In-plane oxygen diffusion measurements in polymer films using time-resolved imaging of programmable luminescent tags

Oxygen diffusion properties in thin polymer films are key parameters in industrial applications from food packaging, over medical encapsulation to organic semiconductor devices and have been continuously investigated in recent decades. The established methods have in common that they require complex pressure-sensitive setups or vacuum technology and usually do not come without surface effects. In contrast, this work provides a low-cost, precise and reliable method to determine the oxygen diffusion coefficient D in bulk polymer films based on tracking the phosphorescent pattern of a programmable luminescent tag over time. Our method exploits two-dimensional image analysis of oxygen-quenched organic room-temperature phosphors in a host polymer with high spatial accuracy. It avoids interface effects and accounts for the photoconsumption of oxygen. As a role model, the diffusion coefficients of polystyrene glasses with molecular weights between 13k and 350k g/mol are determined to be in the range of (0.8-1.5) × 10-7 cm2/s, which is in good agreement with previously reported values. We finally demonstrate the reduction of the oxygen diffusion coefficient in polystyrene by one quarter upon annealing above its glass transition temperature.

Experimental proof of Joule heating-induced switched-back regions in OLEDs

Organic light-emitting diodes (OLEDs) have become a major pixel technology in the display sector, with products spanning the entire range of current panel sizes. The ability to freely scale the active area to large and random surfaces paired with flexible substrates provides additional application scenarios for OLEDs in the general lighting, automotive, and signage sectors. These applications require higher brightness and, thus, current density operation compared to the specifications needed for general displays. As extended transparent electrodes pose a significant ohmic resistance, OLEDs suffering from Joule self-heating exhibit spatial inhomogeneities in electrical potential, current density, and hence luminance. In this article, we provide experimental proof of the theoretical prediction that OLEDs will display regions of decreasing luminance with increasing driving current. With a two-dimensional OLED model, we can conclude that these regions are switched back locally in voltage as well as current due to insufficient lateral thermal coupling. Experimentally, we demonstrate this effect in lab-scale devices and derive that it becomes more severe with increasing pixel size, which implies its significance for large-area, high-brightness use cases of OLEDs. Equally, these non-linear switching effects cannot be ignored with respect to the long-term operation and stability of OLEDs; in particular, they might be important for the understanding of sudden-death scenarios.

Highly Luminescent and Water-Resistant CsPbBr3-CsPb2Br5 Perovskite Nanocrystals Coordinated with Partially Hydrolyzed Poly(methyl methacrylate) and Polyethylenimine

All inorganic lead halide perovskite nanocrystals (PNCs) typically suffer from poor stability against moisture and UV radiation as well as degradation during thermal treatment. The stability of PNCs can be significantly enhanced through polymer encapsulation, often accompanied by a decrease of photoluminescence quantum yield (PLQY) due to the loss of highly dynamic oleylamine/oleic acid (OLA/OA) ligands. Herein, we propose a solution for this problem by utilizing partially hydrolyzed poly(methyl methacrylate) (h-PMMA) and highly branched poly(ethylenimine) (b-PEI) as double ligands stabilizing the PNCs already during the mechanochemical synthesis (grinding). The hydrophobic polymer of h-PMMA imparts excellent film-forming properties and water stability to the resulting NC-polymer composite. In its own turn, the b-PEI forms an amino-rich, strongly binding ligand layer on the surface of the PNCs being responsible for the significant improvement of the PLQY and the stability of the resulting material. Moreover, the introduction of b-PEI promotes a partial phase conversion from CsPbBr₃ to CsPb₂Br₅ to obtain CsPbBr₃/CsPb₂Br₅ nanocrystals with a core-shell-like structure. As-prepared PNCs solutions are directly processable as inks, while their PLQY drops only slightly from 75% in colloidal solution to 65% in films. Moreover, the final PNC-polymer film exhibits excellent stability against water, heat, and ultraviolet light irradiation. These superior properties allowed us to fabricate a proof of concept thin film OLED with h-PMMA/b-PEI-stabilized PNCs as an easily processable, narrowly emitting color conversion composite material.

