摘要:

AbstractSome fundamental aspects of basic principles and applications of electroluminescence, based on organic low molecular weight compounds and polymeric compounds will be presented. The basic working principles and the basic construction of electroluminescent devices are described. Some factors affecting the efficiencies and lifetime or organic electroluminescent devices are reviewed, describing recent developments in dye‐based organic hetero‐junction and polymer systems. The distinctive advantages of these organic LEDs are high efficiency of all colors and potential ease of fabrication, offering the possibility of applications in flat‐panel displays. No attempt is made in the present article to review the whole field, but instead this interesting field is described by focusing on a few selected topics, and by describing few representative re

ISSN:0005-9021    

DOI:10.1002/bbpc.19961001002

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractDegenerate four wave mixing (DFWM) and laser induced thermal grating spectroscopy (LITGS) have been used to detect ethylene and methanol in mixtures with nitrogen, argon or helium in the pressure range between 0.005 and 18 bar. The grating forming step for both techniques was accomplished via absorption of radiation in the interference region from two beams from a single longitudinal mode CO2laser. For DFWM the same CO2laser and for LITGS a diode pumped Nd: YAG laser were employed to read out the transient grating. Using photo thermal deflection spectroscopy (PDS) as an independent spectroscopic method thermal effects were confirmed for total pressures above 0.1 bar. For both DFWM and LITGS signal intensities increased with buffer gas pressure due to collision induced transfer of optical excitation energy into translational degrees of freedom. The temporal behaviour of the IR‐grating generation and thermalization processes and the advantages of hydrocarbon trace species detection from thermal gratings at high pressures is discusse

ISSN:0005-9021    

DOI:10.1002/bbpc.19961001003

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractIt is possible to disturb the equilibrium velocity distribution of molecules in a gas by absorption of narrow band laser light. This leads to light induced transport phenomena. We report on experiments, where we have measured the pressure difference caused by light induced viscous flow and where we have separated the two nuclear spin modifications of CH3F with the help of light induced drift.

ISSN:0005-9021    

DOI:10.1002/bbpc.19961001004

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractThe prepolarisation potential influences the two‐dimensional nucleation kinetics of adsorbed neutral molecules on a mercury electrode in the system 5‐bromocytosine/Na2SO4. It was shown that for prepolarisation potentials located near the phase transition potential a significant amount of large clusters is formed, which after the jump into the condensation region become overcritical nuclei with an athermal distribution. Significant differences exist in the kinetics at the cathodic and the anodic edge of the condensation region, respectively. This indicates that the potential dependence of the adsorption isotherm of the neutral molecules can not be symmetrical, as supported usually. These investigations show furthermore that the nucleation rate is not solely a function of the applied potential, but depends also on the prepolarisation conditi

ISSN:0005-9021    

DOI:10.1002/bbpc.19961001005

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractCation radical salts of 3,3′,5,5′‐tetramethylbenzidine (TMB) were studied in terms of dimerization of the radical cation, and compared with the salts of other aromatic diamines, including Wurster's blue perchlorate. ESR spectra of several TMB salts were measured in solid‐state, and analyzed by the singlet‐triplet model for a radical dimer. The singlet‐triplet energy separation has been obtained as 0.15 eV for (TMB)ClO4. The dimerization of the TMB radical cation in acetonitrile solution of (TMB)ClO4was estimated from ESR and visible spectral results. In consequence, (TMB)+.is highly dimerizable in solution, compared with the systems of oth

ISSN:0005-9021    

DOI:10.1002/bbpc.19961001006

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractThe results of a differential anomalous X‐ray scattering (DAS) study on lead(II)acetate trihydrate, dissolved in 2‐methoxyethanol, are reported. Anomalous X‐ray scattering at two energies below the L3‐edge of lead (Pb) was used to determine the local environment of Pb and to get more precise information on the complex molecular structure of the liquid. The differential scattering intensities and their Fourier transform, the differential atom pair correlation function (DACPF), were obtained after an intricate data evolution procedure. The analysis of the DACPF provides strong evidence for a dimeric structure of lead(II)acetate trihydrate in the methoxyethanolic solution via lead ‐ oxygen ‐ lead

