Dithiophene-Fused Tetracyanonaphthoquinodimethanes (DT-TNAPs): synthesis and characterization of π-extended quinoidal compounds for n-channel organic semiconductor.

Dithiophene-fused tetracyanonaphthoquinodimethanes (DTTNAPs) were synthesized and evaluated as n-channel organic semiconductors. DTTNAPs, regardless of isomeric structures and substituents, have low-lying LUMO energy levels (∼4.6 eV below the vacuum level), suitable for stable n-channel field-effect transistors (FETs) under ambient conditions. In fact, α-DTTNAP derivatives afforded solution-processed FETs showing an electron mobility of 10(-3) cm(2) V(-1) s(-1), indicating that DTTNAPs are a potential molecular framework for n-channel organic semiconductors.

Borylation on benzo[1,2-b:4,5-b']- and naphtho[1,2-b:5,6-b']dichalcogenophenes: different chalcogene atom effects on borylation reaction depending on fused ring structure.

The direct borylation reactions of two types of α-silyl-protected acenedichalcogenophenes, i.e., benzo[1,2-b:4,5-b']- and naphtho[1,2-b:5,6-b']dichalcogenophenes, were examined, and it was observed that the reaction efficiency largely depends on the fused ring structure and chalcogenophene ring.

Orthogonally functionalized naphthodithiophenes: selective protection and borylation.

Selective functionalization protocols of naphtho[1,2-b;5,6-b']dithiophene (NDT3) by combining protection of the thiophene α-positions and direct borylation on the naphthalene core are described, which allows synthesizing a number of new NDT3-based building blocks with various substituents and isomeric NDT3-based polymers with different main chain structures. The same protocol is applicable to other isomeric naphthodithiophenes (NDTs), which affords a set of key building blocks for the development of elaborated functional π-materials.

Angular-shaped naphthodifurans, naphtho[1,2-b;5,6-b']- and naphtho[2,1-b;6,5-b']-difuran: are they isoelectronic with chrysene?

Although angular-shaped naphthodifurans, naphtho[1,2-b;5,6-b']- and naphtho[2,1-b;6,5-b']-difuran, are formally isoelectronic with chrysene as their thiophene counterparts, naphtho[1,2-b;5,6-b']- and naphtho[2,1-b;6,5-b']-dithiophene, the HOMO energy level of naphthodifurans is much higher than those of naphthodithiophenes and chrysene. The difference in electronic structure in the ground state can be explained by distinct electronic perturbation from the outermost aromatic rings.

Thienoacene-based organic semiconductors.

Thienoacenes consist of fused thiophene rings in a ladder-type molecular structure and have been intensively studied as potential organic semiconductors for organic field-effect transistors (OFETs) in the last decade. They are reviewed here. Despite their simple and similar molecular structures, the hitherto reported properties of thienoacene-based OFETs are rather diverse. This Review focuses on four classes of thienoacenes, which are classified in terms of their chemical structures, and elucidates the molecular electronic structure of each class. The packing structures of thienoacenes and the thus-estimated solid-state electronic structures are correlated to their carrier transport properties in OFET devices. With this perspective of the molecular structures of thienoacenes and their carrier transport properties in OFET devices, the structure-property relationships in thienoacene-based organic semiconductors are discussed. The discussion provides insight into new molecular design strategies for the development of superior organic semiconductors.

Dianthra[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DATT): synthesis, characterization, and FET characteristics of new π-extended heteroarene with eight fused aromatic rings.

A novel highly π-extended heteroarene with eight fused aromatic rings, dianthra[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DATT), was selectively synthesized via a newly developed synthetic strategy, fully characterized by means of single crystal X-ray structural analysis, and examined as an organic semiconductor in thin film transistors. Even with its highly extended acene-like π-system, DATT is a fairly air-stable compound with IP of 5.1 eV. Single crystal X-ray structural analysis revealed its planar molecular structure and the lamella-like layered structure with typical herringbone packing. Theoretical calculations of the solid state electronic structure based on the bulk single crystal structure suggest that DATT affords almost comparable intermolecular orbital couplings between HOMOs (t(HOMO)) with those of dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT), implying its good potential as an organic semiconductor for organic field-effect transistors. In fact, field-effect mobilities as high as 3.0 cm(2) V(-1) s(-1) were achieved with vapor-processed DATT-based devices, which is comparable with that of DNTT-based devices. The molecular ordering of DATT in the thin film state, however, turned out to be not completely uniform; as elucidated by in-plane and out-of-plane XRD measurements, the face-on molecular orientation was contaminated in the edge-on orientation, the former of which is not optimal for efficient carrier transport and thus could limit the mobility.

Impact of isomeric structures on transistor performances in naphthodithiophene semiconducting polymers.

Four isomeric naphthodithiophenes (NDTs) with linear and angular shapes were introduced into the polythiophene semiconductor backbones, and their field-effect transistor performances were characterized. The polymers bearing naphtho[1,2-b:5,6-b']dithiophene (NDT3), an angular-shaped NDT, exhibited the highest mobilities of ∼0.8 cm(2) V(-1) s(-1) among the four NDT-based polymers, which is among the highest reported so far for semiconducting polymers. Interestingly, the trend of the mobility in the NDT-based polymers was contrary to our expectations; the polymers with angular NDTs showed higher mobilities than those with linear NDTs despite the fact that naphtho[2,3-b:6,7-b']dithiophene (NDT1), a linear-shaped NDT, has shown the highest mobility in small-molecule systems. X-ray diffraction studies revealed that angular-NDT-based polymers gave the highly ordered structures with a very close π-stacking distance of 3.6 Å, whereas linear-NDT-based polymers had a very weak or no π-stacking order, which is quite consistent with the trend of the mobility. The nature of such ordering structures can be well understood by considering their molecular shapes. In fact, a linear NDT (NDT1) provides angular backbones and an angular NDT (NDT3) provides a pseudostraight backbone, the latter of which can pack into the highly ordered structure and thus facilitate the charge carrier transport. In addition to the ordering structure, the electronic structures seem to correlate with the carrier transport property. MO calculations, supported by the measurement of ionization potentials, suggested that, while the HOMOs are relatively localized within the NDT cores in the linear-NDT-based polymers, those are apparently delocalized along the backbone in the angular-NDT-based polymers. The latter should promote the efficient HOMO overlaps between the polymer backbones that are the main paths of the charge carrier transport, which also agrees with the trend of the mobility. With these results, we conclude that angular NDTs, in particular NDT3, are promising cores for high-performance semiconducting polymers. We thus propose that both the molecular shapes and the electronic structures are important factors to be considered when designing high performance semiconducting polymers.

