Atsushi Kimoto

Electron spin resonance observation of field-induced charge carriers in ultrathin-film transistors of regioregular poly(3-hexylthiophene) with controlled in-plane chain orientation

Ultrathin-film polymeric transistors with controlled in-plane chain orientation have been fabricated based on Langmuir–Blodgett technique by cospreading liquid crystal molecule with regioregular poly(3-hexylthiophene). The mobilities parallel to the chain direction reached 0.001–0.01 cm2/V s for 1 to 5 monolayer thick transistors. Mobility ratio was about 2 for the parallel and perpendicular directions. Electron spin resonance (ESR) signals of the field-induced polarons exhibited clear in-plane anisotropies due to unpaired π-electrons. The anisotropic ESR spectra together with the optical dichroism determine the detailed molecular orientations in the channel of such ultrathin transistors.

In Situ KPFM Imaging of Local Photovoltaic Characteristics of Structured Organic Photovoltaic Devices

Here, we discuss the local photovoltaic characteristics of a structured bulk heterojunction, organic photovoltaic devices fabricated with a liquid carbazole, and a fullerene derivative based on analysis by scanning kelvin probe force microscopy (KPFM). Periodic photopolymerization induced by an interference pattern from two laser beams formed surface relief gratings (SRG) in the structured films. The surface potential distribution in the SRGs indicates the formation of donor and acceptor spatial distribution. Under illumination, the surface potential reversibly changed because of the generation of fullerene anions and hole transport from the films to substrates, which indicates that we successfully imaged the local photovoltaic characteristics of the structured photovoltaic devices. Using atomic force microscopy, we confirmed the formation of the SRG because of the material migration to the photopolymerized region of the films, which was induced by light exposure through photomasks. The structuring technique allows for the direct fabrication and the control of donor and acceptor spatial distribution in organic photonic and electronic devices with minimized material consumption. This in situ KPFM technique is indispensable to the fabrication of nanoscale electron donor and electron acceptor spatial distribution in the devices.

Donor–acceptor-Type Polymers Based on Dithieno[2,3-b;7,6-b]carbazole Unit for Photovoltaic Applications

Dithieno[2,3-b;7,6-b]carbazole (TCZT), a type of heteropentacene with nitrogen and sulfur atoms, was synthesized with a focus on the unique reactivity of carbazole via double intramolecular Friedel-Crafts acylation. A donor-acceptor-type polymer (PTCZTBT) was also synthesized, and its physicochemical properties are reported.

Unusual Side‐Chain Effects on Charge‐Carrier Lifetime in Discotic Liquid Crystals

When hexa-peri-hexabenzocoronene (HBC) carries paraffinic side chains with ester-ether termini (1a-1c), a hexagonal columnar liquid-crystalline (LC) mesophase forms, which is characterized by a very wide temperature range (ca. 0-300 degrees C). The LC materials from these HBC derivatives show characteristic electronic properties with an extremely long photocarrier lifetime. For example, by means of a flash-photolysis time-resolved microwave conductivity technique, the photocarrier lifetime, observed for liquid-crystalline 1a, is as long as 14 ms, which is four-orders of magnitude longer than that of fully paraffinic HBC 4 (0.0011 ms). The maximum transient photoconductivities of liquid-crystalline 1a-1c are comparable to one another and also to those of HBCs without ester-ether terminals. Liquid-crystalline 1a exhibits an obvious photocurrent generation in response to light illumination.

Formation of hexaarylbiimidazole heterodimers via the cross recombination of two lophyl radicals

The formation of hexaarylbiimidazole heterodimers has been investigated in detail by X-ray crystallography and 1H NMR spectroscopy.

Design and synthesis of an amphiphilic graft hydrogel having a hydrophobic domain formed by multiple interactions.

A novel hydrogel having hydrophobic oligo segments and hydrophilic poly(acrylamidoglycolic acid) (PAGA) as pH responsive polymer segments was designed and synthesized to be used as a soft biomaterial. Poly(trimethylene carbonate) (PTMC) as the side chain, for which the degrees of polymerization were 9, 19, and 49, and the composition ratios were 1, 5, and 10mol%, was used as the oligo segment in the hydrogel. The swelling ratio of the hydrogel was investigated under various changes in conditions such as pH, temperature, and hydrogen bonding upon urea addition. Under pH2-11 conditions, the graft gel reversibly swelled and shrank due to the effect of PAGA main chain. The interior morphology and skin layer of the hydrogel was observed by a scanning electron microscope. The hydrogel composed of PAGA as the hydrophilic polymer backbone had a sponge-like structure, with a pore size of approximately 100μm. On the other hand, upon increasing the ratio of trimethylene carbonate (TMC) units in the hydrogel, the pores became smaller or disappeared. Moreover, thickness of the skin layer significantly increased with the swelling ratio depended on the incorporation ratios of the PTMC macromonomer. Molecular incorporation in the hydrogel was evaluated using a dye as a model drug molecule. These features would play an important role in drug loading. Increasing the ratio of TMC units favored the adsorption of the dye and activation of the incorporation behavior.