Light-controlled switching of the spin state of iron(III).

Controlled switching of the spin state of transition metal ions, particularly of Fe and Fe, is a prerequisite to achieve selectivity, efficiency, and catalysis in a number of metalloenzymes. Here we report on an iron(III) porphyrin with a photochromic axial ligand which, upon irradiation with two different wavelengths reversibly switches its spin state between low-spin (S = /) and high-spin (S = /) in solution (DMSO-acetone, 2:598). The switching efficiency is 76% at room temperature.