Photoinduced Phase Transition to a New Macroscopic Spin-Crossover-Complex Phase

We clarified for the first time that the photoinduced phase is quite different in structure from the thermally induced phase by the resonant Raman spectroscopy in the spin-crossover complex, $\left[\mathrm{Fe}\right(2-\mathrm{pic}{)}_3]-{\mathrm{Cl}}_2\mathrm{EtOH}$. In the photoinduced phase we observed a number of additional lines assigned to infra-active vibrational modes which are strongly prohibited by selection rules in the thermally induced phase. These results indicate that a dramatic symmetry lowering should take place in the photoinduced phase. The cooperative Jahn-Teller transformation is a plausible candidate for the symmetry lowering in the photoinduced phase.