Faculty Profiles - AWAGA, Kunio

Influence of Air Exposure on Photocarrier Generation in Amorphous and Phase II Thin Films of Titanyl Phthalocyanine Reviewed

Eguchi, Keitaro, Imai, Yoshiaki, Matsushita, Michio M., Awaga, Kunio

Journal of Physical Chemistry C Vol. 122 ( 14 ) page： 7731 - 7736 2018.4

Nanopore-induced host-guest charge transfer phenomena in a metal-organic framework Reviewed

S. Yamamoto, J. Pirillo, Y. Hijikata, Z. Zhang, K. Awaga

Chemical Science Vol. 9 ( 13 ) page： 3282 - 3289 2018.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Royal Society of Chemistry

A spontaneous entrapment of electron-donating small guest molecules, including tetrathiafulvalene (TTF) and N,N,N′,N′-tetramethyl-1,3-propanediamine (TMPDA), was realized in a structurally flexible metal-organic framework, {Mn7(2,7-AQDC)6(2,6-AQDC)(DMA)6}∞ (AQDC = anthraquinone dicarboxylates, DMA = N,N-dimethylacetamide), with electron-accepting anthraquinone groups, generating two MOF guest charge transfer complexes: {Mn7(2,7-AQDC)6(2,6-AQDC)(DMA)6(TTF)5} and {Mn7(2,7-AQDC)6(2,6-AQDC)(DMA)4(H2O)2(TMPDA)7}. Using a mild impregnation procedure, single crystals of the target complexes were obtained via a crystal-to-crystal conversion, and the crystals were suitable for structural analysis. Single crystal X-ray analysis demonstrated the different arrangements of these intercalated donor molecules: some donor molecules interacted with the anthraquinone groups and formed infinite D-A-A-D stacks, some appeared beside the anthraquinone groups but only formed donor-acceptor pairs, and the remainder of the molecules simply filled the space. The charge transfer between the guests and the framework was spectroscopically confirmed, and the radical densities on the organic species were estimated using magnetic susceptibility measurements. Compared with a solid-state mixture of anthraquinone and donor molecules, the evenly distributed donor molecules in the micropores of the MOF resulted in a "solid solution" state and significantly promoted the degree of charge transfer between donors and acceptors. Such an encapsulation process may be adopted as a new strategy for post-modification of the electronic and magnetic properties of MOFs, as well as for generating new semiconducting charge-transfer complexes.

DOI： 10.1039/c7sc05390h

Controlling the crystallinity and crystalline orientation of "shuttlecock" naphthalocyanine films for near-infrared optoelectronic applications Reviewed

Simon Dalgleish, Louisa Reissig, Yoshiaki Shuku, Christophe Gourlaouen, Sergi Vela, Kunio Awaga

Journal of Materials Chemistry C Vol. 6 ( 8 ) page： 1959 - 1970 2018.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Royal Society of Chemistry

The thin film properties of tin(ii) 2,3-naphthalocyanine (SnNPc) were interrogated and various strategies for controlling the crystallinity and crystalline orientation within the films were assessed. SnNPc is shown to crystallize in the space group P21/c (Z = 4), where the molecular arrangement consists of alternating layers of concave and convex overlap, induced by the out-of-plane Sn atoms, resulting in a 3D slipped-π-stack network structure analogous to that reported for Phase I of titanyl phthalocyanine. The thin films were studied by X-ray diffraction, atomic force microscopy and absorption spectroscopy and are highly sensitive not just to the conditions during growth, but also to substrate pre- and post-deposition treatment. While the films grown at room temperature were largely amorphous, the crystallinity was enhanced with substrate temperature, with the molecules orienting in a standing molecular geometry. A thin layer of 3,4:9,10-perlenetetracarboxylic dianhydride induces a lying molecular geometry of the same polymorph as that of the single crystal, while different polymorphs are accessible through solvent vapor annealing of amorphous films. Transient photocurrent measurements showed a dramatic improvement in photodetector device bandwidth for the lying molecular geometry, which was attributed to enhanced photoconductivity along the π-stacking axis, while solvent vapor annealing could be used to tune the photosensitivity across the near-infrared region.

