Ultrafast optical response in a quasi-one-dimensional halogen-bridged mixed-valence complex [Pt(en) 2][PtBr 2(en) 2](ClO 4) 4

Abstract

Ultrafast optical response in a quasi-one-dimensional halogen-bridged mixed-valence complex [Pt(en) 2][PtBr 2(en) 2](ClO 4) 4 (en=ethylenediamine) has been investigated by femtosecond absorption spectroscopy at room temperature using pump-probe spectroscopy. The photo-induced absorption around 1.3 eV and the bleaching from 1.5 eV to 2.7 eV were observed. Both consist of a fast-decay component due to STEs and a slow-decay component due to polaron pairs. The former decays exponentially with the time constant of 1.4±0.1 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.