Tetsuro Kusamoto

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).

Luminescence, Stability, and Proton Response of an Open‐Shell (3,5‐Dichloro‐4‐pyridyl)bis(2,4,6‐trichlorophenyl)methyl Radical

A luminescent open-shell organic radical with high chemical stability was synthesized. (3,5-Dichloro-4-pyridyl)bis(2,4,6-trichlorophenyl)methyl radical (PyBTM) was photoluminescent under various conditions. Fluorescence quantum yields of 0.03, 0.26, and 0.81 (the highest value reported for a stable organic radical) were obtained in chloroform, in poly(methyl methacrylate) film at room temperature, and in an EPA matrix (diethyl ether:isopentane:ethanol) at 77 K, respectively. The photostability of PyBTM is up to 115 times higher than that of the tris(2,4,6-trichlorophenyl)methyl radical, a previously reported luminescent radical. The pyridine moiety of PyBTM acts as a proton coordination site, thereby allowing for control of the electronic and optical properties of the radical by protonation and deprotonation.

Realization of SOMO−HOMO Level Conversion for a TEMPO-Dithiolate Ligand by Coordination to Platinum(II)

We developed a TEMPO-bound dithiolate ligand (= tempodt) and its Pt(diimine)(dithiolate) complex to realize a unique electronic structure with the potential for unprecedented functionalities. The physical properties and electronic structures of tempodt, (tempodt)Pt, and their related compounds were investigated by cyclic voltammetry, UV-visible spectroscopy, electron spin resonance (ESR) spectroscopy, and other techniques. It was revealed that (tempodt)Pt showed an unusual electronic structure in which the HOMO level (= pi-conjugated dithiolate-based orbital) was located above the SOMO level attributed to the TEMPO moiety, and that this situation was achieved via a drastic electronic structure change of SOMO-HOMO level conversion through complex formation. These findings were further supported by an investigation into a one-electron oxidized (tempodt)Pt and related complexes.

Double protonation of 1,5-bis(triarylaminoethynyl)anthraquinone to form a paramagnetic pentacyclic dipyrylium salt.

Protonation-induced intramolecular cyclization reactions of new donor (D)-acceptor (A) and D-A-D conjugated molecules 1-triarylaminoethynylanthraquinone (1-AmAq) and 1,5-bis(triarylaminoethynyl)anthraquinone (1,5-Am(2)Aq), respectively, were achieved. The former undergoes monoprotonation with bis(trifluoromethanesulfone)imide acid (TFSIH) to give pyrylium salt [1-AmPyl]TFSI, whereas the latter undergoes a novel double proton cyclization reaction to yield 1,5-bis(triarylamino)dipyrylium salt [1,5-Am(2)Pyl(2)](TFSI)(2) with a new pentacyclic backbone. This divalent cationic salt can be reduced to give the neutral species 2,8-bis(triarylamino)benzo[de]isochromeno[1,8-gh]chromene ([1,5-Am(2)Pyl(2)](0)), which maintains the planar pentacyclic backbone. The obtained condensed-ring compounds show unique optical, electrochemical, and magnetic properties due to the extremely narrow HOMO-LUMO gap. In particular, the dication [1,5-Am(2)Pyl(2)](2+) shows paramagnetic behavior with two spins centered on two triarylamine moieties through valence tautomerization with the pentacyclic backbone.

Photoelectric signal conversion by combination of electron-transfer chain catalytic isomerization and photoisomerization on benzodimethyldihydropyrenes.

Photochromic benzocyclophanediene showed oxidation-triggered isomerization to form benzodimethyldihydropyrene. The isomerization proceeded via an autocatalytic reaction system, which could be combined with the photochromic nature of the molecule to establish a new photoelectric signal conversion system.

Enhanced Luminescent Properties of an Open-Shell (3,5-Dichloro-4-pyridyl)bis(2,4,6-trichlorophenyl)methyl Radical by Coordination to Gold†

A gold(I) complex containing an open-shell luminescent (3,5-dichloro-4-pyridyl)bis(2,4,6-trichlorophenyl)methyl (PyBTM) radical was prepared. The complex showed fluorescence centered mainly on the coordinated PyBTM ligand. The photophysical and photochemical properties were positively modulated upon coordination to Au(I); the photoluminescence quantum yield, fluorescence wavelength, and the stability in the photoexcited state all increased.

