Stabilizer photophysical studies

Photophysical Studies of Ultraviolet Stabilizers, Particularly in the 2-Hydroxyphenyl Benzotriazole Class... 

The quantum yields are 0.15-0.21 in ethanol and 0.01-0.02 in an aqueous medium, but in micelles, the quantum yields are five to tenfold increased. The aggregation of these dyes was studied in [53]. The amphiphilic squaraines 4 combine favorable photophysical properties and good solubility in aqueous media and in addition interact efficiently with micelles, and therefore have the potential to be used as NIR fluorescent sensors. However, our own investigations show that aniline-based squaraines lack chemical and photochemical stability when compared to oxo-squaraines with heterocyclic end-groups. 

Ionic liquids are a class of solvents and they are the subject of keen research interest in chemistry (Freemantle, 1998). Hydrophobic ionic liquids with low melting points (from -30°C to ambient temperature) have been synthesized and investigated, based on 1,3-dialkyl imidazolium cations and hydrophobic anions. Other imidazolium molten salts with hydrophilic anions and thus water-soluble are also of interest. NMR and elemental analysis have characterized the molten salts. Their density, melting point, viscosity, conductivity, refractive index, electrochemical window, thermal stability, and miscibility with water and organic solvents were determined. The influence of the alkyl substituents in 1,2, 3, and 4(5)-positions on the imidazolium cation on these properties has been scrutinized. Viscosities as low as 35 cP (for l-ethyl-3-methylimi-dazolium bis((trifluoromethyl)sulfonyl)amide (bis(triflyl)amide) and trifluoroacetate) and conductivities as high as 9.6 mS/cm were obtained. Photophysical probe studies were carried out to establish more precisely the solvent properties of l-ethyl-3-methyl-imidazolium bis((trifluoromethyl)sulfonyl)amide. The hydrophobic molten salts are promising solvents for electrochemical, photovoltaic, and synthetic applications (Bon-hote et al., 1996). 

One of the most studied mononuclear systems that usually leads to supramolecular networks and that also exhibits very rich photophysics and photochemistry is the [Au (CN)2] anion. This complex is among the most stable two-coordinate complexes of the transition ions, with a stability constant of 1037 [9], being reasonably stable to air, moisture, temperature and light, which could make it appropriate for practical applications. 

Most photosensitizers, however, are reasonably photostable compounds, and their optical properties have been studied in depth. In particular, there has been much interest in ruthenium-based photosensitizers such as [Ru(bpy)3]2+ and [Ru(phen)3]2+, due to their stability and absorption of visible light. Detailed information on their optical properties, including ground and excited state information in relation to photosensitization, has been reviewed by Creutz et al. [16]. Similarly, the photochemistry and photophysics of rhenium complexes, as discussed here, have been reviewed in detail by Kirgan et al. [7]. 

Rubpy is an often used shorthand for the well studied [Ru(bpy)3]2+ complex cation and is also used more loosely to refer to any Ru(D) polypyridyl complex with similar properties. As shown in Fig. 7, the three best studied members of the Rubpy family are the parent complex, [Ru(bpy)3]2+, the phenanthroline analogue, [Ru(phen)3]2+, and the bis terpy complex, [Ru(terpy)3]2+, which has less optimal photophysical properties but has a number of synthetic and stereochemical advantages. The synthe sis, stability and photophysics of Rubpy complexes has been reviewed many times17 54 57 and the highlights of these properties as related to artificial photosynthetic assemblies is summarized here. 

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