Abstract
Time-resolved transient absorption (TRABS) experiments were carried out on a picosecond to nanosecond time scale in order to determine the mechanism of photoinduced hydrogen transfer between benzophenone (Bp) and dimethylaniline (DMA) covalently linked by a methylene chain (Bp(CH 2 ) 3 DMA), abbreviated B3D. The results obtained with the polymethylene-linked system B3D in methylcyclohexane (MCH), acetonitrile (ACN) and isopropanol (i-PrOH) have been compared with earlier investigations on free (unlinked) systems. With B3D in ACN and i-PrOH triplet formation and electron transfer were observed within a time window of 0–9 ns, but no proton transfer was detected. In the non-polar solvent MCH intramolecular hydrogen transfer takes place leading, within 10 ns, to the ketyl radical, but with no radical ion formation as an intermediate reaction. These results are different from investigations reported on free systems, where radical ion formation is regarded as a requirement for subsequent efficient ketyl radical formation. Inferences can be drawn from this study which point to the greater importance of relative geometrical orientation in hydrogen or proton transfer reactions compared with electron transfer reactions.
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