André Henrion

The deactivation behaviour of photoexcited 2,6-diphenyl-4-(p-dimethylaminophenyl)-benzoylimino-pyridinium ylide

Abstract The photophysical and photochemical deactivation behaviour of 2,6-di-phenyl-4-( p =dimethylaminophenyl)-benzoyliminopyridinium ylide as a model compound of N -ylides has been studied. The solvent has a marked influence on its absorption and fluorescence spectra and also on its photophysical and photochemical deactivation behaviour. A deactivation scheme is discussed in the light of fluorescence lifetime and quantum yield measurements. The main radiationless deactivation process in protic solvents involves torsional relaxation and is viscosity dependent. In solvent of moderate polarity it is postulated that the formation of a valence isomer diminishes the population of the fluorescing state. The influence of the solvent can be described by means of the multiparameter model of Kamlet and Taft. The photochemical NN bond cleavage originates from the triplet state but the intramolecular rearrangement to the 1,2-diazepine occurs in the singlet state. The properties of the solvent determine which of the two photoreaction predominates.

Statistical estimation of the influence of mineralization methods on the results of heavy metals determination in cereals by the DPASV method

SummaryThe elements Cd, Cu, Pb and Zn have been determined in wheat, barley and oats by differential pulse anodic stripping voltammetry after wet mineralization, mineralization by dry ashing or mineralization in a PTFE bomb. The procedures are described. The results were evaluated by BASIC programs for one dimensional data evaluation, by principal components plot and by multidimensional analysis of variance. The influences of mineralization procedures on the results are low compared with the different contents in the three cereals particularly for Cd, but also for Pb and Zn. There are no significant differences, in the Cu content.