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Yoshii R.,Kyoto University | Yamane H.,Kyoto University | Nagai A.,Institutes for Molecular Science | Tanaka K.,Kyoto University | And 3 more authors.
Macromolecules | Year: 2014

We present efficient electron-transport materials based of polymers. π-Conjugated copolymers composed of boron dipyrromethene (BODIPY) or Aza-BODIPY were synthesized via the efficient Suzuki-Miyaura cross-coupling reaction of (2,5-bis(2-(2-(2-(pyridin-2-yloxy)ethoxy)ethoxy)ethoxy)-1,4- phenylene)diboronic acid with each of the diiodo-substituted BODIPY and Aza-BODIPY. Synthesized polymers exhibited high solubility even in polar solvents such as acetic acid. Their electronic and optical properties were studied by cyclic voltammetry, UV-vis absorption, and photoluminescence spectroscopies. The absorption and photoluminescence spectra of the obtained polymers were red-shifted in comparison with the corresponding monomers due to the increase in the HOMO level by the formation of donor-acceptor interactions and the expansion of main-chain conjugations, explained by their cyclic voltammograms and theoretical calculations of the model compounds using the density-functional theory method. Finally, the electron mobilities of the polymers were determined from the space-charge-limited current with electron-only device structure of ITO/Ca/polymer/BCP/LiF/Al. As a result, owing to their high electron acceptability and strong stacking interaction among the BODIPY or Aza-BODIPY units, it was found that the mobilities for the polymers ((1.5-3.6) × 10-4 [cm2 V-1 s -1]) were much higher than the value of Alq3 (5.8 × 10-5 [cm2 V-1 s-1]), and their threshold voltages (5-7 V) were much smaller than that of the Alq3 device (12 V). © 2014 American Chemical Society.


Miyazaki T.,Ehime University | Sumii R.,Institutes for Molecular Science | Sumii R.,Nagoya University | Umemoto H.,Nagoya University | And 7 more authors.
Chemical Physics | Year: 2012

Ultraviolet photoelectron spectra (UPS) and X-ray photoelectron spectra (XPS) of two erbium atoms and an erbium-carbide cluster entrapped fullerenes, Er 2@C 82 (I), Er 2@C 82 (III), Er 2C 2@C 82 (I) and Er 2C 2@C 82 (III), were measured using a synchrotron radiation light source and MgKα X-ray gun. The spectral onset energy of these endohedral fullerenes is around 0.8-0.9 eV, which is larger than that of Er@C 82 (I) of 0.4 eV. The UPS of erbium atoms encapsulated endohedral fullerenes having the same C 82 cage structure were analogous while those of the different cage structure are different. This finding supports an empirical rule that the electronic structure of the endohedral fullerenes is principally governed by the C 82 cage structure. The XPS Er4d 5/2 peak of Er 2@C 82 suggests the oxidation state of (Er 3+) 2 @C826-. The difference spectrum between the UPS of Er 2@C 82 (III) and Er 2C 2@C 82 (III) has the same C 3v structure reveals two excess electrons on the cage of Er 2@C 82. © 2011 Elsevier B.V. All rights reserved.


Miyazaki T.,Ehime University | Okita S.,Ehime University | Ohta T.,Ehime University | Yagi H.,Ehime University | And 6 more authors.
Chemical Physics | Year: 2015

Ultraviolet photoelectron spectra (UPS) of C80-Ih cage endohedral fullerenes, La2@C80 and Ce2@C80 were measured using a synchrotron radiation light source. The spectral onset energy of La2@C80 and Ce2@C80 is around 0.8-0.9 eV, which is smaller than that of empty C80-Ih. The UPS of these endohedral fullerenes are almost identical and are discussed with an aid of density functional theory (DFT) calculation. Simulation spectra calculated with using the results of the DFT calculations on an optimized structure starting from D3d geometry reproduces the UPS of La2@C80 and Ce2@C80 very well, which supports the theoretically proposed structure. © 2014 Elsevier B.V. All rights reserved.


Miyazaki T.,Ehime University | Tokumoto Y.,Ehime University | Sumii R.,Institutes for Molecular Science | Sumii R.,Nagoya University | And 4 more authors.
Chemical Physics | Year: 2014

Ultraviolet photoelectron spectra (UPS) and X-ray photoelectron spectra (XPS) of two thulium atoms and thulium-carbide cluster entrapped fullerenes, Tm2@C82 (III) and Tm2C2@C 82 (III), were measured using synchrotron radiation and MgKα X-ray light sources. The UPS spectral onset energy of these endohedral fullerenes is around 0.9 eV, which is smaller than that of 1.2 eV of empty C82. The UPS of Tm2@C82 (III) and Tm 2C2@C82 (III) resemble each other. Further, the UPS of Tm2@C82 (III), Y2@C82-C 3v and Er2@C82-C3 v are almost identical and as well as are Tm2C 2@C82 (III), Y2C2@C 82-C3v and Er2C2@C 82-C3v. The XPS Tm4d5/2 peaks of Tm2@C82 and Tm2C2@C82 appear at higher binding energy region than that of Tm@C82, which suggests the oxidation states of Tm atoms in Tm2@C82 (III) and Tm2C2@C82 are higher than that in Tm@C82. © 2014 Elsevier B.V. All rights reserved.


