Organometallic complexes as hole-transporting materials in organic light-emitting diodes

The use of metal complexes fac-tris(1-phenylpyrazolato-N,C(2)('))cobalt(III) [fac-Co(ppz)(3)], fac-tris(2-phenylpyridinato-N,C(2)(') cobalt(III) [fac-Co(ppy)(3)], and [tris[2-((pyrrole-2-ylmethylidene)amino)ethyl]amine]gallium(III) [Ga(pma)] as materials for hole-transporting layers (HTL) in organic light-emitting diodes (OLEDs) is reported. Co(ppz)(3) and Co(ppy)(3) were prepared by following literature procedures and isolated as mixtures of facial (fac) and meridional (mer) isomers. The more stable fac isomers were separated from the unstable mer forms via column chromatography and thermal gradient sublimation. Crystals of fac-Co(ppz)(3) are monoclinic, space group P2(1)/c, with a = 13.6121(12) A, b = 15.5600(12) A, c = 22.9603(17) A, beta = 100.5 degrees, V = 4781.3(7) A(3), and Z = 8. [Tris[2-((pyrrol-2-ylmethylidene)amino)ethyl]amine]gallium [Ga(pma)] was prepared by the reaction of gallium(III) nitrate with the pmaH(3) ligand precursor in methanol. Ga(pma) crystallizes in the cubic space group I3d with cell parameters a = 20.2377(4) A, b = 20.2377(4) A, c = 20.2377(4) A, beta = 90.0 degrees, V = 8288.6(3) A(3), and Z = 16. These cobalt and gallium complexes are pale colored to colorless solids, with optical energy gaps ranging 2.6-3.36 eV. A two-layer HTL/ETL (ETL = electron-transporting layer) device structure using fac-Co(ppz)(3) and fac-Co(ppy)(3) as the HTL does not give efficient electroluminescence. However, the introduction of a thin layer of a hole-transporting material (N,N'-bis(1-naphthyl)-N,N'-diphenylbenzidine, NPD) as an energy "stair-step" and electron/exciton-blocker dramatically improves the device performance. Both fac-Co(ppz)(3) and fac-Co(ppy)(3) devices give external quantum efficiencies higher than 1.0%, with brightness 5000 and 7000 Cd/m(2) at 10 V, respectively. Ga(pma) also functions as an efficient interface layer, giving device performances very similar to those of analogous devices using NPD as the interface layer. Stability tests have been carried out for Co(ppz)(3)/NPD/Alq(3) and Co(ppy)(3)/NPD/Alq(3) devices. While fac-Co(ppy)(3) gave stable OLEDs, the fac-Co(ppz)(3)-based devices had very short lifetimes. On the basis of the experimental results of chemical oxidation of fac-Co(ppz)(3), the major cause for the fast decay of the fac-Co(ppz)(3) device is proposed to be the decomposition of fac-Co(ppz)(3)(+) in the HTL layer during the device operation.     

Haar wavelets of higher order on fractals and regularity of functions

Wavelets of Haar type of higher order m on self-similar fractals were introduced by the author in J. Fourier Anal. Appl. 4 (1998) 329-340. These are piecewise polynomials of degree m instead of piecewise constants. It was shown that for certain totally disconnected fractals, spaces of functions defined on the fractal may be characterized by means of the magnitude of the wavelet coefficients of the functions. In this paper, the study of these wavelets is continued. It is shown that also in the case when the fractals are not totally disconnected, the wavelets can be used to study regularity properties of functions. In particular, the self-similar sets considered can be, e.g., an interval in or a cube in . It turns out that it is natural to use Haar wavelets of higher order also in these classical cases, and many of the results in the paper are new also for these sets.     

Protein adsorption onto silica nanoparticles: conformational changes depend on the particles' curvature and the protein stability

We have analyzed the adsorption of protein to the surfaces of silica nanoparticles with diameters of 6, 9, and 15 nm. The effects upon adsorption on variants of human carbonic anhydrase with differing conformational stabilities have been monitored using methods that give complementary information, i.e., circular dichroism (CD), nuclear magnetic resonance (NMR), analytical ultracentrifugation (AUC), and gel permeation chromatography. Human carbonic anhydrase I (HCAI), which is the most stable of the protein variants, establishes a dynamic equilibrium between bound and unbound protein following mixture with silica particles. Gel permeation and AUC experiments indicate that the residence time of HCAI is on the order of approximately 10 min and slowly increases with time, which allows us to study the effects of the interaction with the solid surface on the protein structure in more detail than would be possible for a process with faster kinetics. The effects on the protein conformation from the interaction have been characterized using CD and NMR measurements. This study shows that differences in particle curvature strongly influence the amount of the protein's secondary structure that is perturbed. Particles with a longer diameter allow formation of larger particle-protein interaction surfaces and cause larger perturbations of the protein's secondary structure upon interaction. In contrast, the effects on the tertiary structure seem to be independent of the particles' curvature.     

