Comparative time-resolved photoconductivity and absorption spectroscopy studies on dark secondary reactions following the photoreduction of benzophenone by triethylamine

The dark secondary reactions following the photoreduction of benzophenone by triethylamine constitute an example of tricky reactions involving radicals throughout proton, hydrogen atom and electron transfer. In this work, nanosecond transient absorption spectroscopy is used to detect the influence of hydrogen bonding ability of the solvent on these reactions by means of adding water or methanol to acetonitrile solutions. The effect of increasing polarity is studied with the addition of LiClO4 and it is found at this occasion that dark processes are also sensitive to Lewis acid-base properties of the solvent. The secondary reactions in the reference medium, i.e., neat acetonitrile, are conveniently monitored by photoconductivity technique, which reveals to be a useful complement to absorption spectroscopy and underlines the crucial role of residual water on the reactions. (C) 1999 Elsevier Science S.A. All rights reserved.