ISSN:0005-9021    

DOI:10.1002/bbpc.19961001007

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractUsing the pressure‐jump relaxation technique in combination with synchrotron X‐ray diffraction we have investigated the rate and mechanism of phase transformations of mesophases of the lecithin/fatty acid mixtures dimyristoylphosphatidylcholine/myristic acid (DMPC/MA) and dipalmitoylphosphatidylcholine/palmitic acid (DPPC/PA) in the molar ratio 1:2. The investigations have been made as a function of the pressure‐jump amplitude and at two different levels of hydration, 50 and 75 wt% H2O. For the investigation of the structure of the lipid systems at elevated pressures as well as for the study of the kinetics of lipid phase transitions using the pressure‐jump technique, we built a high pressure X‐ray cell suitable for studies up to pressures of 2 kbar at temperatures ranging up to 140°C. In the first part of the paper, the temperature and pressure dependent structure and equilibrium phase behaviour of the two lecithin/fatty acid mixtures is discussed. In equilibrium, the chain melting transition of both mixtures occurs without forming a lamellar liquid‐crystalline Lαphase. In DMPC/MA (1:2) dispersions the phase sequence is L ccom/Lc→Lc→Lβ→HII/Q IIP/Q IID→HII, in DPPC/PA (1:2) L ccomL/Lc→Lβ→HIIwith increasing temperature or decreasing pressure, respectively. A temperature‐pressure phase diagram has been established in the temperature range from 0‐100°C at pressures from ambient up to 1500 bar for both systems. Pressure‐jumps within the inverted hexagonal/Q PIIcubic phase coexisting region of DMPC/MA (1:2) lead to a slight change of the composition of the mixture, and the structural relaxation process of the lattices proceeds in several steps. The rate‐determining part of the structural relaxation process is probably due to the restricted diffusion of water in and into the lattices and the relaxation of the hexagonal and cubic structures are found to be coupled to each other. Equilibrium values of the lattice constants are reached after about 30 s. Formation of further cubic lattices is possible, depending on the level of hydration. Experiments on the rate of the Lβ→HII/Q PIIchain melting transition of DMPC/MA (1:2) exhibit the occurence of a long‐lived intermediate Lαphase, which is not observed under equilibrium conditions. The HIIlattice starts to develop within the time‐resolution of this experiment, i.e. within the first 200 ms. First Bragg reflections of the cubic phase appear about 100 s after the pressure‐jump. Equilibrium values of the lattice constants are not reached before 30 min. The pressure‐jump amplitude has been found to have a significant influence on the kinetics of the phase transformation, the mechanism remaining. The increase of the pressure‐jump amplitude leads to a faster decay of the Lβphase and the more rapid formation of the HIIphase. The Lβ→HIItransition of DPPC/PA (1:2) dispersion follows a simpler kinetics. No intermediate Lαphase is found. The transition is complete about 25 s after a pressure‐jump from 520 to 200 bar at 71 °C, and it seems to be a simple

ISSN:0005-9021    

DOI:10.1002/bbpc.19961001008

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractMultivariational analyses were performed to separate the contribution of electronic and steric effects of alkyl groups on the experimental hydrocarbon acidities of four different sets of compounds, consisting of hydrocarbons (SET‐I), acetophenone derivatives (SET‐II), and acetone CH3COCHR1R2derivatives, where the acidity of the protons on the alkyl substituted site, (SET‐III), and the acidity of the methyl protons are both investigated (SET‐IV). Significant regression was obtained upon backward elimination for the first and last set. Due to the colinearity of the parameters in SETs‐II and ‐III the significance of the correlation is not so high. As expected, the gas phase acidity of the hydrocarbons in SET‐I is very sensitive to the polarizability and electronegativity of the alkyl substituents. The substituent have similar effects on the solution acidities of the ketone derivatives in SETs‐II, ‐III, though suppressed due to solvation, unlike the cases in SET‐II and SET‐III, the effects of the substituents in SET‐IV, where the substituents are relatively far away from the carbanion center generated are strongly reduced and reversed. This different behavior may be attributed to the domination of the solvent effects. Theoretical acidities of these compounds were calculated using the semiempirical methods such as MNDO, AM1 and PM3. The results are, quantitatively and qualitatively, unsatisfactory for the gas phase, as well as for the solution acidities. Multivariational analysis of substituent effects shows the insufficiency of the present parametrization to reflect the substituent effect properly. It seems that all these semiempirical methods are useless in prediction of carbon acidities, without reparametrization using carefully sel

ISSN:0005-9021    

DOI:10.1002/bbpc.19961001009

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractAn amphiphilic porphyrin derivative, 4,4′,4″,4‴‐(21 H,23 H‐porphine‐5,10,15,20‐tetrayl)tetrakis[1‐hexadecyl‐pyridinium] cation or its zinc complex (abbreviated as MC16TPyP), was preferentially impregnated on a single surface of an ultrathin poly(vinylchloride) film prepared by casting the polymer solution on water. Enrichment of the cationic porphyrin moiety to the polymer‐water interface during the film preparation was strongly indicated by contact‐angle measurement of water‐droplets on the dry surface. A subsequent treatment of the film with an aqueous solution, which contained an anionic porphyrin (4,4′,4″,4‴‐(21 H, 23 H‐porphine‐5,10,15,20‐tetrayl)tetrakis[p‐benzenesulfonate]anion or its copper or zinc complex: MTPPS), led to molecular association of the two‐types of porphyrins (MC16TPyP‐M'TPPS) on the film surface. Spectroscopic evidences for the formation of molecular association on the thin film were obtained by measuring electronic absorption, fluoresce

ISSN:0005-9021    

DOI:10.1002/bbpc.19961001010

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractFor several Ga defect chalcopyrites and one In spinel we determined nuclear quadrupole coupling constants and electric field gradients (EFG) from NMR measurements of the second order shift of the69Ga and115In resonances. A model is proposed for the lattice contribution and the orbital contribution of the EFG.

ISSN:0005-9021    

DOI:10.1002/bbpc.19961001011

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY