Dithienyl Acenedithiophenediones as New π-Extended Quinoidal Cores: Synthesis and Properties.

We have synthesized two isomeric pairs of benzo- and naphthodithiophenediones with two flanking thiophenes and characterized them by single-crystal X-ray analysis, cyclic voltammetry, steady-state optical electronic absorption and emission spectroscopies, transient absorption spectroscopy, and vibrational spectroscopies with in situ spectroelectrochemistry techniques, and then compared them with the thieno[3,2-b]thiophene-2,5-dione counterpart that we previously reported. The results show that the central acenedithiophenedione cores have quinoidal conjugation with closed-shell character. The π-extension of the quinoidal core raises (lowers) the HOMO (LUMO) energy levels of the triads, resulting in the drastic reduction of their energy gaps from approximately 2.0 eV to 1.1 eV. Owing to the electron-withdrawing nature of the carbonyl terminal group at the quinoidal core, the triads have low-lying LUMO energy levels ranging from -3.9 eV to -4.3 eV, and can be regarded as strong electron-acceptor building units. Interestingly, the pairs of structural isomers have similar electronic structures in both the neutral and charged states despite the different shapes (linear and angular) and/or symmetry (C2h and C2v ) of the acenedithiophenedione cores.

N,N'-Unsubstituted Naphthodithiophene Diimide: Synthesis and Derivatization via N-Alkylation and -Arylation.

An efficient and scalable method for the synthesis of N,N'-unsubstituted naphtho[2,3-b:6,7-b']dithiophene-4,5,9,10-tetracarboxylic diimide (NDTI) was newly developed, and the compound was utilized in the Mitsunobu reaction and copper-catalyzed coupling reaction with phenyl boronic acids to synthesize a range of N-alkyl- and phenyl-substituted NDTI derivatives. The new synthetic protocol to NDTI derivatives is advantageous over the previously reported one in terms of the amenability to large-scale synthesis and compatibility with the synthesis of a wide range of N-alkyl and phenyl derivatives, which can in turn pave the way to wide application of NDTI derivatives into electronic materials.

Soluble Dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene Derivatives for Solution-Processed Organic Field-Effect Transistors.

We demonstrate a new approach to solution-processable dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT) derivatives that can afford good thin-film transistors having mobilities higher than 0.1 cm(2) V(-1) s(-1). The key molecular design strategy is the introduction of one branched alkyl group at the edge of the DNTT core, which improves solubility while retaining semiconducting characteristics in the thin-film state. Dialkylation, i.e., the introduction of two branched alkyl groups on the DNTT core, had a detrimental effect on the semiconducting properties. Although the physicochemical properties of the mono- and dialkylated derivatives at the molecular level were almost the same, the thin-film absorption spectra and the ionization potentials (IPs) were markedly different, indicating that the intermolecular interaction in the thin-film state was affected by the number of alkyl groups. Indeed, the packing structures of the monoalkylated DNTTs in the thin-film state, which were estimated from the XRD patterns, were similar to that of parent DNTT, indicating the existence of the lamella structure with the herringbone packing motif. In sharp contrast, the XRD patterns of the dialkylated DNTT thin films showed poor crystallinity, and the packing structures were significantly different from that of parent DNTT. All the results of structural characterization in the thin-film state and evaluation of device characteristics of the DNTT derivatives with branched alkyl groups indicate that the introduction of a branched alkyl group in the molecular long-axis direction is an effective way to solubilize the rigid, largely π-extended organic semiconducting core without interfering with the semiconducting characteristics in the thin-film state.