排序方式: 共有115条查询结果,搜索用时 0 毫秒
111.
Veldman D Ipek O Meskers SC Sweelssen J Koetse MM Veenstra SC Kroon JM van Bavel SS Loos J Janssen RA 《Journal of the American Chemical Society》2008,130(24):7721-7735
The electro-optical properties of thin films of electron donor-acceptor blends of a fluorene copolymer (PF10TBT) and a fullerene derivative (PCBM) were studied. Transmission electron microscopy shows that in these films nanocrystalline PCBM clusters are formed at high PCBM content. For all concentrations, a charge transfer (CT) transition is observed with absorption spectroscopy, photoluminescence, and electroluminescence. The CT emission is used as a probe to investigate the dissociation of CT excited states at the donor-acceptor interface in photovoltaic devices, as a function of an applied external electric field and PCBM concentration. We find that the maximum of the CT emission shifts to lower energy and decreases in intensity with higher PCBM content. We explain the red shift of the emission and the lowering of the open-circuit voltage (V(OC)) of photovoltaic devices prepared from these blends with the higher relative permittivity of PCBM (epsilon(r) = 4.0) compared to that of the polymer (epsilon(r) = 3.4), stabilizing the energy (E(CT)) of CT states and of the free charge carriers in blends with higher PCBM concentration. We show that the CT state has a short decay time (tau = ca. 4 ns) that is reduced by the application of an external electric field or with increasing PCBM content. The field-induced quenching can be explained quantitatively with the Onsager-Braun model for the dissociation of the CT states when including a high electron mobility in nanocrystalline PCBM clusters. Furthermore, photoinduced absorption spectroscopy shows that increasing the PCBM concentration reduces the yield of neutral triplet excitons forming via electron-hole recombination, and increases the lifetime of radical cations. The presence of nanocrystalline domains with high local carrier mobility of at least one of the two components in an organic heterojunction may explain efficient dissociation of CT states into free charge carriers. 相似文献
112.
3-Alkyl(aryl)-4-amino-4,5-dihydro-1H-1,2,4-triazol-5-ones 2a-g reacted with 4-diethylaminobenzaldehyde to afford the corresponding 3-alkyl(aryl)-4-(4-diethyl-aminobenzylidenamino)-4,5-dihydro-1H-1,2,4-triazol-5-ones 3a-g. The acetylation reactions of compounds 3a-e were investigated and compounds 4a-e were thus obtained. The new compounds were characterized using IR, (1)H-NMR, (13)C-NMR, UV and MS spectral data. In addition, the newly synthesized compounds 3a-g were titrated potentiometrically with tetrabutylammonium hydroxide in four non-aqueous solvents such as isopropyl alcohol, tert-butyl alcohol, acetone and N,N-dimethylformamide (DMF), and the half-neutralization potential values and the corresponding pKa values were determined for all cases. Moreover, 3 and 4 type compounds were also screened for their antioxidant activities. 相似文献
113.
Ozlem Celik Engin Tiras Sukru Ardali Sefer B. Lisesivdin Ekmel Ozbay 《Central European Journal of Physics》2012,10(2):485-491
The longitudinal optical (LO) phonon energy in AlGaN/GaN heterostructures is determined from temperature-dependent Hall effect
measurements and also from Infrared (IR) spectroscopy and Raman spectroscopy. The Hall effect measurements on AlGaN/GaN heterostructures
grown by MOCVD have been carried out as a function of temperature in the range 1.8-275 K at a fixed magnetic field. The IR
and Raman spectroscopy measurements have been carried out at room temperature. The experimental data for the temperature dependence
of the Hall mobility were compared with the calculated electron mobility. In the calculations of electron mobility, polar
optical phonon scattering, ionized impurity scattering, background impurity scattering, interface roughness, piezoelectric
scattering, acoustic phonon scattering and dislocation scattering were taken into account at all temperatures. The result
is that at low temperatures interface roughness scattering is the dominant scattering mechanism and at high temperatures polar
optical phonon scattering is dominant. 相似文献
114.
Acıkara OB Citoğlu GS Dall'acqua S Smejkal K Cvačka J Zemlička M 《Natural product research》2012,26(20):1892-1897
A novel triterpene 1 (3-β-hydroxy-fern-7-en-6-one-acetate) together with four known compounds, urs-12-en-11-one-3-acetyl (2), 3-β-hydroxy-fern-8-en-7-one-acetate (3), olean-12-en-11-one-3-acetyl (4) and leucodin (5) were obtained from the S. latifolia roots. All compounds were isolated from the n-hexane extract of S. latifolia roots using several chromatographic techniques. The structure of the isolated compounds was elucidated on the basis of (1)H-NMR, (13)C-NMR and 2D NMR data (HMBC, HMQC, COSY, TOCSY, NOESY, DEPT) as well as GC EITOF-HRMS. 相似文献
115.
Meryem Fistikci Ozlem Gundogdu Derya Aktas Hasan Secen M. Fethi Sahin Ramazan Altundas Yunus Kara 《Tetrahedron》2012,68(12):2607-2610
A new synthetic strategy for (R)- and (S)-3-hydroxy-4-(2,4,5-trifluorophenyl)butanoic acid, a building block in the preparation of sitagliptin and its derivatives, was developed. Pd(OAc)2 catalyzed coupling of 2,4,5-trifluoro-1-iodobenzene with allyl alcohol gave 3-(2,4,5-trifluorophenyl)propanal in a yield of 95%. l-Proline catalyzed reaction of the 3-phenylpropanal (in only 1.2 molar equiv) with nitrosobenzene followed by reduction with NaBH4 and Pd/C catalyzed hydrogenation gave (R)-3-(2,4,5-trifluorophenyl)propane-1,2-diol with >99% ee and 65% yield. Selective tosylation of primary hydroxyl group of the 1,2-propandiol unit followed by cyanide displacement afforded (R)-3-hydroxy-4-(2,4,5-trifluorophenyl)butanenitrile (80%). The nitrile was converted to the title β-hydroxy acid under basic hydrolysis in a yield of 90%. Thus, (R)-3-hydroxy-4-(2,4,5-trifluorophenyl)butanoic acid was prepared enantioselectively from the starting material in four steps and 45% overall yield. The reaction sequence was repeated with d-proline as the catalyst to give (S)-3-hydroxy-4-(2,4,5-trifluorophenyl)butanoic acid in 45% overall yield and >99% enantiomeric excess. 相似文献