Real-time capturing of the nuclear wave-packet shape in self-trapped excitons.

We measured the time evolutions of the luminescence spectra in a quasi-1D halogen-bridged platinum complex [Pt(en)(2)][Pt(en)(2)Br(2)](ClO4)(4) with a 50 fs resolution up-conversion spectroscopy and succeeded in real-time visualization of the shape of the wave packet (WP) propagating on the adiabatic potential surface of a self-trapped exciton. The behavior of the WP is in excellent agreement with a calculation based on a harmonic oscillator. We have found that the damping of the WP oscillation is highly nonexponential.