Wave Packet Dynamics in a Quasi-One-Dimensional Metal-Halogen Complex Studied by Ultrafast Time-Resolved Spectroscopy

An ultrafast optical response is studied in a quasi-one-dimensional halogen-bridged mixed-valence metal complex $\left[\mathrm{Pt}\right(\mathrm{en}{)}_2\left]\right[\mathrm{Pt}\left(\mathrm{en}{)}_2{\mathrm{I}}_2\right]({\mathrm{ClO}}_4{)}_4$ with ultrafast time resolution. Wave packet motions both in the ground and self-trapped exciton (STE) states are observed as oscillatory modulations in the time-resolved reflectivity. The wave packet motion on the STE potential surface begins after about 50 fs with respect to the photoexcitation. This delay is attributed to the lattice relaxation from the free exciton state to the STE state.