Femtosecond dynamics of self-trapped excitons in quasi-one-dimensional halogen-bridged Pt complexes

Dynamics of the self-trapped excitons (STE) in quasi-one-dimensional haloge n-bridged mixed-valence platinum complexes [Pt(en)(2)][Pt(en)(2)X-2](ClO4)( 4) (en = ethylenediamine, X = Cl or Br) has been studied by luminescence up conversion technique. Time evolution of the luminescence from STE has been studied from 0.79 to 2.1 eV in the X = Cl system with a time resolution of 180 fs. The cooling time of hot STEs was determined as 210 fs, and the form ation time of STE was found to be shorter than 140 fs, which is limited by our time resolution. In the X = Br system, we achieved a time resolution of 90 fs and succeeded in observing the wave packet oscillation in the adiaba tic potential well of STE by luminescence for the first time. The period of the local mode oscillation is 290 fs (97 cm(-1)) and the damping time cons tant is 430 fs. Usefulness of the up-conversion spectroscopy for wave packe t observation is demonstrated. (C) 1999 Elsevier Science B.V. All rights re served.