Reversible light-induced magnetization change in an azobenzene-attached pyridylbenzimidazole complex of iron(II) at room temperature.

Reversible photomagnetic effects were demonstrated at room temperature by the use of a new iron(II) complex t100c0-[Fe()3](BF4)(2).3H2O ( =phenyl(2-pyridin-2-yl-3H-benzoimidazol-5-yl)diazene), based on the strategy of the so-called "ligand-driven light-induced spin change" (LD-LISC) effect. The complex showed thermal spin crossover in both solid and solution states, showing a transition temperature T1/2=279(16) K in acetone. trans-cis Photoisomerization of azobenzene moieties using different energy lights afforded reversible photomagnetic effects, which were directly determined using the Evans 1H NMR method.