Ken Hoshiko

π-Conjugated Nickel Bis(dithiolene) Complex Nanosheet

A π-conjugated nanosheet comprising planar nickel bis(dithiolene) complexes was synthesized by a bottom-up method. A liquid-liquid interfacial reaction using benzenehexathiol in the organic phase and nickel(II) acetate in the aqueous phase produced a semiconducting bulk material with a thickness of several micrometers. Powder X-ray diffraction analysis revealed that the crystalline portion of the bulk material comprised a staggered stack of nanosheets. A single-layer nanosheet was successfully realized using a gas-liquid interfacial reaction. Atomic force microscopy and scanning tunneling microscopy confirmed that the π-conjugated nanosheet was single-layered. Modulation of the oxidation state of the nanosheet was possible using chemical redox reactions.

Redox Control and High Conductivity of Nickel Bis(dithiolene) Complex π‑Nanosheet: A Potential Organic Two-Dimensional Topological Insulator

A bulk material comprising stacked nanosheets of nickel bis(dithiolene) complexes is investigated. The average oxidation number is -3/4 for each complex unit in the as-prepared sample; oxidation or reduction respectively can change this to 0 or -1. Refined electrical conductivity measurement, involving a single microflake sample being subjected to the van der Pauw method under scanning electron microscopy control, reveals a conductivity of 1.6 × 10(2) S cm(-1), which is remarkably high for a coordination polymeric material. Conductivity is also noted to modulate with the change of oxidation state. Theoretical calculation and photoelectron emission spectroscopy reveal the stacked nanosheets to have a metallic nature. This work provides a foothold for the development of the first organic-based two-dimensional topological insulator, which will require the precise control of the oxidation state in the single-layer nickel bisdithiolene complex nanosheet (cf. Liu, F. et al. Nano Lett. 2013, 13, 2842).

A photofunctional bottom-up bis(dipyrrinato)zinc(II) complex nanosheet

Two-dimensional polymeric nanosheets have recently gained much attention, particularly top-down nanosheets such as graphene and metal chalcogenides originating from bulk-layered mother materials. Although molecule-based bottom-up nanosheets manufactured directly from molecular components can exhibit greater structural diversity than top-down nanosheets, the bottom-up nanosheets reported thus far lack useful functionalities. Here we show the design and synthesis of a bottom-up nanosheet featuring a photoactive bis(dipyrrinato)zinc(II) complex motif. A liquid/liquid interfacial synthesis between a three-way dipyrrin ligand and zinc(II) ions results in a multi-layer nanosheet, whereas an air/liquid interfacial reaction produces a single-layer or few-layer nanosheet with domain sizes of >10 μm on one side. The bis(dipyrrinato)zinc(II) metal complex nanosheet is easy to deposit on various substrates using the Langmuir–Schäfer process. The nanosheet deposited on a transparent SnO2 electrode functions as a photoanode in a photoelectric conversion system, and is thus the first photofunctional bottom-up nanosheet.

Crystalline Graphdiyne Nanosheets Produced at a Gas/Liquid or Liquid/Liquid Interface

Synthetic two-dimensional polymers, or bottom-up nanosheets, are ultrathin polymeric frameworks with in-plane periodicity. They can be synthesized in a direct, bottom-up fashion using atomic, ionic, or molecular components. However, few are based on carbon-carbon bond formation, which means that there is a potential new field of investigation into these fundamentally important chemical bonds. Here, we describe the bottom-up synthesis of all-carbon, π-conjugated graphdiyne nanosheets. A liquid/liquid interfacial protocol involves layering a dichloromethane solution of hexaethynylbenzene on an aqueous layer containing a copper catalyst at room temperature. A multilayer graphdiyne (thickness, 24 nm; domain size, >25 μm) emerges through a successive alkyne-alkyne homocoupling reaction at the interface. A gas/liquid interfacial synthesis is more successful. Sprinkling a very small amount of hexaethynylbenzene in a mixture of dichloromethane and toluene onto the surface of the aqueous phase at room temperature generated single-crystalline graphdiyne nanosheets, which feature regular hexagonal domains, a lower degree of oxygenation, and uniform thickness (3.0 nm) and lateral size (1.5 μm).

New aspects in bis and tris(dipyrrinato)metal complexes: bright luminescence, self-assembled nanoarchitectures, and materials applications

Dipyrrins serve as monovalent bidentate ligand molecules that coordinate to various cations. Their BF2 complexes, 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene and its derivatives (BODIPYs), exhibit excellent photostability, strong light absorption, and high fluorescence quantum yield, thereby encouraging their application in various fields, e.g., as biological and biomedical fluorescent markers. Dipyrrin may also accept a wide variety of metal ions spontaneously. However, dipyrrin metal complexes have been disregarded from materials science research. This review article summarizes recent progress in bis(dipyrrinato)metal(II) and tris(dipyrrinato)metal(III) complexes from the viewpoint of materials chemistry. Section 2 describes a series of efforts aimed to realize intense luminescence superior to or comparable with that of BODIPYs. The spontaneous coordination of these complexes enables them to construct self-assembled nanoarchitectures, such as supramolecules and coordination polymers that form one-dimensional nanowires, two-dimensional nanosheets, and metal–organic frameworks. Section 3 describes such alluring molecular superstructures. Section 4 discusses potential applications based on these nanoarchitectures, such as thermoelectric and photoelectric conversion.

Photofunctionality in Porphyrin-Hybridized Bis(dipyrrinato)zinc(II) Complex Micro- and Nanosheets

New bis(dipyrrinato)zinc(II) complex micro- and nanosheets containing zinc(II) porphyrin (N2) are synthesized. A liquid/liquid interface method between dipyrrin porphyrin ligand L2 and zinc acetate produces N2 with a large domain size. N2 can be layered quantitatively onto a flat substrate by a modified Langmuir-Schäfer method. N2 deposited on a SnO2 electrode functions as a photoanode for a photoelectric conversion system. The photoresponse of N2 covers the whole visible wavelength range (400-650 nm), with a maximum quantum efficiency of more than twice that of a bis(dipyrrinato)zinc(II) complex nanosheet without porphyrin.

π-Conjugated Trinuclear Group-9 Metalladithiolenes with a Triphenylene Backbone

Previously, we synthesized π-conjugated trinuclear metalladithiolene complexes based on benzenehexathiol (J. Chem. Soc., Dalton Trans.1998, 2651; Dalton Trans.2009, 1939; Inorg. Chem.2011, 50, 6856). Here we report trinuclear complexes with a triphenylene backbone. A reaction with triphenylenehexathiol and group 9 metal precursors in the presence of triethylamine gives rise to trinuclear complexes 9-11. The planar structure of 11 is determined using single crystal X-ray diffraction analysis. The ligand-to-metal charge transfer bands of 9-11 move to longer wavelengths compared with those of mononuclear 12-14. Electrochemical measurements disclose that the one-electron and two-electron reduced mixed-valent states are stabilized thermodynamically. UV-vis-NIR spectroscopy for the reduced species of 9 identifies intervalence charge transfer bands for 9(-) and 9(2-), substantiating the existence of electronic communication among the three metal nuclei. These observations prove that the triphenylene backbone transmits π-conjugation among the three metalladithiolene units.

A bis(terpyridine)iron network polymer on carbon for a potential energy storage material

A bis(terpyridine)iron network polymer was fabricated by electropolymerisation on a glassy carbon electrode. The modified electrode allowed high-speed charging and discharging with a minor capacity decay (only 5% after 3000 cycles at 1 V s(-1)).