A polymer matrix isolation technique was examined as a potentially novel strategy for realizing optically switchable materials. Not only was a ferricinium ion ([Cp2FeIII](+)) produced, but also was produced an isomer of ferrocene (Cp2Fe) with high spin Fell in a poly(methyl methacrylate) (PMMA) matrix film containing CCl4 by the photoillumination of ferrocene at low temperature. The high spin state could be maintained for an extended period when the sample was kept below approximate to 130 K. This is the first observation of a photoinduced spin transition for ferrocene. The strategy that we used to achieve the spin transition using optical stimuli may open up many possibilities for the development of new magneto-optical devices.