Time-resolved luminescence spectroscopy of self-trapped excitons in ladder type Br-bridged Pt complexes

The out-of-phase and in-phase ladder type Br-bridged Pt complexes are investigated by time-resolved luminescence spectroscopy in pico- and femtosecond time regions. The observed luminescence spectra have peaks at 0.87 and 0.94 eV in out-of-phase and in-phase materials, respectively, and are assigned to self-trapped excitons. The wave-packet oscillations in self-trapped excitons (STE) are observed in both materials. The time-evolution curves are analyzed in terms of the secondary radiation theory of strongly coupled electron-phonon system. The period and dephasing time of oscillations as well as the lifetime and spectral shape of the STE luminescence are determined. The fast dephasing or cooling of the wave-packet motion observed in the in-phase type complex is ascribed to inter-chain interactions within the ladder.