Abstract
The absorption and emission properties of di(3-pyridyl)ketone have been studied in aqueous solution as a function of pH and the p Ks of the nitrogen protonated mono- and di-cations have been spectrophotometrically determined. This molecule exhibits room temperature and low temperature phosphorescence emission of n, π* character in the whole acidity range explored [pH 9/(H 0 − 9)]; triplet lifetime has been measured from the phosphorescence intensity decay. An unusual trend of phosphorescence intensity and lifetime as a function of pH was found and was interpreted as due to hydrogen bond formation with the solvent, whose entity is influenced by both structure breaking of water and protonation of the nitrogen atoms caused by decreasing pH. Experiments carried out in the presence of sodium acetate are described which support this hypothesis. Comparison of the results obtained with those for benzophenone and phenyl(3-pyridyl)ketone allows some generalizations to be drawn about the influence of the heteroatom on the photophysics of ketones.
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