DOI： 10.1039/c7tc05521h

Giant negative magnetoresistance in Ni(quinoline-8-selenoate)2 Reviewed

Nicholas Black, Tonouchi Daiki, Michio M. Matsushita, J. Derek Woollins, Kunio Awaga, Neil Robertson

Physical Chemistry Chemical Physics Vol. 20 ( 1 ) page： 514 - 519 2018.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Royal Society of Chemistry

The magnetic, structural, conductivity and magnetoresistance properties of [Ni(quinoline-8-selenoate)2] ([Ni(qs)2]) have been studied. Despite the insolubility of the material necessitating its study as a powdered sample, a remarkably high conductivity has been measured. The conductivity is an order of magnitude greater than the thin-film processable thiol analogue previously reported and has been interpreted through the same space-charge limited conduction mechanism with charges injected from the electrodes. The introduction of selenium, results in a material with conductivity approaching metallic due to the enhanced interaction between adjacent molecules. Additionally, under an applied magnetic field, the material displays a negative magnetoresistance effect above 35% at 2 K. The effect can still be observed at 200 K and is interpreted in terms of a double-exchange mechanism.

DOI： 10.1039/c7cp06273g

Electrochemical Synthesis and Doping for Nano-Porous Organic Magnetic Materials

Shuku Yoshiaki, Awaga Kunio

WORLD SCIENTIFIC REFERENCE ON SPIN IN ORGANICS, VOL 4 - SPIN IN ORGANICS Vol. 10 page： 207 - 234 2018

A Novel Strategy to Functionalize Covalent Organic Frameworks for High-Energy Rechargeable Lithium Organic Batteries via Graft Polymerization in Nano-Channels Reviewed

Yang Wu, Zhongyue Zhang, Shunji Bandow, Kunio Awaga

BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN Vol. 90 ( 12 ) page： 1382 - 1387 2017.12

Language：English Publishing type：Research paper (scientific journal) Publisher：CHEMICAL SOC JAPAN

By introducing catalyst- and solvent-free graft polymerization of low cost and environmentally benign sulfur to the nano-channels of an imine-linked covalent organic framework (COF), we demonstrated our strategy for functionalization of a conventional COF to yield a redox-active covalent organic framework-graft-polysulfide (COF-graft-PS), which can be utilized as a cathode active material in rechargeable lithium organic batteries. The COF-graft-PS-based batteries showed high capacity (425 mA h g(-1) at a rate of 250 mA g(-1)), excellent rate capability, and good cycling performance over 500 cycles. The design characteristics and synthetic strategy open new possibilities for the preparation of alternative, sustainable, high-performance rechargeable lithium batteries by using abundant and cost-effective materials.

DOI： 10.1246/bcsj.20170247

3D Spin-Liquid State in an Organic Hyperkagome Lattice of Mott Dimers Reviewed

Asato Mizuno, Yoshiaki Shuku, Michio M. Matsushita, Masahisa Tsuchiizu, Yuuki Hara, Nobuo Wada, Yasuhiro Shimizu, Kunio Awaga

