Prof. O. Wenger: "Understanding and controlling elementary reaction steps in photocatalysis"

Organisch-chemisches Kolloquium

Das Institut für Organische Chemie lädt ein zum Vortrag von

Prof. Dr. Oliver Wenger, Universität Basel

mit dem Titel:

"Understanding and controlling elementary reaction steps in photocatalysis"

Abstract:

Today’s molecular photochemistry is making faster progress in the empirical discovery of new types of reactions than in the fundamental understanding of the underlying elementary processes. Mechanistic studies become increasingly important if the field is to advance. This presentation will focus on two poorly understood fundamental aspects: (1) the role of cage escape in the energy efficiency of photoredox catalysis and (2) the photoreactivity of excited radical ions with picosecond lifetimes.

Photoinduced electron transfer results in a radical pair being embedded in a so-called “solvent cage”, from which the individual radicals must escape in order to form stable photochemical products. The quantum yield for cage escape is generally not unity, and therefore successful photoinduced electron transfer does not imply successful photoproduct formation. In three benchmark photoreactions, we found that the rates and quantum yields of photoproduct formation correlate with the quantum yields of cage escape.

Radical ions have excited states with picosecond lifetimes that are too short for bimolecular diffusion-controlled photoreactions, yet excited radical ions are often considered important catalytic species. We found direct evidence of picosecond photochemistry in aggregates composed of radical ions and substrate molecules. This suggests that excited radical ions, rather than photo-degradation products, may actually be responsible for the observable photoreactivity, at least in some favorable cases.