Observation of the wave-packet oscillation during the exciton self-trapping process in a quasi-one-dimensional halogen-bridged Pt complex

Using femtosecond time-resolved luminescence spectroscopy, we have observed a wave-packet oscillation in an adiabatic potential well associated with a self-trapped exciton (STE). We have investigated the STE luminescence band of a quasi-one-dimensional halogen-bridged platinum complex $\left[{\mathrm{Pt}\left(\mathrm{en}\right)\mathrm{}}_2\right]\left[{\mathrm{Pt}\left(\mathrm{en}\right)\mathrm{}}_2{\mathrm{Br}}_2\right]({\mathrm{ClO}}_4{)}_4.$ In the time evolution of the luminescence, we have observed an oscillation with a period of about 300 fs. This result shows the formation of a wave packet and its oscillation, which is damped with the time constant of about 430 fs. The STE’s have a lifetime of about 5.5 ps at room temperature.