Structure and nanostructure in ionic liquids.

: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

3.2. Thienothiophenes 1216 3.2.1. Thieno[3,4-b]thiophene Analogues 1216 3.2.2. Thieno[3,2-b]thiophene Analogues 1217 3.2.3. Thieno[2,3-b]thiophene Analogues 1218 3.3. , ′-Bridged Bithiophenes 1219 3.3.1. Dithienothiophene (DTT) Analogues 1220 3.3.2. Dithieno[3,2-b:2′3′-d]thiophene-4,4-dioxides 1221 3.3.3. Dithienosilole (DTS) Analogues 1221 3.3.4. Cyclopentadithiophene (CPDT) Analogues 1221 3.3.5. Nitrogen and Phosphor Atom Bridged Bithiophenes 1222

Functional oligothiophenes: molecular design for multidimensional nanoarchitectures and their applications.

Ionic liquids in analytical chemistry.

One of the most important objectives in materials, chemical, and physical sciences is the creation of large conjugated macrocycles with well-defined shapes, since such molecules are not only theoretically and experimentally interesting but also have potential applications in nanotechnology. Fully unsaturated macrocycles are regarded as models for infinitely conjugated π systems with inner cavities, and exhibit unusual optical and magnetic behavior. Macrocycles have interior and exterior sites, and site-specific substitution at both or either site can afford attractive structures, such as 1D, 2D, and 3D supramolecular nanostructures. These nanostructures could be controlled through the use of π-extended large macrocycles by a bottom-up strategy. Numerous shape-persistent π-conjugated macrocycles have been synthesized, but only a few are on the nanoscale. This Review focuses on nanosized π-conjugated macrocycles (>1 nm diameter) and giant macrocycles (>2 nm diameter), and summarizes their syntheses and properties.

Conjugated macrocycles: concepts and applications.

Charge carrier control is a key issue in the development of electronic functions of semiconductive materials. Beyond the simple enhancement of conductivity, high charge carrier accumulation can realize various phenomena, such as chemical reaction, phase transition, magnetic ordering, and superconductivity. Electric double layers (EDLs), formed at solid-electrolyte interfaces, induce extremely large electric fields. This results in a high charge carrier accumulation in the solid, much more effectively than solid dielectric materials. In the present review, we describe recent developments in the field-effect transistors (FETs) with gate dielectrics of ionic liquids, which have attracted much attention due to their wide electrochemical windows, low vapor pressures, and high chemical and physical stability. We explain the capacitance effects of ionic liquids, and describe the various combinations of ionic liquids and organic and inorganic semiconductors that are used to achieve such effects as high transistor performance, insulator-metal transitions, superconductivity, and ferromagnetism, in addition to the applications of the ionic-liquid EDL-FETs in logic devices. We discuss the factors controlling the mobility and threshold voltage in these types of FETs, and show the ionic liquid dependence of the transistor performance.

Electric-double-layer field-effect transistors with ionic liquids.

Electrostatic carrier injection and electrochemical doping of octathio[8]circulene thin films is examined for six kinds of ionic liquids using in situ cyclic voltammetry (CV) and conductivity measurements. The frequency dependence of the capacitance measurements indicates that the ionic liquids form electric-double-layers (EDLs) below 102 Hz. The performance of the EDL-organic thin film transistors (OTFTs) of octathio[8]circulene demonstrates that the transistor carrier mobility shows a linear decrease with an increase in the capacitance of the ionic liquids. In contrast, the electrochemical oxidation potentials and the threshold voltage of the EDL-OTFT are governed only by one component of the ionic liquid; namely, the electrostatic and electrochemical hole injections are significantly affected by the anions.

