Kenta Goto

The synthesis, crystal structure and charge-transport properties of hexacene

Acenes can be thought of as one-dimensional strips of graphene and they have the potential to be used in the next generation of electronic devices. However, because acenes larger than pentacene have been found to be unstable, it was generally accepted that they would not be particularly useful materials under normal conditions. Here, we show that, by using a physical vapour-transport method, platelet-shaped crystals of hexacene can be prepared from a monoketone precursor. These crystals are stable in the dark for a long period of time under ambient conditions. In the crystal, the molecules are arranged in herringbone arrays, quite similar to that observed for pentacene. A field-effect transistor made using a single crystal of hexacene displayed a hole mobility significantly higher than that of pentacene. This result suggests that it might be instructive to further explore the potential of other higher acenes.

Photoinduced Color Change and Photomechanical Effect of Naphthalene Diimides Bearing Alkylamine Moieties in the Solid State

Photoinduced color change of naphthalene diimides (NDIs) bearing alkylamine moieties has been observed in the solid state. The color change is attributed to the generation of a NDI radical-anion species, which may be formed through a photoinduced electron-transfer process from the alkylamine moiety to the NDI. The photosensitivity of NDIs is highly dependent on the structures of the alkylamine moieties. Crystallographic analysis, kinetic analysis, UV/Vis/NIR spectroscopic measurements, and analysis of the photoproduct suggested that a radical anion was formed through an irreversible process initiated by proton abstraction between an amine radical cation and the neutral amine moiety. The radical anions formed stacks including mixed-valence stacks and radical-anion stacks, as shown by the broad absorption bands in near-IR spectra. These photosensitive NDIs also showed crystal bending upon photoirradiation, which may be associated with a change in the intermolecular distance of the NDI stacks by the formation of monomeric radical anions, mixed-valence stacks, and radical-anion stacks.

A novel hindered macrocyclic tetramine containing two bispidine units. A new type of proton sponge

Abstract A novel cyclam-like macrocyclic tetramine 1a was synthesized via coupling of bispidine and its bis(α-chloroacetamide) followed by reduction. Strongly basic but encrypted nitrogens of 1a were found to abstract a proton from chloroform to form dichlorocarbene.

Synthesis, structure, and electronic and photophysical properties of two- and three-layered [3.3]Paracyclophane-based donor-acceptor systems (1)

The synthesis, structural, redox, and photophysical properties of the two- and three-layered donor-acceptor (D-A) type [3.3]paracyclophanes ([3.3]PCPs) are described. The synthesis of the two- and three-layered [3.3]PCPs 1 and 2 containing 2,1,3-benzothiadiazole (BTD) as an acceptor was achieved by the (p-ethylbenzenesulfonyl)methyl isocyanide coupling method. The cyclic voltammograms of 1 and 2 along with those of respective dione precursors 5 and 7 clearly indicate that the presence of the -CH(2)COCH(2)- bridge interferes with the electronic interactions between the BTD and the benzene rings, suggesting the importance of the through-bond interaction in the ground state. In sharp contrast, the UV/vis spectra of 1 and 5 as well as those of 2 and 7 exhibit similar bands regardless of the presence of the -CH(2)COCH(2)- or -CH(2)CH(2)CH(2)- bridges, indicating that the charge-transfer (CT) interaction is mainly responsible for the through-space interaction. The two-layered PCPs, 5 and 1, show broad structureless fluorescence bands at the same position of 468 nm, while those of the three-layered PCPs, 7 and 2, appear at 501 and 496 nm, respectively, with lower quantum yields compared to those of the two-layered PCPs probably due to the stronger intramolecular CT interaction of the three-layered PCPs in the ground state.

Dynamic characteristics model of bi-directional DC-DC converter using state-space averaging method

In the fields of using green energy such as EV power system and the PV system, the bi-directional DC-DC converter, which is used to control the charge and discharge of batteries, is now attracting more and more attention. In the bi-directional DC-DC converter for the battery charger, the response characteristics and stability of one are key points for the performance of the whole system. However, it is complex to analyze the dynamic characteristics and control design, because both of forward direction mode and reverse direction mode of the converter have to be considered. In this paper, the simplified dynamic model of the bi-directional DC-DC converter is presented. Transfer functions of the converter are derived by using the state-space averaging method. And, the frequency characteristics of the converter for both of buck mode and boost mode are discussed. Finally, experimental results are shown to confirm the validity of the proposed dynamic model of the converter.

