Two methylated bis(ethylenedithio)tetrathiafulvalene (ET) derivatives, Me2ET and Me4ET were stereoselectively synthesized to examine the effect of methylation on conformations of dihydrodithiin rings and molecular arrangements in the crystalline state. Since the donating ability of Me2ET and Me4ET are similar to that of ET, the methylated ET derivatives are considered to be appropriate to investigate the “lattice pressure” effect on ET radical salts by changing the volume of donor molecules. The upper limit of an activation energy for the ring inversion of the dimethylated dihydrodithiin in solution was estimated to be 32 kJ mol−1 by 13C NMR spectroscopy. The X-ray structure analyses revealed that orientations of methyl groups are fixed to axial in Me2ET and to equatorial in Me4ET, accompanied by the change of molecular stacking. The “volume of a methyl group” was evaluated by comparing the molecular volumes of Me2ET and Me4ET with that of ET, and the effective volume for the axial methyl group turns out to be 15% larger than that of the equatorial. The solid state 13C NMR (CP/MAS) spectra of ET and its derivatives showed that the chemical shifts of resonance lines reflect the conformations of dihydrodithiin rings in crystals.

The X-ray crystallographic analysis of 8-fluoro-1-(p-anisylselanyl)naphthalene (1) revealed that the F and Se atoms and the ipso-carbon of the p-anisyl group (C(An)) aligned linearly. The F atom and the Se-C(An) bond lay on the naphthyl plane: the nonbonded distance between F and Se atoms was 2.753(3) Å and the FSeC(An) angle was 175.0(1)°. Ab initio MO calculations with the 6-311++G(3df,2pd) basis sets performed on the model compound of 1, HF‚‚‚SeH 2 , where the aryl groups of 1 were replaced by hydrogens. The calculations exhibited that the energy minimum was achieved when the F, Se, and C(An) atoms aligned linearly. Charge transfer in the formation of HF‚‚‚SeH 2 was suggested to occur from F to SeH 2 on the basis of natural population analysis, which supported the np x (F)-σ*(Se-C(An)) interaction.

Network structures made of p-conjugated molecular wires of oligothiophene 3mer, or 9mer carrying thiol groups at a,v-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 p-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 (y0.1 meV) at temperatures lower than 30 K and non-linear current-voltage characteristics (I 3 V 3 ) appeared in p-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.

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