A Magneto‐optical Molecular Device: Interplay of Spin Crossover,Luminescence, Photomagnetism,and Photochromism

A bis(pyrazolylpyridyl) ligand, L, containing a central photochromic dithienylethene spacer predictably forms a ferrous Fe₂L₃]⁴⁺ helicate exhibiting spin crossover (SCO). In solution, the compound Fe₂L₃](ClO₄)₄ ( 1 ) preserves the magnetic properties and is fluorescent. The structure of 1 is photo‐switchable following the reversible ring closure/opening of the central dithienylethene via irradiation with UV/visible light. This photoisomerization switches on and off some emission bands of 1 and provides a means of externally manipulating the magnetic properties of the assembly.