Yoshiro Yamashita

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.

Organic metals based on butterfly-shaped donor molecules

Abstract A novel butterfly-shaped bis(1,3-dithiole) donors containing a fused naphthalene and a 1,2,5-thiadiazole ring afforded cation radical salts showing metallic temperature dependence of conductivity.

Synthesis and characterization of novel strong electron acceptors: bithiazole analogues of tetracyanodiphenoquinodimethane (TCNDQ)

Abstract Novel electron acceptors, bithiazole analogues of tetracyanodiphenoquinodimethane (TCNDQ), were synthesized by using a Pd-catalyzed coupling reaction of a dibromated precursor with sodium dicyanomethanide. The new acceptors show strong electron-accepting ability and small on-site Coulomb repulsion. The X-ray crystallographic analysis has revealed a planar structure containing a double bond with E-configuration. Several charge transfer complexes were obtained with electron donors such as tetrathiafulvalene (TTF).

First stable tetracyanodiphenoquinodimethane with a completely planar geometry: Preparation, X-ray structure, and highly conductive complexes of bis[1,2,5]thiadiazolo-TCNDQ

The titled tetracyanodiphenoquinodimethane (TCNDQ) derivative was newly designed and prepared as a novel component for highly conductive organic materials. Introduction of 1,2,5-thiadiazole rings into the TCNDQ skeleton leads to large stabilization in the neutral state. X-ray analysis has revealed their structural details which suggest that interatomic interactions (CH…N, S…N) play an important role in determining the molecular and crystal structure. The novel electron acceptor shows strong electron affinity comparable with that of TCNQ, and gave highly conductive charge-transfer (CT) complexes and an anion radical salt.

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.

New electron acceptors containing thieno[3,4-b]pyrazine units

Tetracyano-p-quinodimethane (TCNQ) analogues containing the title heterocyclic units were synthesized, and the interesting crystal structures of the neutral compounds and the charge-transfer complexes with TTF were revealed by X-ray analysis.

Synthesis and properties of novel tetrathiafulvalene vinylogues

The cation radical states of novel TTF vinylogues with o-substituted phenyl groups at the vinyl positions are thermodynamically stable, and X-ray analyses of the cation radical salts have revealed the planar structures of the TTF vinylogue parts and unique crystal structures.

Novel organic metals based on nonplanar Bis(1,3-Dithiole) donors

Novel nonplanar bis(1,3-dithiole) donors with small on-site Coulomb repulsion afforded unusual cation radical salts as single crystals whose properties were strikingly affected by the incorporated solvent molecules.

OXIDATIVE INTRAMOLECULAR CYCLIZATION OF 2,2'-BIS-1,4-DITHIAFULVEN-6-YL)-3,3'-BITHIENYLS AFFORDING NOVEL BIS(1,3-DITHIOLE) ELECTRON DONORS

The title bis(1,3-dithiole) compounds containing a 3,3′-bithienyl unit undergo an intramolecular coupling reaction at the 6-positions of the dithiafulvenyl groups by oxidation to give cyclization products in high yields.