PHYSICAL REVIEW LETTERS Vol. 119 ( 5 ) page： 057201 2017.7

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER PHYSICAL SOC

We report the first 3D spin liquid state of isotropic organic spins. Structural analysis, and magnetic and heat-capacity measurements were carried out for a chiral organic radical salt, (TBA)(1.5) [(-)-NDI-Delta] (TBA denotes tetrabutylammonium and NDI denotes naphthalene diimide), in which (-)-NDI-Delta forms a K-4 structure due to its triangular molecular structure and an intermolecular pi-pi overlap between the NDI moieties. This lattice was identical to the hyperkagome lattice of S = 1/2 Mott dimers, and should exhibit 3D spin frustration. In fact, even though the high-temperature magnetic susceptibility followed the Curie-Weiss law with a negative Weiss constant of theta = -15 K, the low-temperature magnetic measurements revealed no long-range magnetic ordering down to 70 mK, and suggested the presence of a spin liquid state with a large residual paramagnetism chi(0) of 8.5 x 10(-6) emu g(-1) at the absolute zero temperature. This was supported by the N-14 NMR measurements down to 0.38 K. Further, the low-temperature heat capacities c(p) down to 68 mK clearly indicated the presence of c(p) for the spin liquid state, which can be fitted to the power law of T-0.62 in the wide temperature range 0.07-4.5 K.

DOI： 10.1103/PhysRevLett.119.057201

Negative differential resistance in the Peierls insulating phases of TTF-TCNQ Reviewed

Daiki Tonouchi, Michio M. Matsushita, Kunio Awaga

PHYSICAL REVIEW B Vol. 96 ( 4 ) page： 045116 2017.7

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER PHYSICAL SOC

Negative differential resistance (NDR) was observed in the most well known organic conductor, TTF-TCNQ, in its low-temperature Peierls insulator phase below 53 K. The voltage-current (V -I) characteristics below this temperature, measured by a four-probe method, exhibited unique NDR behavior, in which the dV/dI versus conductivity (sigma) plots had the inflection points at the three sigma values without depending on temperature. These sigma values were found to coincide with the conductivities at the three transition temperatures (53, 49, and 38 K) for the formation of the charge-density waves in TTF-TCNQ. This suggests that the electronic structure of the Peierls insulating phase of TTF-TCNQ is governed by the total carrier density, which is determined by not only thermal excitation but also carrier injection.

DOI： 10.1103/PhysRevB.96.045116

Templating effects of tetrakis(thiadiazole) porphyrazine on the structure and optical properties of copper phthalocyanine thin films Reviewed

Eguchi, Keitaro, Heutz, Sandrine, Awaga, Kunio

Journal of Porphyrins and Phthalocyanines Vol. 21 ( 4-6 ) page： 322 - 326 2017.4

Molecular and thin film properties of cobalt half-sandwich compounds for optoelectronic application Reviewed

Maxwell Reinhardt, Simon Dalgleish, Yoshiaki Shuku, Louisa Reissig, Michio M. Matsushita, Jason Crain, Kunio Awaga, Neil Robertson

PHYSICAL CHEMISTRY CHEMICAL PHYSICS Vol. 19 ( 9 ) page： 6768 - 6776 2017.3

Language：English Publishing type：Research paper (scientific journal) Publisher：ROYAL SOC CHEMISTRY

The structure and electronic properties of a novel cobalt half sandwich complex of cyclopentadiene (Cp) and diaminonaphthalene (DAnap) [CpCo(DAnap)] are described and compared to the previously reported diaminobenzene derivative [CpCo(DAbnz)] in view of their potential for (opto) electronic device application. Both complexes show stable redox processes, tunable through the diaminoacene ligand, and show strong absorption in the visible region, with additional transitions stretching into the near infrared (NIR). CpCo(DAnap) crystallises with a particularly large unit cell (9301 angstrom 3), comprising 32 molecules, with a gradual rotation over 8 molecules along the long c-axis. In the solid state the balance of the optical transitions in both complexes is reversed, with a suppression of the visible band and an enhancement of the NIR band, attributed to extensive intermolecular electronic interaction. In the case of CpCo(DAnap), highly crystalline thin films could be formed under physical vapor deposition, which show a photocurrent response stretching into the NIR, and p-type semiconductor behavior in field effect transistors with mobility values of the order 1 x 10-(4) cm(2) V-1 s(-1). The device performance is understood through investigation of the morphology of the grown films.

DOI： 10.1039/c6cp08685c