Simultaneous Singlet-Singlet and Triplet-Singlet Förster Resonance Energy Transfer from a Single Donor Material

For almost 70 years, Förster resonance energy transfer (FRET) has been investigated, implemented into nowadays experimental nanoscience techniques, and considered in a manifold of optics, photonics, and optoelectronics applications. Here, we demonstrate for the first time simultaneous and efficient energy transfer from both donating singlet and triplet states of a single photoluminescent molecular species. Using a biluminescent donor that can emit with high yield from both excited states at room temperature allows application of the FRET framework to such a bimodal system. It serves as an exclusive model system where the spatial origin of energy transfer is exactly the same for both donating spin states involved. Of paramount significance are the facts that both transfers can easily be observed by eye and that Förster theory is successfully applied to state lifetimes spanning over 8 orders of magnitude.

A Silicon-Singlet Fission Tandem Solar Cell Exceeding 100% External Quantum Efficiency with High Spectral Stability

After 60 years of research, silicon solar cell efficiency saturated close to the theoretical limit, and radically new approaches are needed to further improve the efficiency. The use of tandem systems raises this theoretical power conversion efficiency limit from 34% to 45%. We present the advantageous spectral stability of using voltage-matched tandem solar cells with respect to their traditional series-connected counterparts and experimentally demonstrate how singlet fission can be used to produce simple voltage-matched tandems. Our singlet fission silicon-pentacene tandem solar cell shows efficient photocurrent addition. This allows the tandem system to benefit from carrier multiplication and to produce an external quantum efficiency exceeding 100% at the main absorption peak of pentacene.

[Echinococcosis with special reference to lung involvement]

In 31 patients with echinococciasis, the medical history, diagnostic and therapeutic aspects were evaluated. Six of these patients revealed an involvement of the lungs. Their symptoms--deteriorated general condition, pain in the chest, coughing or haemoptysis, were unspecific. Nineteen patients were submitted to surgery; ten patients received intermittent mebendazole. Treatment with this drug resulted in a stabilisation of the patient's condition. In inoperable patients, treatment with benzimidazolene should at least be attempted.

Comparative pharmacokinetics of intravenous ofloxacin and ciprofloxacin

In ten volunteers the pharmacokinetics of ofloxacin and ciprofloxacin were determined after crossover administration of 100 and 200 mg intravenously (30 min constant infusion). Concentrations in serum and urine were measured by HPLC. Concentrations in serum following parenteral ofloxacin dosages demonstrated dose dependency with long biological half-lives. Pharmacokinetic parameters were calculated on the basis of an open three-compartment model, which resulted in a high volume of distribution for both substances (166-246 1 for ofloxacin, 178-2611 for ciprofloxacin). AUC for ofloxacin was three times higher than that for ciprofloxacin. Approximately 80% of ofloxacin and 57% of ciprofloxacin were eliminated through the kidneys. Ciprofloxacin had a considerable amount of extrarenal clearance, whereas only 19% of ofloxacin were eliminated by extrarenal mechanisms. Only 4.3% of ofloxacin after iv dosing could be detected as metabolites in urine.

Pharmacokinetics of ofloxacin after parenteral and oral administration

In 10 volunteers, the pharmacokinetics of ofloxacin [HOE 280, DL 8280; (+/-)-9-fluoro-2,3-dihydro-3-methyl-10-(4-methyl-1-piperazinyl)-7-oxo-7H -pyrido-[1,2,3-de] [1,4]benzoxacine-6-carboxylic acid] was determined after administration of 25, 50, 100, and 200 mg intravenously (30-min infusion) as well as 200 and 400 mg orally. Concentrations in serum and urine were measured by high-pressure liquid chromatography. Concentrations in serum following different parenteral ofloxacin dosages demonstrated dose dependency with long biological half-lives of 231 to 267 min. Pharmacokinetic parameters were calculated on the basis of open two- and three-compartment models, which yielded nearly identical results. High volumes of distribution (1.2 to 1.4 liters/kg of body weight) suggested effective diffusion into the extravascular space. High total and renal clearances indicated primarily renal excretion with additional elimination pathways, such as tubular secretion and extrarenal elimination. After oral administration, absorption was excellent, and the absolute bioavailability following 200 mg of ofloxacin could be calculated at greater than 0.95. Maximal concentrations in serum were attained 1.2 to 1.9 h after dosing; areas under the curve increased in proportion to dose between 200 and 400 mg of oral ofloxacin. The amount of known metabolites (demethyl and N-oxide compounds) excreted in urine reached only 4.3% (intravenously) and 4.0% (orally). Transient headaches in some volunteers were the only side effects registered.