Linear- and angular-shaped naphthodithiophenes: selective synthesis, properties, and application to organic field-effect transistors.

A straightforward synthetic approach that exploits linear- and angular-shaped naphthodithiophenes (NDTs) being potential as new core structures for organic semiconductors is described. The newly established synthetic procedure involves two important steps; one is the chemoselective Sonogashira coupling reaction on the trifluoromethanesulfonyloxy site over the bromine site enabling selective formation of o-bromoethynylbenzene substructures on the naphthalene core, and the other is a facile ring closing reaction of fused-thiophene rings from the o-bromoethynylbenzene substructures. As a result, three isomeric NDTs, naphtho[2,3-b:6,7-b']dithiophene, naphtho[2,3-b:7,6-b']dithiophenes, and naphtho[2,1-b:6,5-b']dithiophene, are selectively synthesized. Electrochemical and optical measurements of the parent NDTs indicated that the shape of the molecules plays an important role in determining the electronic structure of the compounds; the linear-shaped NDTs formally isoelectronic with naphthacene have lower oxidation potentials and more red-shifted absorption bands than those of the angular-shaped NDTs isoelectronic with chrysene. On the contrary, the performance of the thin-film-based field-effect transistors (FETs) using the dioctyl or diphenyl derivatives were much influenced by the symmetry of the molecules; centrosymmetric derivatives tend to give higher mobility (up to 1.5 cm(2) V(-1) s(-1)) than axisymmetric ones (∼0.06 cm(2) V(-1) s(-1)), implying that the intermolecular orbital overlap in the solid state is influenced by the symmetry of the molecules. These results indicate that the present NDT cores, in particular the linear-shaped, centrosymmetric naphtho[2,3-b:6,7-b']dithiophene, are promising building blocks for the development of organic semiconducting materials.

High-mobility semiconducting naphthodithiophene copolymers.

We have designed and synthesized novel semiconducting polymers by introducing naphtho[1,2-b:5,6-b']dithiophene (NDT) into the polythiophene backbone. These polymers, which have a highly pi-extended heteroarene unit, achieved mobilities (>0.5 cm(2) V(-1) s(-1)) that are among the highest recorded to date for semiconducting polymers and most probably result from the highly ordered thin-film structures with crystalline close pi stacking. It is noteworthy that the choice of isomeric heteroarenes in the unit can dramatically change the physical and electronic structures and hence the OFET performance of the semiconducting polymers, even though the two isomers possess similar electronic structures; interestingly, this contrasts with the trend in small-molecule systems. We believe that these findings will give new insight into the design of new organic semiconducting materials and that the present polymers are promising materials for printable electronics.

Synthesis, properties, crystal structures, and semiconductor characteristics of naphtho[1,2-b:5,6-b']dithiophene and -diselenophene derivatives.

In this paper we present the synthesis, structures, characterization, and applications to field-effect transistors (FETs) of naphtho[1,2-b:5,6-b']dithiophene (NDT) and -diselenophene (NDS) derivatives. Treatment of 1,5-dichloro-2,6-diethynylnaphthalenes, easily derived from commercially available 2,6-dihydroxynaphthalene, with sodium chalcogenide afforded a straightforward access to NDTs and NDSs including the parent and dioctyl and diphenyl derivatives. Physicochemical evaluations of NDT and NDS derivatives showed that these heteroarenes have a similar electronic structure with isomeric [1]benzothieno[2,3-b][1]benzothiophene (BTBT) and [1]benzoselenopheneno[2,3-b][1]benzoselenophene (BSBS) derivatives, respectively. Although attempts to fabricate solution-processed field-effect transistors (FETs) with soluble dioctyl-NDT (C(8)-NDT) and -NDS (C(8)-NDS) failed, diphenyl derivatives (DPh-NDT and DPh-NDS) afforded vapor-processed FETs showing field-effect mobility as high as 0.7 cm(2) V(-1) s(-1). These results indicated that NDT and NDS are new potential heteroarene core structures for organic semiconducting materials.

One-pot synthesis of benzo[b]thiophenes and benzo[b]selenophenes from o-halo-substituted ethynylbenzenes: convenient approach to mono-, bis-, and tris-chalcogenophene-annulated benzenes.

A convenient one-pot procedure for the synthesis of benzo[b]thiophenes and selenophenes from readily available o-halo-ethynylbenzene precursors is described. Regardless of the substituent on the acetylene terminus or the number of cyclization moieties on the precursors, various benzo[b]thiophenes and selenophenes, including not only the parent, alkyl-, and phenyl-substituted derivatives but also benzo[1,2-b:4,5-b']dithiophenes and diselenophenes and benzo[1,2-b:3,4-b':5,6-b'']trithiophenes and triselenophenes can be prepared in good to high yields.