Cyclization of TEMPO Radicals Bound to Metalladithiolene Induced by SOMO–HOMO Energy-Level Conversion†

In recent decades, it has been demonstrated that the appropriate control of the electronic structure of a metalladithiolene moiety in several planar metalladithiolenes is a promising way to realize desired physical and/or chemical properties. We have recently developed a new metalladithiolene containing a 2,2,6,6-tetramethyl-1-piperidinyl Noxide (TEMPO) radical moiety, (tempodt)Pt, and have revealed that this complex has a quite unique electronic structure, in which the energy level of the singly occupied molecular orbital (SOMO; resulting from the TEMPO radical) is lower than that of the highest occupied molecular orbital (HOMO; centered on the p-conjugated dithiolene moiety). One-electron (1e ) oxidation of the complex led to the generation of a p radical on the HOMO. Next, we focused on the application of this unique electronic structure to the development of new chemical phenomena, by employing planar metalladithiolenes, [M(dithiolene)2] n (M = Au, Ni; n = 0, 1, 2). These complexes are well known to have interesting electronic structures in which their HOMOs (SOMOs) delocalize over p-conjugated dithiolene ligands, and they are easily oxidized to produce ligand-based p-radical species. From this perspective, we designed novel planar metalladithiolenes [M(tempodt)2] n 1 (1a : M = Au, n = 1; 1b : M = Ni, n = 2). These compounds are composed of a planar p-conjugated dithiolene moiety and two TEMPO radical moieties. Because of a strong donating ability of this type of p-conjugated dithiolene skeleton, a SOMO–HOMO converted electronic structure similar to (tempodt)Pt was expected for compound 1. It was also expected that a p radical would be produced on the p-conjugated skeleton upon 1e oxidation, and that the resulting multispin species would show peculiar chemical reactivity and/or physical properties. Herein, a particular intramolecular cyclization by radical coupling through 1 according to this scenario is reported. The complexes 1 a, 2a, and 2b were newly synthesized by reaction of tempodtR2 with NaAuCl4 or NiCl2 in the presence of Bu4NOH in THF/MeOH (see the Supporting Information). In the case of M = Au, 1a and the reduced side products were initially formed as purple precipitates, followed by precipitation of the green solid 2 a, whereas compound 2b formed as a dark green precipitate when M = Ni. Note that a [Ni(dithiolene)2] 2 dianion species generated in situ is spontaneously oxidized to afford the [Ni(dithiolene)2] ion. This difference in behavior was attributed to differences in donating ability: the Ni-containing p-conjugated skeleton was much more easily oxidized than the Au-containing one (Supporting Information, Figure S1). The molecular structure of 1a, analyzed by single-crystal XRD, is shown in Figure 1a. The Au atom was located at the

Towards molecular batteries: coverage of small aminosilica nanoparticles with ferrocenyl and pentamethylferrocenyl groups and their redox properties

Small aminosilica nanoparticles (NPs, 12 nm SiO2 core) were covered with ferrocenyl (Fc) and pentamethylferrocenyl (Fc*) groups by reactions with metallocenyl carbonyl chlorides. Cyclic voltammetry in methanol/acetonitrile showed a single fully chemically- and electrochemically-reversible wave with a diffusion-controlled current; colorimetric titrations with [FcCOMe][BF4] of the Fc-SiO2 and Fc*-SiO2 NPs indicated a coverage of the aminosilica NPs of 335 ± 50 Fc or 240 ± 40 Fc* groups.

Highly photostable luminescent open-shell (3,5-dihalo-4-pyridyl)bis(2,4,6-trichlorophenyl)methyl radicals: significant effects of halogen atoms on their photophysical and photochemical properties

Novel luminescent radicals, Br2PyBTM and F2PyBTM were synthesized and their structures, spectroscopic properties, photostability, and electronic structures were compared with those of Cl2PyBTM. Br2PyBTM showed the highest photostability and F2PyBTM displayed the highest photoluminescence quantum yield of the three radicals.

Bilayer Mott system based on Ni(dmit)2 (dmit = 1,3-dithiole-2-thione-4,5-dithiolate) anion radicals: two isostructural salts exhibit contrasting magnetic behavior.

A new class of Ni(dmit)(2) anion radical salt (Et-2,5-DBrP)[Ni(dmit)(2)](2) (1) (Et-2,5-DBrP = ethyl-2,5-dibromopyridinium) was developed. Single-crystal X-ray diffraction analysis indicates that this salt contains two crystallographically independent anion layers in the crystal with effective Br···S halogen bonds between the cation and the anion. The crystal and electronic structures, and electrical and magnetic measurements reveal that 1 is a novel bilayer Mott system, in which two different Mott-insulating anion layers coexist in one crystal. Selective halogen substitution of Br with I at the 2-position in the cation affords the isostructural bilayer salt (Et-2I-5BrP)[Ni(dmit)(2)](2) (2) (Et-2I-5BrP = ethyl-2-iodo-5-bromopyridinium), while substitution at the 5-position results in a structural change, yielding the monolayer salt (Et-2Br-5IP)[Ni(dmit)(2)](2) (3) (Et-2Br-5IP = ethyl-2-bromo-5-iodopyridinium). These results indicate that the halogen bond plays an important role to realize the bilayer system, and that the crystal structure is controlled by tuning the strength of the halogen bond. The low temperature magnetic properties of the two isostructural salts 1 and 2 are significantly different, because they are affected by fluctuated spins that do not participate in the formation of short-range antiferromagnetic domains. The bilayer salt generates the fluctuated spins more easily than conventional monolayer salts, and such fluctuated spins are expected to result in unique physical properties.