Solvent-dispersed benzothiadiazole-tetrathiafulvalene single-crystal nanowires and their application in field-effect transistors.

A new organic semiconductor (BT-TTF) based on molecular moieties of benzothiadiazole and tetrathiafulvalene was designed and synthesized, and its structure, molecular packing and charge-transporting properties were determined. Thermal properties, electrochemical behaviors, and optical absorption of this molecule were studied by using differential scanning calorimetry/thermal gravimetric analysis, cyclic voltammetry, and ultraviolet-visible spectroscopy, respectively. Its bulk and nanowire single crystals were prepared and characterized by X-ray crystallography, scanning electron microscopy, transmission electron microscopy, and field-effect transistors. It is found that short intermolecular S···S (3.41 Å), S···C (3.49 Å), and S···N (3.05 Å) contacts define the solid-state structure of BT-TTF single crystals which π-stack along the [100] with interplanar distances of 3.49 Å. Solvent-cast single-crystal nanowire transistors showed mobilities as large as 0.36 cm2/(V s) with current on/off ratios of 1×10(6). This study further illustrates the impact of molecular design and a demonstration of high-performance single-crystal nanowire transistors from the resulting semiconductor.

Patterning of robust self-assembled n-type hexaazatrinaphthylene-based nanorods and nanowires by microcontact printing.

The one-dimensional (1-D) self-assembly property of an n-type hexaazatrinaphthylene (HATNA) discotic pi-conjugated molecule was studied. Structurally robust unimolecular columnar stacks of HATNA with tunable length have been fabricated through a combination of supramolecular self-assembly and post-polymerization approach. Moreover, microcontact printing can be utilized to transfer the self-assembled nanostructures to the surface to create desired functional patterns.

Isolation and crystal structures of two singlet bis(triarylamine) dications with nonquinoidal geometries.

We report the first structural data for bis(diarylamine) "bipolarons": we have isolated and crystallographically characterized salts of the dications obtained by two-electron oxidation of E-4,4'-bis[di(p-anisyl)amino]stilbene and E,E-2,5-bis{4-[di(p-anisyl)amino]styryl}-3,4-di(n-butoxy)thiophene, [1](2+) and [2](2+) respectively. ESR, NMR, and magnetometry suggest both species have singlet ground states. X-ray structures, together with (1)H NMR coupling constants for [2](2+), indicate geometries in which the bond lengths are shifted toward a quinoidal pattern relative to that in the neutral species, but not to a fully quinoidal extent. In particular, the bond-length alternations across the vinylene bridging groups approach zero. DFT calculations with closed-shell singlet configurations reproduce the observed structures well. Our results indicate that singlet species for which one might expect quinoidal geometries (with differences of ca. 0.1 A between formally single and double bonds) on the basis of a limiting valence-bond representation of the structure can, in fact, show structures with significantly different patterns of bond lengths.

Intervalence transitions in the mixed-valence monocations of bis(triarylamines) linked with vinylene and phenylene-vinylene bridges.

(E)-4,4'-Bis[bis(4-methoxyphenyl)amino]stilbene, 1, (E,E)-1,4-bis[4-[bis(4-methoxyphenyl)amino]styryl]benzene, 2, and two longer homologues, (E,E,E)-4,4'-bis[4-[bis(4-methoxyphenyl)amino]styryl]stilbene, 3, and (E,E,E,E)-1,4-bis(4-[4-[bis(4-methoxyphenyl)amino]styryl]styryl)benzene, 4, have been oxidized to their mono- and dications using tris(4-bromophenyl)aminium hexachloroantimonate. The intervalence charge-transfer (IVCT) band of 1(+) is narrow and asymmetric and exhibits only weak solvatochromism. Analysis of this band indicates that 1(+) is a class-III or class-II/III borderline mixed-valence species. In contrast, a broad, strongly solvatochromic IVCT band is observed for 2(+), indicating that this species is a class-II mixed-valence species. The assignment of 1(+ ) and 2(+) as symmetric class-III and unsymmetric class-II species, respectively, is also supported by AM1 calculations. Hush analysis of the IVCT bands of both 1(+) and 2(+) gives larger electronic couplings, V, than for their analogues in which the double bonds are replaced with triple bonds. The diabatic electron-transfer distance, R, in 1(+) can be estimated by comparison of the V estimated by Hush analysis and from the IVCT maximum; it is considerably less than the geometric N-N separation, a result supported by quantum-chemical estimates of R for 1(+)-4(+). In 3(+) and 4(+), the IVCT is largely obscured by an intense absorption similar to a band seen in the corresponding dications and to that observed in the monocation of a model compound, (E,E,E)-1-[bis(4-methoxyphenyl)amino]-4-[4-[4-(4-tert-butylstyryl)styryl]styryl]benzene, 5, containing only one nitrogen redox center; we attribute this band to a bridge-to-N(+) transition. The corresponding dications 1(2+)-4(2+) show a complementary trend in the coupling between redox centers: the shortest species is diamagnetic, while the dication with the longest bridge behaves as two essentially noninteracting radical centers.

A mixed-valence bis(diarylamino)stilbene: crystal structure and comparison of electronic coupling with biphenyl and tolane analogues.

The E-4,4'-bis[di(p-anisyl)amino]stilbene cation is a class-III mixed-valence species with electronic coupling comparable to that in its biphenyl-bridged analogue, whereas its tolane-bridged analogue belongs to class II.