Masaaki Tomura

Synthesis and Properties of Benzobis(thiadiazole)s with Nonclassical π-Electron Ring Systems

Abstract Benzo[1,2-c:4,5-c′]bis([1,2,5]thiadiazole) containing a hypervalent sulfur atom has a low LUMO energy. The aryl derivatives were synthesized using a Stille coupling reaction. The selenadiazole analogues were also prepared. The electron accepting properties of these nonclassical heterocycles were shown by their high reduction potentials. Introduction of electron-donating groups into the electron-withdrawing heterocycles afforded novel donor-acceptor compounds. Their cyclic voltammograms showed that they are easily both oxidized and reduced. Some of them have the absorption maxima above 700 nm due to the small HOMO-LUMO separation. X-ray structure analysis of the diphenyl derivative revealed the formation of a tape-like network through short S⋯N contacts.

Highly polarized electron donors, acceptors and donor–acceptor compounds for organic conductors

New types of π-electron donors and acceptors with high polarizability are reviewed. TTF derivatives with polarizable substituents, π-extended TTF analogues fused with nitrogen-containing heterocycles and non-TTF donors (i.e. electron donors) and chalcogen atom-containing quinones, TCNQ and DCNQI analogues (i.e. electron acceptors) are described. Donor–acceptor compounds showing electrochemically amphoteric properties are also discussed.

Synthesis, crystal structure, and electron-accepting property of the BF2 complex of a dihydroxydione with a perfluorotetracene skeleton.

A BF(2) complex containing an octafluorotetracene moiety was synthesized as a new type of electron acceptor. This compound exhibits a long-wavelength absorption based on the perfluorotetracene skeleton and high electron affinity due to its quadrupolar structure enhanced by fluorination. In the crystal, the molecules are arranged with short F...pi and F...F contacts affording a dense crystal packing. The BF(2) complex exhibited n-type semiconducting behavior.

Synthesis and Properties of Terthiophene and Bithiophene Derivatives Functionalized by BF2 Chelation: A New Type of Electron Acceptor Based on Quadrupolar Structures

Terthiophene and bithiophene derivatives functionalized by BF(2) chelation were synthesized as a new type of electron acceptor, and their properties were compared to those of bifuran and biphenyl derivatives. These new compounds are characterized by quadrupolar structures due to resonance contributors generated by BF(2) chelation. The bithiophene derivative has a strong quadrupolar character compared with the bifuran and biphenyl derivatives because their hydrolytic analyses indicated that the bithiophene moiety has a larger on-site Coulomb repulsion than the others. The terthiophene derivative has a smaller on-site Coulomb repulsion than the bithiophene derivative due to the addition of a thiophene spacer. These BF(2) complexes exhibit long-wavelength absorptions and according to measurements of ionization potentials and absorption edges they have energetically low-lying HOMOs and LUMOs. The crystal structure of the bithiophene derivative is of the herringbone type, with short F···S and F···C contacts affording dense crystal packing. n-Type semiconducting behaviour was observed in organic field-effect transistors based on these BF(2) complexes.

A linear chain of water molecules accommodated in a macrocyclic nanotube channel.

A macrocyclic tetramer of 2-phenyl-1,3,4-oxadiazole was synthesized, and its self-assembly was investigated. The macrocycle was stacked to form a one-dimensional (1D) columnar structure containing water molecules. The nanotube self-assembled into a bundle, which grew into a molecular wire. The association of the water molecules in the tubular cavity resulted in shielding of the 1D chain of water molecules by the nanotube; these macrocyclic nanotube channels are promising candidates for nanotechnological applications.

(Dibenzoylmethanato)boron difluoride derivatives containing triphenylamine moieties: a new type of electron-donor/π-acceptor system for dye-sensitized solar cells.

(Dibenzoylmethanato)boron difluoride derivatives containing triphenylamine moieties were synthesized as a new type of electron-donor/π-acceptor system. These new compounds exhibited long-wavelength absorptions in the UV/Vis spectra, and reversible oxidation and reduction waves in cyclic voltammetry experiments. Their amphoteric redox properties are based on their resonance hybrid forms, in which a positive charge is delocalized on the triphenylamine moieties and a negative charge is localized on the boron atoms. Molecular orbital (MO) calculations indicate that their HOMO and LUMO energies vary with the number of phenylene rings connected to the difluoroboron-chelating ring. This is useful for optimizing the HOMO and LUMO levels to an iodine redox (I(-)/I3(-)) potential and a titanium dioxide conduction band, respectively. Dye-sensitized solar cells fabricated by using these compounds as dye sensitizers exhibited solar-to-electric power conversion efficiencies of 2.7-4.4 % under AM 1.5 solar light.

Novel TTF vinylogues affording stable cation radicals

Abstract Novel TTF vinylogues with extended π -conjugation have been synthesized using an oxidative dimerization reaction of 1, 4-dithiafulvenes. The cation radicals of the derivatives with o -substituted phenyl groups are thermodynamically stable where the aryl units are twisted and the TTF vinylogue skeleton is planar. Some compounds afforded cation radical salts upon electrochemical oxidation. X-ray structure analyses revealed unusual crystal structures.

Preparation and properties of bis [1,2,5] thiadiazolotetrathiafulvalene

Bis[1,2,5]thiadiazolotetrathiafulvalene (1) was prepared by desulfurization of the corresponding 1,3-dithiole-2-thione (2) with triphenylphosphine. It showed relatively high oxidation potentials due to the electron-withdrawing thiadiazole ring. The X-ray structural analysis revealed that there exist short intermolecular S---S and S---N contacts in the crystal

Hydroxyphenyl substituted tetrathiafulvalene vinylogues affording stable cation radical salts with unusual crystal structures

Abstract TTF vinylogues containing hydroxyphenyl groups were newly prepared. They are stronger electron donors than BEDT-TTF and afforded their cation radical salts as single crystals upon electrochemical oxidation. X-Ray structure analysis has revealed their unusual crystal structures, where π-overlapping and hydrogen bonding play a crucial role in constructing them.

Synthesis, structure, and physical properties of novel component molecules with fused heterocycles for organic conductor

Abstract Novel unsymmetrical tetrathiafulvalene derivatives with a fused 1,2,5-thiadiazole ring have been synthesized. The room temperature electrical conductivities of their 1:1 radical cation salts were found to lie between 10 −6 and 10 −1 S cm −1 . The X-ray crystallographic analyses of the radical cation salts revealed that there exist short intermolecular S…N and S…S heteroatom contacts in the crystals.