Ionic-Liquid Component Dependence of Carrier Injection and Mobility for Electric-Double-Layer Organic Thin-Film Transistors

Carbon–sulfur compounds have been studied extensively as key materials in organic/molecular electronics. A variety of polyand oligothiophenes have been synthesized by organic synthesis and electrochemistry to elucidate their electronic properties. TTF (=1,4,5,8-tetrathiafulvalene) is a very important molecular skeleton as a donor for organic metals and superconductors; [TTF]ACHTUNGTRENNUNG[TCNQ (7,7,8,8-tetracyanoquinodimethane)] was the first organic metal to be developed into organic superconductors in the salts of TMTSF (= tetramethyltetraselenafulvalene), BEDT-TTF (bis(ethylenedithio)tetrathiafulvalene). In these materials, intermolecular S···S contacts play a crucial role in bringing about multidimensional electronic structures that are advantageous to electrical conduction. Cyclic oligothiophenes and thiocirculenes possess promising molecular structures from this perspective; the sulfur atoms are exposed to the outside of the molecular rings. Intermolecular S···S contacts are naturally expected in their crystals. In addition, their molecular structures are of considerable interest because they involve the radialene framework that has been a theoretical and experimental matter of concern with regard to exocyclic double bonds, aromaticity, and p-conjugation. Recently, Nenajdenko et al. synthesized octathio[8]circulene (2) from the parent compound, tetrathiophene (1), and 2 named “sulflower”. They obtained 2 as a red powder and estimated molecular and crystal structures from powder X-ray diffraction data, concluding the presence of a closed packing structure in the solid state with short intermolecular S···S contacts. Although the synthesis of 2 has attracted much attention, there is no single-crystal X-ray analysis; the molecular structure of 2 is open to debating on bond lengths, antiaromaticity. In our previous work, we carried out crystal growths and thin-film fabrications of a planar macrocyclic molecule, tetrakis(thiadiazole)porphyrazine, with strong self-assembling capabilities due to electrostatic S···N contacts and p–p interactions. The investigations revealed a highly ordered molecular arrangement in the thin films, which is nearly the same as that in the bulk crystals. In the present work, we prepared the single crystals and thin films of the sulflower 2. The molecular, crystal, and thin-film structures of 2 are described in detail, on the basis of the results of X-ray singlecrystal analysis, in comparison with those of 1. Single crystals of the parent compound 1 were grown by slow evaporation of the Et2O solution at room temperature. While the X-ray structure of 1 has been reported previously, we obtained a new polymorph belonging to the monoclinic P21/c space group. [17] In this new polymorph, there are two crystallographically independent molecules, whereas their molecular structures are nearly the same. Figure 1 shows top and side views of one of the two molecules. The bond lengths of 1 are shown in Figure S1 (Supporting Information) and Table 1, where the endo bond is the one shared

Molecular, Crystal, and Thin-Film Structures of Octathio[8]circulene: Release of Antiaromatic Molecular Distortion and Lamellar Structure of Self-Assembling Thin Films

We studied the electrochemistry of the thin films of octathio[8]circulene (1) in an ionic liquid, N,N-diethyl-N-methyl(2-methoxyethyl) ammonium bis(trifluoromethylsulfonyl)imide (DEME-TFSI). The compound 1 exhibited simultaneous two-electron oxidation in the oxidation scan and then stepwise reductions to the original neutral state, showing significant electrochromism. This color change was well-interpreted in terms of the n−π transition that is allowed by the vacancy in the HOMO of 1 after electrochemical oxidation.

Electrochemical and electrochromic properties of octathio[8]circulene thin films in ionic liquids.

Dual-gate organic thin-film transistors (OTFTs) of octathio[8]circulene (1) with ionic liquid and SiO2 gate dielectrics lead to good transistor performance with a high on/off ratio (∼105), a low threshold voltage (∼−5 V), a low subthreshold slope (∼150 mV/decade), and low power operation, thus surpassing the performance of the single-gate OTFTs of 1. This operation is a promising method for improving the carrier concentrations in OTFTs and for realizing high-performance OTFTs.

Takuya Fujimoto

Papers

Electric-double-layer field-effect transistors with ionic liquids.

Ionic-Liquid Component Dependence of Carrier Injection and Mobility for Electric-Double-Layer Organic Thin-Film Transistors

Molecular, Crystal, and Thin-Film Structures of Octathio[8]circulene: Release of Antiaromatic Molecular Distortion and Lamellar Structure of Self-Assembling Thin Films

Electrochemical and electrochromic properties of octathio[8]circulene thin films in ionic liquids.

Dual-gate field-effect transistors of octathio[8]circulene thin-films with ionic liquid and SiO2 gate dielectrics