No abstract

During the oxidative degradation of 2,4-dimethylaniline (2,4-xylidine) by means of the H2O2/UV method, a series of hydroxylated aromatic amines are formed, this result confirming the role of the hydroxyl radical as an initiator of the oxidative chain reaction. Thermal or photochemically enhanced Fenton reactions in the presence of 2,4-dimethylaniline (2,4-xylidine) yield primarily 2,4-dimethylphenol as an intermediate product, the genesis of which may only be explained by an electron transfer mechanism. Experimental evidence for such a mechanism is presented, and values for the quantum yields of the photochemically enhanced reduction of iron(III) to iron(II) in aqueous solutions of 2,4-xylidine are given.

This glossary of terms covers phenomena considered under the very wide terms photocatalysis and radiation catalysis. A clear distinction is made between phenomena related to either photochemistry and photocatalysis or radiation chemistry and radiation catalysis. The term "radiation" is used here as embracing electromagnetic radiation of all wavelengths, but in general excluding fast-moving particles. Consistent definitions are given of terms in the areas mentioned above, as well as definitions of the most important parameters used for the quantitative description of the phenomena. Terms related to the up-scaling of photocatalytic processes for industrial applications have been included. This Glossary should be used together with the Glossary of terms used in photochemistry, 3 rd edition,

(1 5. I. 96) In the context of our studies on ruthenium(I1) complexes containing polyazaheterocyclic ligands, we have determined the rate constants of quenching by molecular oxygen (k,) of the metal-to-ligand charge-transfer-excited state of a series of homoleptic [RuL,] complexes (where L stands for 2,2'-bipyridine (bpy), I,l0-phenanthroline (phen), 2,2'-bipyrazine (bpz), 4,7-diphenyI-l,lO-phenanthroline (dip), diphenyl-l,IO-phenanthroline-4,7-disulfonate (dpds), and l,l0-phenanthroline-5-octadecanamide (poda)) in H20 and in MeOH. These compounds are singlet-oxygen ( 0 2 ( ' A g ) ) sensitizers, and quantum yields of singlet-oxygen production (Gd) in both solvents are also Ag)), the lowest electronically excited state of the oxygen molecule, is a highly reactive species and a key intermediate in chemical and biological processes, such as photooxidation reactions, DNA damage, and photodynamic therapy of cancer [l-51. Most often, singlet oxygen is produced by photosensitization involving electronic-energy transfer from the triplet excited state of a sensitizer (generally a dye) to ground-state molecular oxygen. Investigations on sensitizers able to produce efficiently singlet oxygen, as well as studies aimed at elucidating the role of the solvent or the surrounding medium, are of great interest because of the importance of singlet oxygen in both photochemical and photobiological applications.Coordination compounds of Ru" with polyazaheteroaromatic chelating ligdnds have attracted considerable attention during the last fifteen years. This is due to the unique combination of their spectroscopic, redox, and photochemical features, together with the possibility of 'fine tuning' their properties by a judicious choice of the type, number, and substituents of the heteroaromatic chelating ligands of the metal coordination sphere [6]. The excitation of Ru" chelate complexes in the 180-550-nm spectral region is followed by a fast intersystem crossing leading to the formation of the metal-to-ligand charge-transfer