Ultrafast Vibrational Dynamics in a Quasi-One-Dimensional System: Femtosecond Impulsive Excitation of the PtBr(ethylenediamine) Mixed-Valence Linear Chain Complex

Abstract

We have used femtosecond impulsive excitation to time-resolve the vibrational motions following the excitation of the optical intervalence charge transfer transition in a quasi-one-dimensional molecular solid, the mixed-valence metal−halide linear chain complex [Pt(en)2][Pt(en)2Br2]·(PF6)4 (en = ethylenediamine, C2H8N2). Wavelength-resolved measurements reveal an induced absorption signal assigned to the formation of the self-trapped exciton that is strongly modulated by vibrational wavepacket oscillations originating on both the ground and excited electronic states. The ground-state response, which includes the fundamental chain axis symmetric stretch frequency and its harmonics, is discussed in terms of resonantly enhanced impulsive stimulated Raman excitation of a strongly coupled electron−phonon system.