The electrophilic substituent constant sigma(+) was derived from the relative rate constants of the solvolysis of substituted alpha-cumyl chlorides in an acetone/water solvent mixture in the original work by Brown and Okamoto (J. Am. Chem. Soc. 1958, 80, 4979). As an extension of this procedure, we were looking for methods to determine sigma(+) values in nonpolar media. We have calculated the exocyclic charges q(R) for alpha-cumyl cations (R-C(6)H(4)CMe(2)(+)) as a measure of the electron-donating capacity of meta and para substituents. The UV-vis absorption nu(max) of the analogously substituted nitrobenzene derivatives has been used for the experimental measurement of the electron donating capacity of substituents R in nonpolar media. A linear relationship between nu(max) and Deltaq(R) (= q(R-C(6)H(4)CMe(2)(+)) - q(C(6)H(5)CMe(2)(+))) was obtained. A description of the electron-donating capacity in nonpolar media can be achieved both for substituents investigated already and for those for which the experimental determination of sigma(+) has previously been difficult. Special interest was directed to boron-based substituents in which the electron-donating ability is dependent on the coordinational environment of the boron atom.

Solvatochromism of 4‐nitrocatechol (1), tetra‐n‐butylammonium 2‐hydroxy‐4‐nitrophenolate (2), sodium tris(4‐nitrobenzene‐1,2‐diolato)silicate (3a), tetra‐n‐butylammonium tris(4‐nitrobenzene‐1,2‐diolato)silicate (3b), pyrrolidinium tris(4‐nitrobenzene‐1,2‐diolato)silicate (3c), (3‐amino‐1‐propyl)‐bis(4‐nitrobenzene‐1,2‐diolato)silicate (4a), and (N,N‐diethyl‐3‐amino‐1‐propyl)‐bis(4‐nitrobenzene‐1,2‐diolato)silicate (4b) as well as potassium bis(4‐nitrobenzene‐1,2‐diolato)borate (5) has been studied in a set of common solvents. The origin of the solvent‐induced UV/vis band shifts of 1–3c, and 5 has been determined by means of Linear Solvation Energy Relationship (LSER) using the empirical Kamlet–Taft and Catalán solvent parameter sets, respectively. The solvent‐induced UV/vis band shift of the negatively charged moiety of all solvatochromic dyes studied is mainly a function of the hydrogen‐bond donor (HBD) strength and the dipolarity/polarizability of the solvent as shown by multiple regression analyses. HBD solvents cause a hypsochromic shift of the UV/vis band due to specific solvation of the anion site. Oppositely, increasing dipolarity/polarizability of the solvent induces a bathochromic shift of the UV/vis absorption band. The donor strength of the solvent has an influence on the UV/vis band shift since ion pair formation occurs in solvents of low relative permittivity. This is shown by the impact of the counter ion of sodium tris(4‐nitrobenzene‐1,2‐diolato)silicate (3a) compared to tetra‐n‐butylammonium tris(4‐nitrobenzene‐1,2‐diolato)silicate (3b). The influence of the counter ion on the position of the UV/vis absorption band occurs in the same way as HBD solvents do. Na+ and the pyrrolidinium ion, respectively, have a stronger influence than the tetra‐n‐butylammonium ion on the solvatochromic band shift due to the stronger cation–anion interaction. Copyright © 2008 John Wiley & Sons, Ltd.

The solvatochromism of nine push-pull substituted catechol derivatives has been studied in a set of 39 various solvents. The influence of successive methyl substitution at the catechol OH groups on the extent of the solvatochromic shift has been investigated. The positive solvatochromism of 2-(3,4-dihydroxybenzylidene)-2H-indene-1,3-dione amounts 4360 cm -1 , which ranges from toluene to hexamethyl-phosphoric triamide. To the best of our knowledge, it is one of the largest positive solvatochromic extent measured for a positive solvatochromic dye, comparable with Brooker's thiobarbituric acid with an extent of 4400 cm -1 . The detailed analyses of the solvatochromism were carried out by alternatively using the Kamlet-Taft and Catalán solvent parameters to achieve information of dipolarity versus polarizability effects of solvent upon solvatochromic properties. In solvents with high b values such as alcohols (0.66 < b < 0.90), amides (0.48 < b < 0.80), dimethyl sulfoxide ( b = 0.76), tetramethyl urea (b = 0.80) and hexamethylphosphoric triamide (b = 1.05) UV-Vis absorption spectra show two separate l max , which are caused by a deprotonation reaction. The solvatochromic behaviour of the anionic species is compared with those of the catechol derivatives. Scheme 1. Protonation/deprotonation equilibrium of acceptor-substituted catechols (X = acceptor groups) Scheme 2. Synthesis of catechol-based dyes 2-4

Fluorescent penta-and hexacoordinate silicates were synthesized from 6,7-dihydroxy-4-methylcoumarin (4-methylesculetin, 4-ME), tetramethyl orthosilicate and substituted aminopropylsilanes, respectively. Extinction coefficients, Stokes shifts, and quantum yields of fluorescence were determined and compared * Prof. Dr. S. Spange 1335 with 4-ME. Optical properties of these compounds are sensitive to the polarity of solvents. The fluorescence quenching was investigated in methanol/water mixtures. The title compound sodium tris(4-methylcoumarin-6,7-diolato)silicate (4) shows different behavior from all other compounds investigated.

The aluminium alloys have enormous potentional of weight saving that are drastically gaining importance in the production of transport systems, for example, automobiles, aircraft and aerospace vehicles as well as in production of machines. Owing to the lack of sufficient abrasive wear resistance of aluminium components their application has, so far, been restricted. However, the application range of aluminium components will be extensible through the improvement of the abrasive wear resistance. The main objective of this work is the development of high wear resistant composite coatings on aluminium components by plasma transferred arc (PPA) welding. In this paper the development of the fused tungsten carbide and TiC based composite coatings with a thickness range of a few millimetres is presented. Aluminium alloys are used as matrix material and fused tungsten carbide and TiC are used as hard particles. The weldability of the powder systems with varying welding parameters is examined. The developed coating systems are tested with regard to their specific properties and their wear resistance. Finally, their application potential is presented.