Time-resolved photoluminescence study of excitonic relaxation in one-dimensional systems

Self-trapped exciton luminescence of quasi-one-dimensional (1D) halogen-bridged mixed-valence platinum complexes [Pt(II)(EA)₄] [Pt(IV)Cl₂{(EA)}₄$] ${Cl}₄·4{H}₂$O (EA = ethylamine) and [Pt(II)${(en)}₂$] [Pt(IV)${Cl}₂(en)₂] (ClO₄)₄ (en = 1,2-diaminoethane) are studied by time-resolved photoluminescence experiments. The lifetimes of the luminescence of self-trapped excitons are exceptionally short, of the order of 100 psec. We interpret the short lifetime by a "gaint oscillator strength" caused by a strong coupling between the electron and hole of the 1D charge transfer exciton and an extended polaronlike character of the 1D state. The lifetimes of the broad luminescence and of the resonant Raman lines during the barrier-free relaxation process are both faster than 7 psec.