Ultrafast Optical Response in Quasi-One Dimensional Halogen-Bridged Mixed-Valence Complexes [Pt(en)2][PtBr2(en)2](ClO4)4and [Pd(en)2][PdCl2(en)2](ClO4)4

Abstract

Abstract Ultrafast optical response in two quasi-one-dimensional halogen-bridged mixed-valence complexs [Pt(en)2][PtBr2(en)2](ClO4)4 (en=ethylenediamine) (abbreviated as PtBr) and [Pt(en)2][PtBr2(en)2](ClO4)4 (as PdCl) has been investigated by femtosecond absorption spectroscopy at room temperature by pump-probe spectroscopy. The photo-induced absorption around 1.3 eV and the bleaching from 1.5 eV to 2.7 eV were observed in PtBr. Both consist of a fast-decay component due to STEs and a slow-decay component due probably to polaron pairs. The former decays exponentially with the time constant of 1.4 ± 0.2 ps. The latter decays as erf(t β) with β = -0.22 ± 0.02, indicating the geminate recombination of an electron polaron and a hole polaron after moving freely along the chain. The deviation of β from the ideal random-walk model (β = -0.5) is explained by introducing the effect of potential barrier between the polarons hindering the recombination. A pump-probe absorption spectrum of PdCl is obtained from the ...