coordination networks composed of multi-interactive ligand TPHAP−via weak intermolecular interaction

Kinetic state networks can be trapped by multi-interactive ligands via weak intermolecular interactions. Self-assembly of a tripyridyl multi-interactive ligand K+TPHAP− (potassium 2,5,8-tri(4′-pyridyl)-1,3,4,6,7,9-hexaazaphenalene) and ZnI2 produced seven types of networks depending on the solvent systems (MeOH/additive solvent): [ZnI(TPHAP)]·3.5CH3OH (1) (from MeOH/DMA), [ZnCl0.5I0.5(TPHAP)H2O]·7H2O (2) (from MeOH/DMA + water), [ZnI(TPHAP)]·3PhOH·2CH3OH (3) (from MeOH/phenol ( 50%)), [ZnI(TPHAP)]·2PhNO2·6CH3OH (from MeOH/nitrobenzene) (5), [ZnI(TPHAP)CH3OH]·3PhNH2 (6) (from MeOH/aniline), and [(ZnI)2(TPHAP)(HCON(CH3)2)3(CH3OH)2]+[(ZnI2)2(TPHAP)(HCON(CH3)2)]− (HCON(CH3)2)·4CH3OH (7) (from MeOH/DMF). All structures were characterized by single crystal X-ray structure determination. Each topology was analyzed by TOPOS. The structures were categorized into two- or three-periodic structure. The structural features of each network were explained by the weak intermolecular interactions between TPHAP− and guest molecules. We demonstrated the multi-interactivity of TPHAP− which can recognize slight differences of the weak intermolecular interactions.

Structural Investigation of Chemiresistive Sensing Mechanism in Redox-Active Porous Coordination Network

By changing the rate of evaporation, two kinds of crystalline films composed of redox-active porous coordination networks (1 and 2) were selectively prepared on a gold-patterned substrate using a DMF solution of 2,5,8-tri(4-pyridyl)1,3-diazaphenalene and Cd(NO3)2. We found the highly sensitive humidity sensing ability of film 1. Single crystal structures and infrared spectroscopic analyses before and after hydration of a single crystal of 1 revealed the sensing mechanism: exchange of nitrate ions with water on Cd atoms occurred in hydrated conditions to generate a conductive cationic network.

The Impact of the Polymer Chain Length on the Catalytic Activity of Poly( N -vinyl-2-pyrrolidone)-supported Gold Nanoclusters

Poly(N-vinyl-2-pyrrolidone) (PVP) of varying molecular weight (Mw = 40-360 kDa) were employed to stabilize gold nanoclusters of varying size. The resulting Au:PVP clusters were subsequently used as catalysts for a kinetic study on the sized-dependent aerobic oxidation of 1-indanol, which was monitored by time-resolved in situ infrared spectroscopy. The obtained results suggest that the catalytic behaviour is intimately correlated to the size of the clusters, which in turn depends on the molecular weight of the PVPs. The highest catalytic activity was observed for clusters with a core size of ~7 nm, and the size of the cluster should increase with the molecular weight of the polymer in order to maintain optimal catalytic activity. Studies on the electronic and colloid structure of these clusters revealed that the negative charge density on the cluster surface also strongly depends on the molecular weight of the stabilizing polymers.

Universality of the giant Seebeck effect in organic small molecules

To explore the universality of the giant Seebeck coefficient (>100 mV K−1) found in our previous study with pure C60 thin films, the thermoelectric properties of high-mobility small-molecule organic semiconductors and their temperature dependencies are investigated. Consequently, various pure organic semiconductors exhibited similar large Seebeck coefficients within the temperature range of 300–360 K. The magnitude of the Seebeck coefficient, its intense temperature dependence, and correlation with the activation energy of electrical conductivity are unique and cannot be elucidated by currently known physical models of thermoelectricity.

Crystal Engineering of Coordination Networks Using Multi-interactive Ligands

During molecular assembly processes, weak intermolecular interactions have important functions by precise molecular recognition and stabilization of key metastable intermediates in various kinds of reactions. Introducing these features of weak intermolecular interactions into the confined spaces of porous materials enables selective molecular trapping of metastable species and control of chemical reactions. However, such interactive sites often react with each other or with metal ions during the self-assembly process, thereby resulting in non-interactive stable forms. In this chapter, we describe the potential of using multi-interactive molecules to prepare coordination polymers that possess interactive pores. The multi-interactive π-planar organic ligand, tri(4-pyridyl)hexaazaphenalene, enables the formation of interactive pores by dynamic and selective networking which can be readily controlled by adjusting the reaction conditions. As a result, various porous coordination networks can be prepared from the same starting materials. Furthermore, it enables the formation of kinetic network which can be transformed to thermally more stable one by addition of outer stimuli.