Yoshii R.,Kyoto University | Nagai A.,Institutes for Molecular Science | Tanaka K.,Kyoto University | Chujo Y.,Kyoto University
Journal of Polymer Science, Part A: Polymer Chemistry | Year: 2013

It is challenging to realize the near-infrared (NIR) emission with large brightness and sharp spectra from the conjugated polymers. In this study, we demonstrate the strategy for receiving strong and pure NIR emission from polymeric materials using organoboron complexes and the modification after polymerization. A series of NIR emissive conjugated polymers with boron di(iso)indomethenes (BODINs) and fluorene or bithiophene were synthesized by Suzuki-Miyaura coupling reaction. The obtained polymers exhibited high emissions in the range from deep-red to NIR region (quantum yields: φPL = 0.40-0.79, full width at half maximum height: Δλ1/2 = 660-940 cm-1, emission maxima: λPL = 686-714 nm). Next, the demethylation of the BODIN-based polymer with o-methoxyphenyl groups was carried out. The transformation of the polymer structure quantitatively proceeded via efficient intramolecular crosslinking through the intermediary of the boron atom. Finally, the resulting polymer showed both drastically larger red-shifted and sharper photoluminescence spectrum than that of the parent polymer with deep-red emission (φPL = 0.37, Δλ 1/2 = 460 cm-1, λPL = 758 nm). © 2013 Wiley Periodicals, Inc.


Tanaka K.,Kyoto University | Tamashima K.,Kyoto University | Nagai A.,Institutes for Molecular Science | Okawa T.,Osaka Gas Co. | Chujo Y.,Kyoto University
Macromolecules | Year: 2013

We present the facile modulation of the optical properties of the conjugated polymers via polymer reactions. The polymers composed of diketonate and fluorene were prepared, and boron complexation was performed after polymer synthesis. By changing feed ratios of BF3·Et2O, which is a reagent to produce a boron diketonate complex, the series of polymers with various complexation ratios with boron at the diketonate unit can be obtained. These synthesized polymers showed diverse optical properties. In the solution states, the quantum yields of emission were greatly changed by the complexation ratios with boron. Accordingly, the polymers with complexation ratio of 21% present the largest intensity. In addition, the emission color can be tuned by changing the complexation ratios in the films. From blue to orange, the emissions were achieved. It was revealed that induced charge transfer between fluorene and boron diketonate should be the main path for the emission of the synthesized polymers. © 2013 American Chemical Society.


Miyazaki T.,Ehime University | Sumii R.,Institutes for Molecular Science | Sumii R.,Nagoya University | Umemoto H.,Nagoya University | And 5 more authors.
Chemical Physics | Year: 2010

Ultraviolet photoelectron spectra (UPS) of Erbium endohedral fullerene Er@C82 (I) were measured using a synchrotron radiation light source. The spectral onset of Er@C82 (I) was 0.4 eV, which is smaller than those of divalent atom endohedral metallofullerenes and analogous to those of trivalent atom endohedral metallofullerenes. The upper valence structure (E b < 5 eV) of Er@C82 (I) was almost identical with those of C2v-Tb@C82 and C2v-La@C82. The oxidation states of Er in Er@C82 from the analogy of the oxidation state of Tb in Tb@C82 and La in La@C82 is estimated to be +3. The UPS of Er@C82 (I) differs from those of Tm@C82 isomers. The reason of the difference is attributed to differences in their cage structures and oxidation states. The upper valence UPS of Er@C82 (I) could be well reproduced by a simulated spectrum obtained with a Gaussian03 program module assuming C82-C2v cage structure with three additional electrons. © 2010 Elsevier B.V. All rights reserved.


Yoshii R.,Kyoto University | Nagai A.,Institutes for Molecular Science | Tanaka K.,Kyoto University | Chujo Y.,Kyoto University
Chemistry - A European Journal | Year: 2013

A series of boron ketoiminate derivatives that exhibited clear aggregation-induced emission (AIE) characteristics (in THF: Φ PL≤0.01; in the solid state: ΦPL=0.30-0.76) were prepared by the reactions of 1,3-enaminoketone derivatives with boron trifluoride-diethyl etherate. The structures and optical properties were investigated by UV-visible spectroscopy, photoluminescent (PL) spectroscopy, and X-ray single-crystal measurements. These results indicate that the AIE characteristics were derived from molecular motions of the boron-chelating rings with a boron-nitrogen (B-N) bond. Furthermore, the optical properties were controllable by steric hindrance of the substituted groups on the nitrogen atom. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Yoshii R.,Kyoto University | Nagai A.,Institutes for Molecular Science | Tanaka K.,Kyoto University | Chujo Y.,Kyoto University
Macromolecular Rapid Communications | Year: 2014

In this research, the synthesis of boron-ketoiminate-containing polymers is reported with large molecular weights (M̄n = 20 000) and their optical properties are examined by UV-vis absorption and photoluminescence spectrometries. It is shown that the polymers exhibit strong emission both in the solution and solid states (Φ PL,THF = 0.46-0.80, Φ PL,film = 0.13-0.38). These optical properties can be explained by a donor-acceptor interaction between the boron ketoiminate and the electron-donating comonomer such as fluorene or bithiophene. Furthermore, in the solid states, their emission colors can be successfully tuned from blue to orange by the substituents on the nitrogen atom with the difference of the steric hindrance (λ PL,THF = 464-546 nm, λ PL,film = 486-604 nm). © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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