Yuhi Inada

Nitrogen-doped graphitic carbon synthesized by laser annealing of sumanenemonoone imine as a bowl-shaped π-conjugated molecule.

Nitrogen-doped graphitic carbons (NGCs, Figure 1 a) have attracted much interest owing to their electrical and catalytic properties, thus leading to significant contributions toward their potential applications. Recently, many researchers have revealed one of the critical factors influencing their effectivities to be the bonding pattern of nitrogen atoms in the graphitic lattice. However, the composition ratio of nitrogen-to-carbon (N/C) is also a crucial parameter as the amount of doped nitrogen atoms determines the properties. Synthetic methods that allow rational control make the design of materials more efficient, thereby providing facile modulation and enhancement of the performance. The N/C ratio of the resulting NGC is controlled in most of the previously-reported syntheses, including direct synthesis such as chemical vapor deposition (CVD)-based, 20] segregation, and arc-discharge methods, and postsynthesis such as thermal, plasma, 28,29] hydrazine reduction, or laser treatment of graphene, graphene oxide (GO), or graphite with various nitrogen sources. However, it is necessary to adjust multiple parameters, determined by experiments, to control the N/C ratio. Therefore, we adopted an approach to transform nitrogen-containing carbonbased compounds with a fixed N/C ratio (as a starting material) into NGC, with the N/C ratio unchanged. Forming the graphitic skeleton of NGCs is often performed by pyrolysis using a furnace 33–44] or laser treatment. Although carbonization generally progresses with increasing temperature, most nitrogen atoms are diminished in the process when heated up above 600–800 8C. Therefore, to increase the degree of carbonization and to suppress loss of nitrogen atoms, a system favorable to carbonization has to be designed. Bowl-shaped compounds (hereinafter called by “p bowls”), which belong to nonplanar p-conjugated compounds, have also attracted significant interest. p Bowls are represented as partial structures of fullerene, including sumanene (1, C21H12, Figure 1 b), [56] corannulene (C20H10), [57] and so on. There have been limited studies on p bowls as compared to those on fullerenes and carbon nanotubes. Therefore, we have been actively researching sumanene chemistry to show the potential characteristics of p bowls. One of the features of p bowls is the strain attributed to the nonplanar p-conjugated shape (Figure 1 c). Because of the strain, we expected a C C bond of 1 to be cleaved with ease as compared to those of planar ones, and this might support the carbonization. Moreover, as mentioned above, laser is known as one of the heating sources that can locally promote carbonization owing to its photothermal effect, thus allowing a target to be rapidly heated with positional selectivity. Therefore, this method is considered to be attractive for potential applications such as in electronic devices. As for the other nonplanar p-conjugated compounds, a laser-induced conductivity increase of fullerene C60 has been reported. [59–62] If monolay[a] Y. Inada, Dr. T. Amaya, Y. Shimizu, Dr. A. Saeki, Prof. S. Seki, Prof. T. Hirao Department of Applied Chemistry Graduate School of Engineering, Osaka University Yamada-oka, Suita, Osaka 565-0871 ACHTUNGTRENNUNG(Japan) Fax: (+81) 6-6879-7415 E-mail : hirao@chem.eng.osaka-u.ac.jp [b] Dr. T. Otsuka, Dr. R. Tsuji KANEKA Fundamental Technology Research Alliance Laboratories Graduate School of Engineering, Osaka University Yamada-oka, Suita, Osaka 565-0871 ACHTUNGTRENNUNG(Japan) [c] Prof. T. Hirao JST, ACT-C, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012 (Japan) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/asia.201300500. Figure 1. (a) Our approach to synthesize nitrogen-doped graphitic carbon (gray: carbon, dark gray: nitrogen) from a nitrogen-containing strained compound. (b) Sumanene (1, C21H12) and sumanenemonoone imine (2, C28H17N). (c) Molecular structure of 1 based on X-ray crystallographic analysis: p-Conjugated plane is strained to be nonplanar.

