Control of electron transfer pathways in a dye-sensitized solar cell

Using shaped laser pulses, we increase the yield of ultrafast electron injection from the sensitizer to TiO2 nanocrystals in the core part of a dye-sensitized solar cell. The temporal structure of the optimized excitation pulse is in clear correlation with nuclear oscillations in the impulsively excited dye molecule. From DFT structure optimization and normal mode analyses we identified the modes which are responsible for the oscillations. The best pulse shape suggests Impulsive Stimulated (anti-Stokes) Raman scattering as a key process of optimization.     

Gaussian random fields,infinite dimensional Ornstein-Uhlenbeck processes,and symmetric Markov processes

A general treatment of infinite dimensional Ornstein-Uhlenbeck processes (OUPs) is presented. Emphasis is put on their connection with ordinary Gaussian random fields, and OUPs as symmetric Markov processes. We also discuss the relation to second quantisation and Gaussian Markov random fields.Supported in part by the Swedish Natural Science Research Council, NFR.     

Structure investigation of TiIV-BODOLates involved in the catalytic asymmetric reduction of ketones using catecholborane

The complexes formed by the reaction of [Ti(OiPr)(4)] and bicyclo-octanediols (BODOLs) 1 and 2 (1:1) are useful as chiral catalysts in asymmetric reductions and were investigated by (1)H NMR spectroscopy and computational methods. A consistent picture emerged of head-to-tail dimers being kept together via a Ti-O-Ti-O micro-oxo bridge similar to the Ti-tartrates but different from the corresponding Ti-BINOLates and Ti-TADDOLates.     

Improved method for the synthesis of 2-alkylamino-2-deoxy-d-glucopyranose and 1,2-dialkylamino-1,2-dideoxy-d-(N)-beta-glucoside

An improved method for the synthesis of two types of carbohydrate-based, pH-sensitive surfactants has been developed. The surfactants are formed in almost quantitative yields from d-fructose and suitable alkylamines, when using a zinc halide salt as catalyst. The reaction proceeds via an initial Amadori reaction, and the 1,2-dialkylamino-1,2-dideoxy-d-(N)-beta-glucoside precipitates out of the reaction. The product can easily be hydrolyzed to the more water-soluble, surface-active, and pH-sensitive monoalkyl derivative 2-alkylamino-2-deoxy-d-glucopyranose. Products from several amines can be prepared.     

An improved synthesis of 3-[3-(trifluoromethyl)-3H-1,2-diazirin-3-yl]aniline: A key intermediate in the synthesis of photoaffinity probes

An improved synthesis of 3-[3-(trifluoromethyl)-3H-1,2-diazirin-3-yl]aniline, achieving an overall yield of 38% over seven steps is reported. Only three chromatographic separations were needed and the preparation of ～0.7 g of the target compound was demonstrated. The stability of the diazirine in solution at room temperature while exposed to ambient light was studied. No significant degradation of the compound was observed over the course of five weeks in a 130 mM sample and only minor degradation was observed in weaker samples (10, 5, and 2.5 mM), as demonstrated by ¹H and ¹⁹F NMR.     

Geminate charge recombination in alternating polyfluorene copolymer/fullerene blends

By measuring excited state and charge dynamics in blends of an alternating polyfluorene copolymer and fullerene derivative over nine orders in time and two orders in light intensity, we have monitored the light-induced processes from ultrafast charge photogeneration to much slower decay of charges by recombination. We find that at low light intensities relevant to solar cell operation relatively fast (approximately 30 ns) geminate recombination is the dominating charge decay process, while nongeminate recombination has a negligible contribution. The conclusion of our work is that under solar illumination conditions geminate recombination of charges may be directly competing with efficient charge collection in polymer/fullerene solar cells.     

Interactions between charged surfaces immersed in a polyelectrolyte solution

With grand canonical simulations invoking a configurationally weighted scheme, we have calculated interactions between charged surfaces immersed in a polyelectrolyte solution. In contrast to previous simulations of such systems, we have imposed full equilibrium conditions (i.e., we have included diffusive equilibrium with a bulk solution). This has a profound impact on the resulting interactions: even at modest surface charge densities, oppositely charged chains will, at sufficiently large separations, adsorb strongly enough to overcompensate for the nominal surface charge. This phenomenon, known as charge inversion, generates a double-layer repulsion and a free-energy barrier. Simpler canonical approaches, where the chains are assumed to neutralize the surfaces perfectly, will not capture this stabilizing barrier. The barrier height increases with the length of the polyions. Interestingly enough, the separation at which the repulsion becomes attractive is independent of chain length. The short chains here are unable to reach across from one surface to the other. We therefore conclude that the transition to an attractive regime is not provided by the formation of such "intersurface" bridges. With long chains and at large separations, charge inversion displays decaying oscillatory behavior (i.e., the apparent surface charge switches sign once again). This is due to polyion packing effects. We have also investigated responses to salt addition and changes in polyelectrolyte concentration. Our results are in qualitative and semiquantitative agreement with experimental findings, although it should be noted that our chains are comparatively short, and the experimental surface charge density is poorly established.     

Zur Kenntnis der Optik weißer Sole. I. Theoretische Ableitung des Absorptionskoeffizienten

Zusammenfassung Ausgehend von der mit gutem Resultate an anderen Kolloiden geprüften Mie'schen Theorie, werden die Absorptionskoeffizienten für wei?e Sole für verschiedene Brechungsindizes, Wellenl?ngen des einfallenden Lichtes und Teilchendurchmesser berechnet. Die theoretische Voraussetzung für methodisch einfache Messung der Konzentration, des Dispersit?tsgrades und eventuell auch der Polydispersit?t werden diskutiert und scheinen gro?e Aussichten zu praktischer Verwertung zu haben. Die Voraussetzungen der Absorbometrie für die quantitative Analyse dürften gro? sein. Eine genaue experimentelle Nachprüfung der in der Theorie gewonnenen Resultate ist erforderlich. Mit Rücksicht auf die zeitraubenden Berechnungen direkt aus der Theorie sind Kurven und Tabellen so aufgestellt, da? sie unter gewissen Voraussetzungen eine Berechnung des Absorptionskoeffizienten für ein beliebiges Sol gestatten.