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941.
Wangdong Zeng Dr. Masatoshi Ishida Sangsu Lee Young Mo Sung Dr. Zebing Zeng Yong Ni Prof. Chunyan Chi Prof. Dongho Kim Prof. Jishan Wu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(49):16814-16824
A p‐quinodimethane (p‐QDM)‐bridged porphyrin dimer 1 has been prepared for the first time. An unexpected Michael addition reaction took place when we attempted to synthesize compound 1 by reaction of the cross‐conjugated keto‐linked porphyrin dimers 8 a and 8 b with alkynyl/aryl Grignard reagents. Alternatively, compound 1 could be successfully prepared by intramolecular Friedel–Crafts alkylation of the diol‐linked porphyrin dimer 14 with concomitant oxidation in air. Compound 1 shows intense one‐photon absorption (OPA, λmax=955 nm, ε=45400 M ?1 cm?1) and a large two‐photon absorption (TPA) cross‐section (σ(2)max=2080 GM at 1800 nm) in the near‐infrared (NIR) region due to its extended π‐conjugation and quinoidal character. It also exhibits a short singlet excited‐state lifetime of 25 ps. The cyclic voltammogram of 1 displays multiple redox waves with a small electrochemical energy gap of 0.86 eV. The ground‐state geometry, electronic structure, and optical properties of 1 have been further studied by density functional theory (DFT) calculations and compared with those of the keto‐linked dimer 8 b . This research has revealed that incorporation of a p‐QDM unit into the porphyrin framework had a significant impact on its optical and electronic properties, leading to a novel NIR OPA and TPA chromophore. 相似文献
942.
Soaram Kim Hyunggil Park Giwoong Nam Hyunsik Yoon Jae-Young Leem 《Journal of Sol-Gel Science and Technology》2013,67(3):580-591
Sol–gel spin-coating was used to grow zinc oxide (ZnO) thin films doped with 0–2.5 at.% B on quartz substrates. The structural, optical, and electrical properties of the thin films were investigated using field-emission scanning electron microscopy, X-ray diffraction (XRD), photoluminescence (PL), ultraviolet–visible spectroscopy, and van der Pauw Hall-effect measurements. All the thin films had deposited well onto the quartz substrates and exhibited granular morphology. The average crystallite size, lattice constants, residual stress, and lengths of the bonds in the crystal lattice of the thin films were calculated from the XRD data. The PL spectra showed near-band-edge (NBE) and deep-level emissions, and B doping varied the PL properties and increased the efficiency of the NBE emission. The optical transmittance spectra for the undoped ZnO and boron-doped zinc oxide (BZO) thin films show that the optical transmittance of the BZO thin films was significantly higher than that of the undoped ZnO thin films in the visible region of the spectra and that the absorption edge of the BZO thin films was blue-shifted. In addition, doping the ZnO thin films with B significantly varied the absorption coefficient, optical band gap, Urbach energy, refractive index, extinction coefficient, single-oscillator energy, dispersion energy, average oscillator strength, average oscillator wavelength, dielectric constant, and optical conductivity of the BZO thin films. The Hall-effect data suggested that B doping also improved the electrical properties such as the carrier concentration, mobility, and resistivity of the thin films. 相似文献
943.
Hyun Ook Seo Dae Han Kim Kwang-Dae Kim Eun Ji Park Chae Won Sim Young Dok Kim 《Adsorption》2013,19(6):1181-1187
Adsorption and desorption of toluene on bare and TiO2-coated silica with a mean pore size of 15 nm under dry and humid conditions were studied using toluene breakthrough curves and temperature programmed desorption (TPD) of toluene and CO2. Two TiO2/silica samples (either partially or fully covered with TiO2) were prepared with 50 and 200 cycles of TiO2 atomic layer deposition (ALD), respectively. The capacity of silica to adsorb toluene improved significantly with TiO2-thin film coating under dry conditions. However, toluene desorption from the surface due to displacement by water was more pronounced for TiO2-coated samples than bare samples under humid conditions. In TPD experiments, silica with a thinner TiO2 film (50-ALD cycled) had the highest reactivity for toluene oxidation to CO2 both in the absence and presence of water. Toluene adsorption and oxidation reactivity of silica can be controlled by modifying the silica surface with small amount of TiO2 using ALD. 相似文献
944.
Hui‐Jun Yun Yun‐Ji Lee Seung‐Jin Yoo Prof. Dae Sung Chung Prof. Yun‐Hi Kim Prof. Soon‐Ki Kwon 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(39):13242-13248
We describe herein the synthesis of novel donor–acceptor conjugated polymers with dithienobenzodithiophenes (DTBDT) as the electron donor and 2,1,3‐benzothiadiazole as the electron acceptor for high‐performance organic photovoltaics (OPVs). We studied the effects of strategically inserting thiophene into the DTBDT as a substituent on the skeletal structure on the opto‐electronic performances of fabricated devices. From UV/Vis absorption, electrochemical, and field‐effect transistor analyses, we found that the thiophene‐containing DTBDT derivative can substantially increase the orbital overlap area between adjacent conjugated chains and thus dramatically enhance charge‐carrier mobility up to 0.55 cm2 V?1 s?1. The outstanding charge‐transport characteristics of this polymer allowed the realization of high‐performance organic solar cells with a power conversion efficiency (PCE) of 5.1 %. Detailed studies on the morphological factors that enable the maximum PCE of the polymer solar cells are discussed along with a hole/electron mobility analysis based on the space‐charge‐limited current model. 相似文献
945.