Sumanenemonoone Imines Bridged by Redox-Active π-Conjugated Unit: Synthesis, Stepwise Coordination to Palladium(II), and Laser-Induced Formation of Nitrogen-Doped Graphitic Carbon

Sumanenemonoone imine compounds bridged by a redox-active π-conjugated unit on the basis of the conversion between 1,4-phenylenediamine and 1,4-benzoquinonediimine were synthesized and characterized. The stepwise coordination of the imino groups to Pd(II) in the sumanenemonoone imine compound bridged by 1,4-benzoquinonediimine was indicated by the titration experiment. Laser irradiation of a film of the metal-free quionediimine gave nitrogen-doped graphitic carbon, which was supported by an increase in conductivity and by Raman spectroscopy. The obtained graphitic carbon corresponds to carbonous compounds thermally treated at approximately 700-1000 °C. The ratio of nitrogen and carbon relative to that in the starting compound was nearly completely retained (5.4% decrease).

Investigation of thresholds in laser-induced carbonization of sumanene derivatives through in situ observation utilizing a Raman spectroscope

A useful method was demonstrated to investigate 532 nm laser energy threshold to carbonize various compounds including sumanene derivatives through in situ observation utilizing a micro-Raman spectrometer. It was revealed that the thresholds of sumanene derivatives are lower than those of the planar partial structures of sumanene derivatives. Moreover, [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) shows a considerably lower threshold than the sumanene derivatives utilizing this method. This work can be expected to contribute toward the evolution of laser-induced carbonization-based chemistry.

Design principle of high-performance organic single-crystal light-emitting devices

Organic semiconductor crystals exhibit unique optoelectronic characteristics such as high carrier mobility and laser oscillation. Nonetheless, it remains difficult thus far to achieve such potential activities on an optical device configuration mainly because of lack of knowledge of optical parameters such as refractive indices and their dispersion. Here, we demonstrate a simple but powerful design principle of high-performance organic single-crystal light-emitting devices. The method is based upon observation of emission-angle dependent spectra produced from an organic slab single crystal equipped with a one-dimensional diffraction grating. The emission spectra are characterized by sharply resolved lines whose locations are blueshifted or redshifted as a function of the emission angles. Detailed analysis of these emission lines has enabled us to solve equations of electromagnetic wave motion within and outside the slab crystal and to get solutions under appropriate boundary conditions. The design princip...

Organic crystal light-emitting transistors with top-gate configuration

We applied the top-gate configuration to organic light-emitting transistors (OLETs) having an organic semiconductor crystal and an aluminum-doped zinc oxide (AZO) layer. The AZO layer was inserted between a quartz substrate and the organic crystal. The devices had the top-contact configuration where gold and an alloy of magnesium and silver were used for the contacts. Silver and Parylene C® were used for a gate contact and a gate insulator for the top-gate configuration, respectively. These OLETs showed more efficient current injection at low voltages than both the devices without a gate contact and the devices having the bottom-gate configuration. The present results indicate that the top-gate configuration is effective for improving the crystal OLET characteristics.

Synthesis of phosphonic acid ring-substituted polyanilines via direct phosphonation to polymer main chains

Phosphonic acid ring-substituted polyanilines (PhosPANIs) were synthesized via reductive phosphonation of pernigraniline (a fully oxidized form of PANI) with P(OEt)3 and subsequent hydrolysis. The carbon–phosphorus bond formation was suggested from 31P NMR. This is the first example of direct phosphonation of PANI. The formal substitution ratio of the phosphonate to total number of phenyl rings in the polymer after the phosphonation reaction was up to 52%. The repetition of the phosphonation reaction procedure gave the diethyl PhosPANI (EtPhosPANI) with 73% substitution ratio. Hydrolysis of EtPhosPANIs afforded the desired PhosPANIs. The self-doping of the obtained PhosPANIs was clearly exhibited by ESR, XPS and UV-vis-NIR absorption spectroscopy. The drop-cast films of PhosPANIs showed electrical conductive properties with a level suitable for charge dissipation materials. The developed synthetic approach is considered to be valuable as a practical method for phosphonic acid self-doped conductive PANIs.

Organic crystal transistors with organic/inorganic hybrid electrodes

ABSTRACT We improved carrier injection of organic field-effect transistors (OFETs) by utilizing organic/inorganic hybrid electrodes. One of thiophene/phenylene co-oligomers (TPCOs) was employed as an organic semiconductor crystal layer and as a part of hybrid electrodes with Ag. As the volume ratio of Ag:TPCO changed from 1:0 to 1:3, the carrier mobility was enhanced up to ∼10−1 cm2/Vs even after exposure to the atmosphere. This value was 1.5 times larger than that of the OFET with electrodes made of only Ag, which suggests that the introduction of the hybrid electrodes improved the carrier injection from the electrode into the organic crystal.