Obtaining the bidirectional transmittance distribution function of isotropically scattering materials using an integrating sphere

This paper demonstrates a method to determine the bidirectional transmittance distribution function (BTDF) using an integrating sphere. Information about the sample’s angle-dependent scattering is obtained by making transmittance measurements with the sample at different distances from the integrating sphere. Knowledge about the illuminated area of the sample and the geometry of the sphere port in combination with the measured data combines to a system of equations that includes the angle-dependent transmittance.The resulting system of equations is an ill-posed problem which rarely gives a physical solution. A solvable system is obtained by using Tikhonov regularization on the ill-posed problem. The solution to this system can then be used to obtain the BTDF.Four bulk-scattering samples were characterised using two goniophotometers and the described method to verify the validity of the new method. The agreement shown is excellent for the more diffuse samples. The solution to the low-scattering samples contains unphysical oscillations, but still gives the correct shape of the solution. The origin of the oscillations and why they are more prominent in low-scattering samples are discussed.     

Synthesis of the dibenzo[f,h]phthalazine and dibenzo[f,h]cinnoline skeleton via a ‘Suzuki-Pd-catalyzed intramolecular arylation’ and a ‘Suzuki-Pschorr’ approach

Palladium-catalyzed intramolecular arylation of 2-benzyl-5-(2-bromophenyl)-4-phenylpyridazin-3(2H)-one yielded hitherto unknown 2-benzyldibenzo[f,h]phthalazin-1(2H)-one. The synthesis of this new tetracyclic pyridazinone from 2-benzyl-5-(2-aminophenyl)-4-phenylpyridazin-3(2H)-one via a Pschorr type reaction was also investigated. Similarly, the construction of 2-methyldibenzo[f,h]cinnolin-3(2H)-one from 2-methyl-5-(2-bromophenyl)-6-phenylpyridazin-3(2H)-one and 2-methyl-5-(2-aminophenyl)-6-phenylpyridazin-3(2H)-one is also reported. Removal of the N-benzyl protective group of 2-benzyl-dibenzo[f,h]phthalazin-1(2H)-one with AlCl₃ yielded unsubstituted dibenzo[f,h]phthalazin-1(2H)-one.     

Trace determination of volatile sulfur compounds by solid-phase microextraction and GC-MS

A method was developed for the simultaneous determination of the following nine volatile sulfur compounds in gas samples: carbon disulfide, carbonyl sulfide, ethyl sulfide, ethyl methyl sulfide, hydrogen sulfide, isopropanethiol, methanethiol, methyl disulfide and methyl sulfide. The target compounds were preconcentrated by solid-phase microextraction (SPME) and determined by gas chromatography combined with mass spectrometry. Experimental design was employed to optimize the extraction time and temperature and concurrent detection of the nine compounds was achieved by using an SPME fiber coated with Carboxen-polydimethylsiloxane (75 microns). Detection limits ranged from 1 ppt (v/v) for carbon disulfide to 350 ppt (v/v) for hydrogen sulfide and calibration functions were linear up to 20 ppb (v/v) for all the compounds investigated.     

Quantum magnetism in the paratacamite family: towards an ideal kagomé lattice

We report muon spin rotation measurements on the S=1/2 (Cu2+) paratacamite ZnxCu4-x(OH)6Cl2 family. Despite a Weiss temperature of approximately -300 K, the x=1 compound is found to have no transition to a magnetic frozen state down to 50 mK as theoretically expected for the kagomé Heisenberg antiferromagnet. We find that the limit between a dynamical and a partly frozen ground state occurs around x=0.5. For x=1, we discuss the relevance to a singlet picture.     

Selective oxidation of methane by the bis(mu-oxo)dicopper core stabilized on ZSM-5 and mordenite zeolites

This work reports on the capability of the O2-activated Cu-ZSM-5 and Cu-MOR zeolites to selectively convert methane into methanol at a temperature of 398 K. A strong correlation between (i) the activity and (ii) the intensity of the 22 700 cm-1 UV-vis band, assigned to the bis(mu-oxo)dicopper core, is found (i) as a function of the reaction temperature, (ii) as a function of the Cu loading of the zeolite, and (iii) in comparison to other Cu materials. These three lines of evidence firmly support the key role of the bis(mu-oxo)dicopper core in this selective, low-temperature hydroxylation of methane.     

Conversion of sodium lactate to lactic acid with water-splitting electrodialysis

The conversion of sodium lactate to lactic acid with water-splitting electrodialysis was investigated. One way of reducing the power consumption is to add a conductive layer to the acid compartment. Doing this reduced the power consumption by almost 50% in a two-compartment cell, whereas the electric current efficiency was not affected at all. Three different solutions were treated in the electrodialysis unit: a model solution with 70 g/L of sodium lactate and a fermentation broth that had been prefiltered two different ways. The fermentation broth was either filtered in an open ultrafiltration membrane (cut-off of 100,000 Dalton) in order to remove the microorganisms or first filtered in the open ultrafiltration membrane and then in an ultrafiltration membrane with a cut-off of 2000 Dalton to remove most of the proteins. The concentration of sodium lactate in the fermentation broth was 70 g/L, as well. Organic molecules present in the broth (peptides and similar organic material) fouled the membranes and, therefore, increased power consumption. Power consumption increased more when permeate from the more open ultrafiltration membrane was treated in the electrodialysis unit than when permeate from the membrane with the lower cut-off was treated, since there was a higher amount of foulants in the former permeate. However, the electrodialysis membranes could be cleaned efficiently with a 0.1 M sodium hydroxide solution.