title: LED-illuminated NMR studies of flavin-catalyzed photooxidations reveal solvent control of the electron-transfer mechanism.
abstract: Mechanistic insights into chemical photocatalysis are mainly the domain of UV/Vis spectroscopy, because NMR spectroscopy has been limited by the type of illumination so far. An improved LED-based illumination device can be used to obtain NMR reaction profiles of photocatalytic reactions under synthetic conditions and perform both photo-CIDNP and intermediate studies. Flavin-catalyzed photooxidations of alcohols show the potential of this setup. After identical initial photoreaction steps the stabilization of a downstream intermediate is the key to the further reaction mechanism and the reactivity. As a chemical photocatalyst flavin can act either as a one- or a two-electron mediator when the stability of the zwitterionic radical pair is moldulated in different solvents. This demonstrates the importance of downstream intermediates and NMR-accessible complementary information in photocatalytic reactions and suggests the control of photoorganic reactions by solvent effects.
authors.affiliation: Institut für Organische Chemie, Universität Regensburg, 93040 Regensburg (Germany).
authors.forename: Christian
authors.initials: C
authors.lastname: Feldmeier
authors.forename: Hanna
authors.initials: H
authors.lastname: Bartling
authors.forename: Kathrin
authors.initials: K
authors.lastname: Magerl
authors.forename: Ruth M
authors.initials: RM
authors.lastname: Gschwind
keywords: NMR spectroscopy; UV/Vis spectroscopy; flavin; photocatalysis; solvent effects