Lorenz Walder

6-Peroxo-6-Zirconium Crown and Its Hafnium Analogue Embedded in a Triangular Polyanion: [M6(O2)6(OH)6(γ-SiW10O36)3]18− (M = Zr, Hf)

We have synthesized and structurally characterized the unprecedented peroxo-zirconium(IV) containing [Zr6(O2)6(OH)6(gamma-SiW10O36)3]18- (1). Polyanion 1 comprises a cyclic 6-peroxo-6-zirconium core stabilized by three decatungstosilicate units. We have also prepared the isostructural hafnium(IV) analogue [Hf6(O2)6(OH)6(gamma-SiW10O36)3]18- (2). We investigated the acid/base and redox properties of 1 by UV-vis spectroscopy and electrochemistry studies. Polyanion 1 represents the first structurally characterized Zr-peroxo POM with side-on, bridging peroxo units. The simple, one-pot synthesis of 1 and 2 involving dropwise addition of aqueous hydrogen peroxide could represent a general procedure for incorporating peroxo groups into a large variety of transition metal and lanthanide containing POMs.

Nanocrystalline electrochromic displays

Nanocrystalline electrochromic electrodes offer a promising outlook for the realization of displays characterized by sharp contrast and fast switching. These electrodes are constituted of sintered nanoparticles of a semiconductor, for instance titanium dioxide. Owing to the high porosity of the material, the signal produced by the color change associated to the oxidation or reduction of an adsorbed molecular monolayer can be amplified by a factor of 100‐1000, allowing transmittance changes from 79 to 11% of the complete electrode in less than 1 s.q 1999 Elsevier Science B.V. All rights reserved.

Photoinduced electron transfer and redox-type photochromism of a TiO2-anchored molecular diad

A linear, rigid molecular diad constituted of an electron donor (triarylamine, D) linked to a chromophore [Ru–bis(terpyridine), S] is synthesized; upon anchoring onto a nanocrystalline TiO2 electrodes this produces a charge-separated state D+–S |(e–) TiO2 under illumination decaying with k= 7 × 107 s–1(70%), 3 × 105 s–1(20%) and 4 × 103 s–1(10%) and yielding a photochromic effect at positive polarization.

Nanostructured TiO2 semiconductor electrodes modified with surface-attached viologens: applications for displays and smart windows

Viologen derivatives adsorbed on TiO2 surfaces in nanocrystalline-nanoporous electrodes have been studied with respect to electrochromic phenomena. The transparent nature and the high internal surface area of these electrodes are very beneficial for this purpose. Two different viologens were studied giving rise to blue, green, and violet coloration. For one of the viologens we show the possibility to vary the color for the same viologen/TiO2 electrode from transparent to green or violet depending on the applied potential. Depending on the applied potential different optical densities were obtained. Optical density changes from 0.1 up to 1 and coloration efficiencies above 100 cm2C-1, with a maximum value of 440 cm2C-1, were obtained. The switching times for these electrodes for both coloration and bleaching were faster than 1s for a transmittance change larger than 60%, using 0.5M LiClO4 in acetonitrile as electrolyte. Preliminary stability tests were performed. One electrode has been cycled 654 times without substantial decline in coloration efficiency.