Multifunctional π-expanded macrocyclic oligothiophene 6-mers and related macrocyclic oligomers.

Multifunctional π-expanded macrocyclic oligothiophene 6-mer 1, as well as 9- (2) and 12-mers (3), was synthesized using a McMurry coupling reaction as the key step. The 6-mer 1 was converted to cyclo[6](2,5-thienylene-ethynylene) (4) by using a bromination-dehydrobromination procedure. From X-ray analysis, the crystal structures of nonplanar 1 and round-shaped 2 and 4 were elucidated. STM showed that 4 formed a self-assembled monolayer at the liquid/solid interface to produce a hexagonal porous network. Chemical oxidation of 1, 2, and 4 with 1 and 2 equiv of Fe(ClO4)3 produced 1(•+) and 1(2+), 2(•+) and 2(2+), and 4(•+) and 4(2+), respectively. Although oligothiophene radical cations containing ß,ß-disubstituted thiophenes usually do not form π-dimers, 4(•+) clearly formed a π-dimer owing to its planar, round shape. As for the dications of 1, 2, and 4, 1(2+), which has 34π-electrons, exhibited a large diatropic ring current effect, whereas 34π dication 4(2+) only showed a medium diatropic ring current effect. In contrast to 1(2+) and 4(2+), 52π dication 2(2+) had biradical cationic character instead of Hückel-type cyclic conjugation. Interestingly, 6-mer 1 showed polymorphism and unusual melting point behavior due to the number of stable conformations in the solid state. Single crystals of 1 melted at 176 °C, whereas an amorphous film of 1 crystallized in the temperature range of 80-83 °C to form a lamellarly stacked microcrystalline film, which melted at 139 °C. The polymorphism of 1 was applied to either fluorescence switching or switching of field effect transistor (FET) activity and electrical conductivity.

Antiaromatic planar cyclooctatetraene: a strategy for developing ambipolar semiconductors for field effect transistors.

Tetra[2,3-thienylene] planarised by sulphur bridges and radially π-extended with (triisopropylsilyl)ethynyl groups had a narrow HOMO-LUMO gap due to the antiaromatic cyclooctatetraene core, and its single crystal FET device exhibited ambipolar characteristics with hole and electron mobilities of up to 0.40 and 0.18 cm(2) V(-1) s(-1), respectively.

Effects of the silicon core structures on the hole mobility of star-shaped oligothiophenes.

Star-shaped compounds with three or four oligothiophene units linked by an organosilicon core were prepared and their hole-transport capabilities were studied. A top-contact type thin film transistor (TFT) with a vapour-deposited film of tris[(ethylterthiophenyl)dimethylsilyl]methylsilane (3T(3)Si(4)) showed field-effect mobility (µ(FET)) of 4.4 × 10(-5) cm(2) V(-1) s(-1), while the device with the carbon centred analogue tris[(ethylterthiophenyl)dimethylsilyl]methane (3T(3)Si(3)C) showed no TFT activity. Intrinsic intramolecular hole mobility of 3T(3)Si(4) and 3T(3)Si(3)C was determined by time-resolved microwave conductivity measurements to be 8 × 10(-2) and 2 × 10(-2) cm(2) V(-1) s(-1), respectively, arising from higher degree of σ-π interaction in 3T(3)Si(4). To know more about the effects of the organosilicon core structures on the intermolecular hole mobility, we calculated internal reorganization energies for hole transfer at the (U)B3LYP/6-311+G(d,p)//(U)B3LYP/6-31G(d) level, which suggested smoother intermolecular charge transfer in the silicon derivative than the carbon and germanium analogues. Star-shaped compounds with quarterthiophene units behave in a different manner from the terthiophene derivatives and tris[(ethylquarterthiophenyl)dimethylsilyl]methane (4T(3)Si(3)C) showed higher TFT mobility of µ(FET) = 1.2 × 10(-3) cm(2) V(-1) s(-1) than its silicon analogue (4T(3)Si(4): µ(FET) = 5.4 × 10(-4) cm(2) V(-1) s(-1)). This is probably due to the more condensed packing of 4T(3)Si(3)C in the film, arising from the shorter Si-C bonding. Compounds with four terthiophene units were also prepared and tetrakis[(ethylterthiophenyl)-dimethylsilyl]silane (3T(4)Si(5)) showed the mobility of µ(FET) = 2.0 × 10(-4) cm(2) V(-1) s(-1), higher than that of 3T(3)Si(4), indicating the potential of tetrakis(oligothiophenyl) compounds as the TFT materials. Tetrakis[(ethylterthiophenyl)dimethylsilyl]germane (3T(4)Si(4)Ge) was less thermally stable and could not be processed to a film by vapour-deposition, but was found to be TFT active in the spin-coated film, although the mobility was rather low (µ(FET) = 7.7 × 10(-7) cm(2) V(-1) s(-1)).

