Self-assembled molecular nanowires of 6,13-Bis(methylthio)pentacene: growth, electrical properties, and applications

We demonstrate a comprehensive study of self-assembled molecular nanowire, including molecular design, one-dimensional crystal growth, resistivity measurement of individual wire, and application to a field-effect transistor. Appropriate molecular design and control of interfacial interactions lead to single crystalline wire growth with an extensive pi-stacking motif. Resistivity measurements of an individual molecular wire indicate that these structural features are advantageous for electrical transport. Finally, field-effect transistors with single- and double-wire channels were fabricated to give some indication of the potential application of the molecular wires.

Exploring electronically polarized pentacenes

Unsymmetrically functionalized pentacenes with electron-rich and/or -poor substituents at the 6- and 13-positions were synthesized. The electronic influence was evaluated by solution-state UV-vis absorption and emission spectroscopies. These materials exhibit good solubility in common organic solvents and are stable in the presence of air and water.

Systematic studies on structural parameters for nanotubular assembly of hexa-peri-hexabenzocoronenes

Thirteen different hexa-peri-hexabenzocoronenes (HBCs) I-III were newly synthesized, and their self-assembling behaviors were investigated. Taking into account also the reported behaviors of amphiphilic HBCs, some structural parameters of HBC essential for the tubular assembly were revealed. Points to highlight include (1) the importance of two phenyl groups attached to one side of the HBC unit, (2) essential roles of long paraffinic side chains on the other side of the phenyl groups, and (3) no necessity of hydrophilic oligo(ethylene glycol) side chains. The hierarchical nanotubular structure, rendered by virtue of a synchrotron radiation technique, was virtually identical to our previous proposal, where the nanotubes are composed of helically coiled bilayer tapes with a tilting angle of approximately 45 degrees. Each tape consists of pi-stacked HBC units, where the inner and outer HBC layers are connected by interdigitation of paraffinic side chains. The coiled structure is most likely caused by a steric congestion of the phenyl groups attached to the HBC unit, whose tilting direction may determine the handedness of the helically chiral nanotube.

Crystal engineering for pi-pi stacking via interaction between electron-rich and electron-deficient heteroaromatics

New dipolar compounds containing alternating electron-rich thieno[3,2-b]thiophene units and electron deficient units have been synthesized. Compounds with 5-pyrimidinyl (compound 2) or benzothiazole (compound 5) as the electron-deficient unit were structurally characterized by the single-crystal X-ray diffraction method. The arrangement of the molecules is found to be one-dimensional slipped-pi-stack for 2. That of 5 is of slipped-pi-stack, albeit with a tilt angle between neighboring pi-stacks. The pi-pi interfacial distances of the molecules in the crystal lattice are 3.47 and 3.59 A for 2 and 5, respectively. On the basis of the crystal structure, compound 2, with negligible pi-pi slip along the short axis of the molecules, has a calculated electronic coupling value (0.153 eV) twice as large as that of the largest coupling of pentacene. Accordingly, the theoretically estimated hole mobility (mu(+)) for 2 (2.32 cm(2) s(-1) V(-1)) compares favorably with that of pentacene (1.93-5.43 cm(2) s(-1) V(-1)), despite of the larger reorganization energy for hole transport in 2. The symmetric intrastack S...C contacts found between the thieno[3,2-b]thiophene and pyrimidinyl units explain the unique features of the crystal structure of 2 and the resulting large electronic coupling.