14-O-04-Silver ions and quantum-sized silver sulfide clusters in zeolite A

This chapter presents silver ions and quantum-sized silver sulfide clusters in zeolite A. Ultraviolet/visible (UV/vis) spectroscopic studies of Ag+xNa+12-xA, Ag+xCa26-0.5xA Ag+9.5A in conjunction with molecular orbital calculations lead to the result that four-ring coordinated Ag+ is responsible for the deep yellow color observed in silver-loaded zeolite A activated at room temperature. Electronic transitions can be interpreted as charge transfer from zeolite oxygen lone pair to Ag+. The reaction of hydrogen sulfide (H2S) with activated Ag+-loaded zeolite A leads to the formation of quantum-sized, luminescent silver sulfide clusters inside the zeolite cavities. The cluster size can be varied by adjusting silver loading

Luminescence properties of Ag2S and Ag4S2 in zeolite A

Silver sulfide particles of different size are synthesized in the cavities of zeolites A and ZK-4 by exposing the Ag+-exchanged dehydrated zeolites to H2S. The two smallest stable particles synthesized by this method are the Ag2S molecule and the Ag4S2 cluster. Both show photoluminescence in the visible region. The luminescence properties of the samples are studied as a function of temperature, of the silver sulfide content, and of the co-cations. By using the Ca2+-exchanged form of zeolite A it is possible to synthesize silver sulfide-zeolite systems which contain Ag2S and Ag4S2 in the same zeolite crystal. After excitation with UV light energy transfer from the excited Ag2S to Ag4S2 most probably occurs. These systems are potential materials for thermometry because their luminescence properties strongly depend on the temperature

Quantum-sized silver, silver chloride and silver sulfide clusters

Thin AgCl layers photocatalytically oxidize water to O2 under appropriate conditions. The photoactivity of AgCl extends from the UV into the visible light region in a process known as self-sensitization, which is due to the formation of silver during the photoreaction. This silver can be almost quantitatively reoxidized electrochemically, making it feasible that a thin AgCl layer deposited on a conducting substrate can be used as a photoanode for water splitting if coupled with an appropriate photocathode. The silver chloride/silver cluster phase boundary plays a decisive role in the photocatalytic silver chloride electrode system. We have therefore studied this interphase by means of quantum chemical calculations from which we report first results, specifically for the (Ag)115(AgCl)192 composite. Clusters of semiconducting materials are interesting considering their application as a photocathode in such a device. In this context, we also report the synthesis and properties of luminescent quantum-sized silver sulfide clusters in the cavities of zeolite A. The color of the silver sulfide zeolite A composites ranges from colorless (low loading) to yellow–green (medium loading) to brown (high loading). A low silver sulfide content is characterized by a blue–green luminescence and distinct absorption bands, while samples with medium or high silver sulfide content show an orange or red colored emission and a continuous absorption

Preparation and characterization of 3-(4,5-ethylenedithio-1,3-dithiol-2-ylidene)naphthopyranone: a luminescent redox-active donor–acceptor compound

A new 1,3-dithiol-2-ylidene substituted naphthopyranone 2 has been synthesized and characterized. UV–vis spectroscopic and cyclic voltammetry results, interpreted on the basis of density functional theory, show that 2 displays an intramolecular charge-transfer transition and acts like a donor–acceptor (D–A) system. Furthermore, a weak fluorescence originating from the excited charge-transfer state is observed

Synthesis of new ethynylbipyridine-linked mono- and bis-tetrathiafulvalenes: electrochemical, spectroscopic and Ru(II)-binding studies

Two new ethynylbipyridine-linked mono- and bis-tetrathiafulvalene (TTF) derivatives, together with a Ru(II) complex, were synthesized using Sonogashira coupling reactions and characterized by UV/vis spectroscopy and cyclic voltammetry. They display a clear electrochemically amphoteric behavior consisting of two reversible single-electron oxidation waves (typical for TTF derivatives) and one reversible single-electron reduction wave (bpy) and act as donor–acceptor (D–A) systems. Furthermore, for the Ru(II) complex, a quite intense fluorescence originating from the 3MLCT state is observed

Fused Donor-Acceptor Ligands in Ru(II) Chemistry: Synthesis, Electrochemistry and Spectroscopy of [Ru(bpy)3-n(TTF-dppz)n](PF6)2 (n = 1-3, TTF-dppz = 4 ,5 -bis(propylthio)tetrathiafulvenyl[i]dipyrido[3,2-a:2 ,3 -c]phenazine)

Three ruthenium(II) polypyridine complexes of general formula [Ru(bpy)3-n(TTF-dppz)n](PF6)2 (n=1-3, bpy=2,2-bipyridine), with one, two or three redox-active TTF-dppz (4,5-bis(propylthio)tetrathiafulvenyl[i]dipyrido[3,2-a:2,3-c]phenazine) ligands, were synthesised and fully characterised. Their electrochemical and photophysical properties are reported together with those of the reference compounds [Ru(bpy)3](PF6)2, [Ru(dppz)3](PF6)2 and [Ru(bpy)2(dppz)](PF6)2 and the free TTF-dppz ligand. All three complexes show intraligand charge-transfer (ILCT) fluorescence of the TTF-dppz ligand. Remarkably, the complex with n=1 exhibits luminescence from the Ru2+dppz metal-to-ligand charge-transfer (3MLCT) state, whereas for the other two complexes, a radiationless pathway via electron transfer from a second TTF-dppz ligand quenches the 3MLCT luminescence. The TTF fragments as electron donors thus induce a ligand-to-ligand charge-separated (LLCS) state of the form TTF-dppz--Ru2+-dppz-TTF+. The lifetime of this LLCS state is approximately 2.3 s, which is four orders of magnitude longer than that of 0.4 ns for the ILCT state, because recombination of charges on two different ligands is substantially slower