2,7-Diphenyl[1]benzothieno[3,2-b]benzothiophene, a new organic semiconductor for air-stable organic field-effect transistors with mobilities up to 2.0 cm2 V(-1) s(-1).

Vapor-deposited thin films of a newly developed sulfur-containing heteroarene, 2,7-diphenyl[1]benzothieno[3,2-b][1]benzothiophene (DPh-BTBT), were used as an active layer of OFETs, which showed excellent FET characteristics in ambient conditions with mobilities of approximately 2.0 cm2 V-1 s-1 and Ion/Ioff of 107.

2,7-diphenyl[1]benzoselenopheno[3,2-b][1]benzoselenophene as a stable organic semiconductor for a high-performance field-effect transistor.

[1]Benzoselenopheno[3,2-b][1]benzoselenophene (BSBS) and its 2,7-diphenyl derivative (DPh-BSBS) were readily synthesized from diphenylacetylene and bis(biphenyl-4-yl)acetylene, respectively, with a newly developed straightforward selenocyclization protocol. In contrast to the parent BSBS that has poor film-forming properties, the diphenyl derivative DPh-BSBS formed a good thin film on the Si/SiO(2) substrate by vapor deposition. X-ray diffraction examination revealed that this film consists of highly ordered molecules that are nearly perpendicular to the substrate, making it suitable for use in the fabrication of organic field-effect transistors (OFETs). When fabricated at different substrate temperatures (room temperature, 60 degrees C, and 100 degrees C) in a "top-contact" configuration, all the DPh-BSBS-based OFET devices exhibited excellent p-channel field-effect properties with hole mobilities >0.1 cm(2) V(-1) s(-1) and current on/off ratios of approximately 10(6). This high performance was essentially maintained over 3000 continuous scans between V(g) = +20 and -100 V and reproduced even after storage under ambient laboratory conditions for at least one year.

2,6-Diarylnaphtho[1,8-bc:5,4-b'c']dithiophenes as new high-performance semiconductors for organic field-effect transistors.

A series of 2,6-diaryl-substituted naphtho[1,8-bc:5,4-b'c']dithiophene derivatives 2-6, whose aryl groups include 5-hexyl-2-thienyl, 2,2'-bithiophen-5-yl, phenyl, 2-naphthyl, and 4-biphenylyl, was synthesized by the palladium-catalyzed Suzuki-Miyaura coupling and utilized as active layers of organic field-effect transistors (OFETs). All devices fabricated using vapor-deposited thin films of these compounds showed typical p-type FET characteristics. The mobilities are relatively good and widely range from 10(-4) to 10(-1) cm2 V(-1) s(-1), depending on the substituent groups. Among them, the mobilities of the devices using films of 3-5 tend to increase with the increasing temperature of the Si/SiO2 substrate during film deposition. In particular, the device based on the naphthyl derivative 5, when fabricated at 140 degrees C, marked a high mobility of 0.11 cm2 V(-1) s(-1) with an on/off ratio of 10(5), which is a top class of performance among organic thin-film transistors. Studies of X-ray diffractograms (XRDs) have revealed that the film of 4 and 5 is composed of two kinds of crystal grains with different phases, so-called "single-crystal phase" and "thin film phase", and that the proportion of the thin film phase increases with an increase of the substrate temperature. In the thin film phase the assembled molecules stand nearly upright on the substrate in such a way as to be favorable to carrier migration.

2,6-Diphenylbenzo[1,2-b:4,5-b']dichalcogenophenes: a new class of high-performance semiconductors for organic field-effect transistors.

2,6-Diphenylbenzo[1,2-b:4,5-b']dichalcogenophenes including thiophene, selenophene, and tellurophene analogues as organic semiconductors for field-effect transistors were effectively synthesized in three steps from commercially available 1,4-dibromobenzene. All three benzodichalcogenophenes acted as good p-type semiconductors, and particularly the selenophene analogue, 2,6-diphenylbenzo[1,2-b:4,5-b']diselenophene, showed high FET mobility of 0.17 cm2 V-1 s-1.

Preparation of 4,4-diaryl-2-(tricyanoethenyl)dithienosiloles and vapor-chromic behavior of the film.

[reaction: see text] Reactions of 4,4-diphenyl- and 4,4-di(p-tolyl)dithienosilole with tetracyanoethene (TCNE) in DMF gave coupling products 4,4-diphenyl- and 4,4-di(p-tolyl)-2-(tricycanoethenyl)dithienosilole (1a and 1b) in good yield. The films of 1b exhibited vapor-chromism, and the color of the film changed from red to blue-purple upon exposure to the vapor of organic solvents such as ethanol, methanol, acetonitrile, ethyl acetate, acetone, and hexane. The color reverted to the original red upon contact with chloroform vapor, indicating that this process is reversible.