Prof. Mengtao Sun Dr. Zhenglong Zhang Prof. Zee Hwan Kim Prof. Hairong Zheng Prof. Hongxing Xu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(44):14958-14962
Heterogeneous catalysts play an important role in surface catalytic reactions, but selective bond breaking and control of reaction products in catalytic processes remain significant challenges. High‐vacuum tip‐enhanced Raman spectroscopy (HV‐TERS) is one of the best candidates to realize surface catalytic reactions. Herein, HV‐TERS was employed in a new method to control dissociation by using hot electrons, generated from plasmon decay, as plasmonic scissors. In this method, the N?N bond in 4,4′‐dimercaptoazobenzene was selectively dissociated by plasmonic scissors, and the reaction products formed from the radical fragment (SC6H5N) were controlled by varying the pH value. Under acidic conditions, p‐aminothiophenol was produced from the radical fragment by attachment of hydrogen ions, whereas under alkaline conditions, 4‐nitrobenzenethiol was obtained by attachment of oxygen ions to the substrate. 相似文献
946.
947.
Christopher M. Lee Ashutosh Mittal Anna L. Barnette Kabindra Kafle Yong Bum Park Heenae Shin David K. Johnson Sunkyu Park Seong H. Kim 《Cellulose (London, England)》2013,20(3):991-1000
Sum-frequency-generation (SFG) vibration spectroscopy is a technique only sensitive to functional groups arranged without centrosymmetry. For crystalline cellulose, SFG can detect the C6H2 and intra-chain hydrogen-bonded OH groups in the crystal. The geometries of these groups are sensitive to the hydrogen bonding network that stabilizes each cellulose polymorph. Therefore, SFG can distinguish cellulose polymorphs (Iβ, II, IIII and IIIII) which have different conformations of the exocyclic hydroxymethylene group or directionalities of glucan chains. The C6H2 asymmetric stretching peaks at 2,944 cm?1 for cellulose Iβ and 2,960 cm?1 for cellulose II, IIII and IIIII corresponds to the trans-gauche (tg) and gauche-trans (gt) conformation, respectively. The SFG intensity of the stretch peak of intra-chain hydrogen-bonded O–H group implies that the chain arrangement in cellulose crystal is parallel in Iβ and IIII, and antiparallel in II and IIIII. 相似文献
948.
Xiaobo Su Satoshi Kimura Masahisa Wada Ung-Jin Kim Shigenori Kuga 《Cellulose (London, England)》2013,20(3):1023-1029
Adsorption–complexation of cellulose by hydrazine solutions in water and toluene was studied for native cellulose of varied crystallinity. Penetration of hydrazine into cellulose takes place more readily in hydrazine solution of higher concentration and with cellulose of lower crystallinity, but the equilibrium uptake was nearly independent of crystallinity. Complexation from toluene solution takes place at lower hydrazine concentration in toluene than in water, presumably because of the difference in hydrazine–solvent interaction. The adsorption isotherm of hydrazine in water is likely to be sigmoid, implying a cooperative sorption mechanism. It can presumably be ascribed to the disordered structure in the course of complexation. 相似文献
949.
Mazhar Ul-Islam Waleed Ahmad Khattak Minkyung Kang Sang Min Kim Taous Khan Joong Kon Park 《Cellulose (London, England)》2013,20(1):253-263
Physicochemical properties of materials can be amended by altering their physical structure through different processing conditions. The present study was conducted to investigate the post-synthesis structural variations and physico-mechanical properties of bacterial cellulose (BC) sheets prepared using different drying methods. Wet BC sheets of the same origin were freeze dried (BC-FD), dried at room temperature (25 °C) (BC-DRT), and dried at elevated temperature (50 °C) (BC-DHT). FE-SEM micrographs revealed that BC-DRT and BC-DHT had a more tightly packed and compact structure than the loosely held fibrils of BC-FD. XRD analysis revealed the relative crystallinity of the BC sample to be 64.60, 59.16, and 47.20 % for BC-DHT, BC-DRT and BC-FD, respectively. The water holding capacity (WHC) of the BC-FD was higher than that of the other two samples. Four consecutive drying and rewetting cycles demonstrated that the WHC of all samples decreased with each cycle. The WHC of BC-DRT and BC-DHT was reduced to almost 0 after the first drying cycle, but the BC-FD samples were able to regain some of their WHC. The tensile strength and elongation modulus were in the order of BC-DHT > BC-DRT > BC-FD. Overall, the results of this study revealed that the post-synthetic processing conditions had a strong effect on the structure and physico-mechanical properties of BC. 相似文献
950.
We consider both divergence and non-divergence parabolic equations on a half space in weighted Sobolev spaces. All the leading coefficients are assumed to be only measurable in the time and one spatial variable except one coefficient, which is assumed to be only measurable either in the time or the spatial variable. As functions of the other variables the coefficients have small bounded mean oscillation (BMO) semi-norms. The lower-order coefficients are allowed to blow up near the boundary with a certain optimal growth condition. As a corollary, we also obtain the corresponding results for elliptic equations. 相似文献