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 photo-isomerization switches on and off some emission bands of 1 and provides a means of externally manipulating the magnetic properties of the assembly.