Enantioselective Magneto-Chiral Photochemistry Rediscovered

Enantioselective magneto-chiral photochemistry (MChPh), which represents the ability of an unpolarized light beam <i><b>k</b></i> applied along a magnetic field <i><b>B</b></i> to produce an enantiomeric excess (<i>ee</i>), was experimentally demonstrated for the first time 25 years ago. Despite the relevance that this effect can have for the origin of molecular homochirality, no other experiment has been reported in the literature since then. With the aim of reexploring this enantioselective photochemical reactivity and quantitatively determining the <i>ee</i> achievable through MChPh as a function of the applied magnetic field and the laser irradiation wavelength, we report here on new magneto-chiral dichroism (MChD) studies and MChPh experiments on potassium tris-(oxalato)-chromate-(III). By irradiating a racemic mixture of enantiomers in solution (<i>T</i> = 5 °C) at λ = 695.5 nm (500 mW), the wavelength where MChD is maximum, under a magnetic field <i><b>B</b></i> = 30 T for 30 min, an <i>ee</i> of 0.50% has been obtained. We demonstrate that under the same experimental conditions, circularly polarized photochemistry (CPPh), the most accredited mechanism at the origin of molecular homochirality, yields a lower <i>ee</i>.