Substituent effect on the crystal packing and electronic coupling of tetrabenzocoronenes: a structure–property correlation

Tetrabenzo[a,d,j,m]coronene (TBC) is a contorted polyaromatic molecule which shows near co-facial π–π stacking in the crystalline state and the high electronic coupling resulting from the packing renders it a potential candidate as a transistor material. Substitution at the periphery perturbs the packing due to steric as well as dipolar interactions and thus changes the electronic coupling between neighbouring molecules. In the light of the high sensitivity of charge mobility toward electronic coupling, a new series of TBC derivatives with substituents at 1-, 2-, 3-, 6-, 7-, 8-positions were designed, synthesized, and characterized. Needle-like single crystals were prepared using the physical vapor transport (PVT) method for these unsymmetrically substituted derivatives and were used for crystal structure analyses as well as the single crystal field-effect transistor (SCFET) device fabrication. The derivatives with fluoro-containing substituents exhibit anti-parallel cofacial or slightly shifted π–π stacking, whereas those with bulky alkyl substituents show skewed and more significantly shifted π–π stacking. A systematic comparison of the crystal packings and the calculated electronic couplings/charge mobilities with the measured SCFET mobilities shows a rough correlation and sheds light on the origin of the large hole-mobility of the SCFET with hexa-fluorinated TBC as the channel material.

Synthesis, Optical Properties, and Electronic Structures of Tetrakis(pentafluorophenyl)tetrathiaisophlorin Dioxide

The synthesis, structure, optical and redox properties, and electronic structure of tetrakis(pentafluorophenyl)tetrathiaisophlorin dioxide (12) are reported. Oxidation of tetrakis(pentafluorophenyl)tetrathiaisophlorin (11) with dimethyldioxirane afforded the oxidized product, which was the tetrathiaisophlorin with two thiophene 1-oxide moieties (12). More significant nonplanarity and greater bond length alternation in 12 than those of 11 were observed by X-ray structural analysis. The absorption spectrum of 12 contains two bands at λ=348 and 276 nm, with a weak tail that extends to λ≈650 nm. Analysis of the magnetic circular dichroism spectrum of 12, based on Michls 4N-perimeter model and molecular orbital calculations, indicate that the broad band at λ=348 nm appears to contain N2 and P2 bands, and 12 is classified as a 4nπ system, similar to 11. The nuclear-independent chemical shift values and (1) H NMR spectroscopy data indicate that 12 has more antiaromatic character than 11.

Changing the volume of a giant macrocycle: the swelling of the macrocycle with organic solvents

The novel tetrahedral macrocycles 1a-1c have been synthesized. Macrocycles 1a and 1c were revealed to have the property to increase in volume in solution by complexation between the macrocycle and the solvent molecules.

Blue Fluorescence from BF2 Complexes of N,O-Benzamide Ligands: Synthesis, Structure, and Photophysical Properties

Small molecules having intense luminescence properties are required to promote biological and organic material applications. We prepared five types of benzamides having pyridine, pyridazine, pyrazine, and pyrimidine rings and successfully converted them into three types of the difluoroboronated complexes, Py@BAs, as novel blue fluorophores. Py@BA having a pyridine moiety (2-Py@BA) showed no fluorescence in solution, whereas Py@BAs of pyridazine and pyrazine moieties (2,3-Py@BA and 2,5-Py@BA, respectively) emitted blue fluorescence with quantum yields of ca. 0.1. Transient absorption measurements using laser flash photolysis of the Py@BAs revealed the triplet formation of 2,3- and 2,5-Py@BAs, while little transient signal was observed for 2-Py@BA. Therefore, the deactivation processes from the lowest excited singlet state of fluorescent 2,3- and 2,5-Py@BAs consist of fluorescence and intersystem crossing to the triplet state while that of the nonfluorescent Py@BA is governed almost entirely by internal conversion to the ground state. Conversely, in the solid state, 2-Py@BA emitted intense fluorescence with a fluorescence quantum yield as high as 0.66, whereas 2,3- and 2,5-Py@BAs showed fluorescence with quantum yields of ca. 0.2. The crystal structure of 2-Py@BA took a herringbone packing motif, whereas those for 2,3- and 2,5-Py@BAs were two-dimensional sheetlike. On the basis of the difference in crystal structures, the emission mechanism in the solid state was discussed.

Selective alcohol adsorption in a uniformly ordered array of lipophilic mesopores by a giant macrocycle

The crystal structure of giant macrocycle 1 was found to have a mesoporous structure. The lipophilic pores of 1 uniformly formed in an ordered array, and contributed to the selective adsorption of 1-BuOH among the isomers of butanol.