Silica–[Fe(bpy)3]2+ composite particles with photo-responsive change of color and magnetic property

Photo-induced complex formation of tris-2,2′-bipyridine iron(II) complex ([Fe(bpy)3]2+) from the mixture of FeCl3 and 2,2′-bipyridine was achieved in silica gel containing 150–300 μm silica particles, derived from a complex emulsion with HCl aqueous solution and tetraethyl orthosilicate (TEOS). More than 95% of Fe(III) and 2,2′-bipyridine were incorporated in silica particles. Yellow-red color change, due to [Fe(bpy)3]2+, was observed by irradiation with 365 nm UV beam at 0.3 mW cm−2 for 120 s. The complex formation accompanies simultaneous spin transition from the high-spin state of Fe(III) to the low-spin state of Fe(II).