Ultrafast dynamics of lattice relaxed states in quasi-one-dimensional MX-chain compounds

Ultrafast relaxation processes of photoexcited states in a quasi-one-dimensional halogen-bridged mixed-valence metal complex [Pt(en)2][Pt(en)2I2](SO4)2.6H2O have been investigated by femtosecond transient absorption spectra measurements. A photoinduced absorption band caused by non-thermalized self-trapped excitons has been found. Oscillation of the absorption band caused by the symmetric Pt–I stretching mode of the self-trapped exciton with a frequency of 103 cm−1 has been observed. The rise time of a polaron absorption band has been measured to be 1.2 ps. This corresponds to the decay time, 1.1 ps, of a photoinduced absorption band which oscillates with a frequency of 74 cm−1.