W. H. F. Sasse

Colloidal platinum sols: preparation, characterization and stability towards salt

Stable aqueous colloidal platinum sols have been prepared by the citrate reduction of chloroplatinic acid. Particle size at the completion of the reaction was found to increase with increased heat input during reduction. The u.v.–visible spectrum of the platinum sols depends upon particle size up to 4 nm. A stirring–centrifugation procedure was used to identify the extent of coagulation induced by added electrolytes. It was found that the smaller platinum particles required higher concentrations of added electrolyte before being destabilized. A survey was made of the coagulation of the platinum sols induced by mono-, di- and tri-valent cations.Hydrogen treatment of platinum sols leads to growth of particles up to a maximum size of ca. 5 nm and substantial linkage of primary particles to form extensive aggregates. Such growth and aggregation lead to significant changes in the u.v.–visible spectra and reduced resistance to electrolyte-induced coagulation.

RAFT synthesis of linear and star-shaped light harvesting polymers using di- and hexafunctional ruthenium polypyridine reagents

The syntheses of linear and star-shaped light harvesting polymers with well defined structure and narrow molecular weight distribution are described. These polymers have ruthenium polybipyridine moieties as the energy trap cores and styrene functionalized coumarin monomers as the light absorbing antenna chromophores. The polymers have been made by reversible addition–fragmentation chain transfer (RAFT) polymerisation using di- or hexafunctional ruthenium-containing RAFT agents. The resulting ruthenium-containing polymers have narrow molecular weight distribution (polydispersity < 1.1) and exhibit energy transfer efficiencies of up to 60% between the coumarin donor dyes and the ruthenium acceptor chromophores.

XANTHENE DYES AS SENSITIZERS FOR THE PHOTOREDUCTION OF WATER

Abstract— Some photochemical and photophysical properties of a group of xanthene dyes have been studied in relation to their roles as sensitizers for the photoreduction of water. New spectroscopic and kinetic measurements have been carried out with these dyes. The triplet states of the dyes undergo energy‐transfer and electron‐transfer, but with rate constants differing by two orders of magnitude in favour of the former pathway. The very efficient transfer of triplet energy from a group of dyes to an acceptor molecule led to the design of a greatly improved system for the photochemical production of hydrogen.

Singlet and triplet energy transfer processes in ruthenium(II) bipyridine complexes containing covalently bound arenes

Abstract Singlet and triplet energy transfer processes in [Ru(bipy) 2 (4-methyl-4′-(2-arylethyl)-2,2′-bipyridine)] 2+ have been investigated, where aryl = 2-naphthyl (Ru-Naph), 9-anthryl (Ru-Anth) and 1-pyrenyl (Ru-Pyrene). In each case fluorescence from the aromatic chromophore is quenched by intramolecular energy transfer to Ru(bipy) 3 2+ whereas emission from the Ru(bipy) 3 2+ moiety is controlled by the relative energy of its 3 MLCT state and the pendant arene triplet states. Consequently 3 MLCT emission is observed for Ru-Naph whereas it is fully quenched for Ru-Anth. When the two states are isoenergetic (e.g. Ru-Pyrene) a long-lived 3 MLCT emission is observed which delays with the same lifetime as the pyrene triplet state (5.23 μs).

Highly efficient photoreduction of water using energy transfer

Abstract The photochemistry of the system water-tris(2,2′-bipyridine)ruthenium(II) dication—9-anthracenecarboxylate anion—methylviologen—ethylenediaminetetraacetic acid—platinum has been studied. Efficient triplet energy transfer from the excited ruthenium complex to the anthracene derivative leads to the formation of hydrogen in quantum yields up to 0.85.

The 9-anthracenecarboxylate anion as sensitizer for the photoreduction of water

Abstract Methylviologen quenches the excited singlet and triplet states of the 9-anthracenecarboxylate anion with high efficiency; only the triplet state produces a high yield of th methylviologen radical cation which can reduce water to hydrogen.

Localization of electronic excitation energy in Ru(2,2′-bipyridine)2(2,2′-bipyridine-4,4′-dicarboxylic acid)2+ and related complexes

Abstract The absorption spectra of Ru(2,2′-bipyridine) 2 (2,2′-bipyridine-4,4′-dicarboxylic acid) 2+ (I) and its diethyl ester (II) are closely related and are both significantly different from the spectra of the mono-protonated (Ia) and deprotonated (Ib) complexes. Luminescence polarization measurements show that for I and II the luminescent states have the transferred electron in the bipy-4,4′(COOH) 2 and bipy-4,4′(COOEt) 2 ligands, respectively, rather than in the unsubstituted bipy ligands.

Macrobicyclic chromium(III) hexaamine complexes

Le compose cristallise dans le systeme monoclinique, groupe P2 1 /c avec Z=4. Coordination octaedrique autour du cation. Etude electrochimique et photochimique

PHOTOPRODUCTION OF HYDROGEN FROM LINKED CHROMOPHORES

Abstract On irradiation of solutions of anthryl‐substituted cobalt(III) cage complexes, [(l‐(anthryl‐9‐methylamino)‐8‐methyl‐3,6,10,13,16,19‐hexaazabicyclo [6.6.6] eicosane) cobalt(III)]3+ or [(l‐(4‐an‐thryl‐9)‐3‐aza‐butyl‐l‐amino)‐8‐methyl‐3,6,10,13,16,19‐hexaazabicyclo [6.6.6] eicosane)cobalt (III)]3* in the presence of ethylenediaminetetraacetic acid and platinum catalysts hydrogen was produced. These complexes act as coupled photosensitizers (anthracene moiety) and electron relays (cobalt cage) to produce H2via energy trapping and intramolecular electron transfer initially. The intensity of fluorescence and the photochemical reactivity favour the latter complex and the excited singlet state of the anthracene chromophore is invoked as the intermediate state leading to the reduction of Co(III) to Co(II).

New inhibitors of auxin transport

3-Phenacylidinphthalid und dessen Hydrat verursachen einen konzentrationsabhängigen Verlust der geotropischen Reaktion der Wurzel und die Aufhebung der Apikaldominanz des Sprosses. Es wird nachgewiesen, dass die beiden Substanzen primär den basipetalen Transport des endogenen Auxins hemmen.