Femtosecond Vibrational Dynamics of Self-Trapping in a Quasi-One-Dimensional System

Abstract

We have directly time resolved the lattice motions associated with the formation of the self-trapped exciton in the quasi-one-dimensional system $[\mathrm{Pt}(\mathrm{en}{)}_{2}][\mathrm{Pt}(\mathrm{en}{)}_{2}{\mathrm{Br}}_{2}]\ifmmode \dot{}\else \.{}\fi{}({\mathrm{PF}}_{6}{)}_{4}$ ( $\mathrm{en}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\mathrm{ethylene}\ensuremath{-}\mathrm{diamine}$, ${\mathrm{C}}_{2}{\mathrm{H}}_{8}{\mathrm{N}}_{2}$), using femtosecond impulsive excitation techniques. A strongly damped, low-frequency wave packet modulation at $\ensuremath{\sim}110{\mathrm{cm}}^{\ensuremath{-}1}$ accompanies the formation of the self-trapped exciton on a $\ensuremath{\sim}200\mathrm{fs}$ time scale following excitation of the intervalence charge-transfer transition. Coherent oscillations at the ground state vibrational frequency and its harmonics are also detected.