Yuzo Kawada

Design and preparation of pyrrole-based spin-polarized donorsElectronic supplementary information (ESI) available: cyclic voltammograms for N-PN, β-PN, N-TPN, PhNN and TPP. See http://www.rsc.org/suppdata/jm/b2/b211986b/

As a fundamental building block of a conductive magnetic macromolecule, a series of pyrrole derivatives carrying a nitronyl nitroxide (NN) group was prepared. Some of these derivatives afforded ground-state triplet diradical cations upon one-electron oxidation, and the difference in the spin multiplicities of the singly oxidized pyrrolylNNs was rationalized on the basis of a perturbational molecular orbital method. The electronic interaction between the pyrrole and the nitronyl nitroxide parts was also confirmed by cyclic voltammetry and UV-Vis absorption spectroscopy. In spite of the vacancy of the 2 and 5 positions of the pyrrole ring, electrochemical polymerization of these derivatives was not observed, except for an extended α-thienyl derivative.

Preparation of isolable ion-radical salt derived from TTF-based spin-polarized donor

Abstract Galvanostatic electrocrystallization of a TTF-based donor-radical (ETBN) has afforded an ion-radical salt. The radical site of ETBN is intact in the prepared salt and showed paramagnetic behavior. The salt is a semiconductor with conductivity of 10 −2 S/cm at room temperature. Conductivity and magnetic properties are explained as a new type of an ion-radical salt derived from a π-conjugated donor-radical.

Electron transport in networks of gold nanoparticles connected by oligothiophene molecular wires

Network structures made of π-conjugated molecular wires of oligothiophene 3mer, or 9mer carrying thiol groups at α,ω-positions, and gold nanoparticles with average diameter of 4 nm were prepared on interdigitated gold electrodes. Observation of the resultant assemblies by means of FE-SEM and TEM revealed that the gold nanoparticles were connected by π-molecular wires to form a network. The networks exhibited thermally activated electron transport at room temperature with activation energies of 21and 45 meV for 3mer- and 9mer-networks, respectively, and these values were almost the same as those of networks connected with non-conjugated molecules having similar lengths. However, the activation energy became very small (∼0.1 meV) at temperatures lower than 30 K and non-linear current–voltage characteristics (I ∝ V3) appeared in π-conjugated networks at 4.2 K. These results suggest that the gold nanoparticles in the networks work as Coulomb islands and the temperature-independent behavior at lower temperatures can be interpreted in terms of a co-tunneling mechanism.

Phase isomerism in gear-shaped molecules

Abstract The concept of new stereoisomerism due to different phase relations between the labeled cogs in a smoothly geared molecule is described.

Preparation of and dynamic gearing in cis-1,2-bis(9-triptycyl)ethylene

The two tortional degrees of freedom about the bond from the bridgehead to the olefinic carbons in cis-1,2-bis(9-triptycyl)ethylene couple slightly less strongly than those in the corresponding methane in spite of the apparently deeper meshing of the two triptycyl moiety, which manifests itself in the unusually large nuclear spin-spin coupling between the olefinic protons.

Correlation of the two torsional degrees of freedom about the bonds connecting the bridgehead carbons to the sulfur atom in bis (9-triptycyl) sulfide

Abstract Bis(9-triptycyl) sulfides were prepared by pyrolytic extrusion of sulfur dioxide from the corresponding thiosulfonates. A pair of torsional motions about the CS bonds in these sulfides are in strict gearing and require a barrier of 29.3 ± 0.3 kcal/mol for gear slippage.

New synthesis of 2-[1,3-dithiol-2-ylidene]-5,6-dihydro-1,3-dithiolo[4,5-b][1,4]dithiins with formyl group on fused benzene, [1,4]dithiin, or thiophene ring

Abstract As novel TTF-based annelated donors, 2-[1,3-dithiol-2-ylidene]-5,6-dihydro-1,3-dithiolo[4,5- b ][1,4]dithiins with a formyl group on fused benzene, [1,4]-dithiin, or thiophene ring, respectively, were prepared using Diels-Alder or an intramolecular aldol reaction.

Synthesis of 9,10-bis(9-triptycyloxy)triptycenes: molecular design of a system with doubly correlated internal rotation

Abstract Torsional motions around the two C—C and C—O bonds in di(9-triptycyl)methanes, Tp2CH2, and di(9-triptycyl) ethers, Tp2O, respectively, have a high barrier to uncorrelated rotation and a very low barrier to coupled disrotation. As a result, new stereoisomerism is generated due to different phase relationships between appropriately labeled benzene rings, at least one on each Tp unit. To extend the concept and further demonstrate the high correlation in the torsional motions for these systems, a doubly geared molecule, 9,10-bis(3-chlorotriptycyloxy)triptycene (1), was conceived and constructed. Bis(3-chloro-9-triptycyl) 9,10-triptycenebis(peroxycarboxylate) was prepared. The meso and dl isomers of 1 were separated by HPLC on microsilica. The structures were confirmed by high resolution 13C-NMR spectra which revealed an interesting stercochemical feature : one benzene ring of the middle unsubstituted triptycene moiety is diastereotopic to the other two. The rates of isomerization were measured in diphenylmethane solution to give the activation parameters for the gear slipping process: ΔH‡ = 42.1±1.3 kcal mol-1 and ΔS‡ = -3.2±2.3 e.u. The significance of these findings as an extreme case for the dynamics of molecular chains is discussed.

A novel route from triptycenes to a dibenzo(Hafner's hydrocarbon), benz[a]indeno[1,2,3-cd]azulene

Abstract Triptycenes carrying a leaving group at one of the bridgehead carbons afforded the title compound in good to moderate yields when irradiated with a low-pressure Hg lamp. The tropylium ion and the strong CT-complexes of the hydrocarbon were prepared.

Structure And Property Of Cross-Cyclophane Twin Donors

Abstract Cross-cyclophane twin donors, in which long axes of TTF units are fixed in a cross orientation by four ethylenedithio (x-CPTD (II)) and four trimethylenedithio (x-CPTD (III)) chains, were designed and prepared. Although the donor ability of x-CPTD (II) was low due to a heavy bending of the donor units, that of x-CPTD (III) was the same as BEDT-TTF. The crystal structures of a charge transfer complex, x-CPTD (III) ·TCNQ, and an ion radical salt, x-CPTD (III)·Br (1,1,2-TCE)2, revealed that x-CPTD (III) has an ability to construct characteristic self-assembled structures, recognizing a size and a shape of acceptors or counter ions. The almost isotropic conducting property (σr,t //a = 1.0 × 10−2 S · cm−1, σr,t //a = 5.5 × 10−3 S · cm−1) of the ion radical salt was interpreted based on the unique molecular structure of x-CFTD (III).