Ultrafast lattice relaxation dynamics of photo-excited states in halogen-bridged mixed valence metal complexes

利用飞秒瞬态吸收测量研究了准一维卤素桥混合价络合物（MX化合物）的超快弛豫动力学。在铂化合物中，观察到自陷激子和极化子振动激发态的产生及其向亚稳态的弛豫过程。另一方面，我们发现在时间分辨率（150 fs）内可以产生中性孤子。这被认为是由于势面的耗散性质。结果发现，随着卤离子按Cl、Br和I的顺序在Pt配合物中被取代，STE的弛豫到亚稳态的时间常数和亚稳态STE的衰减时间变短。极化子的产生效率也以相同的数量级增加。这些结果被认为是由于转移能的增加和电子-声子相互作用的减少。发现当铂离子被钯离子取代时，极化子振动激发态的产生效率增加。在Pt-I-化合物中发现了亚稳态附近势面上光生极化子和STE的波包振动，在MX-化合物中发现了奇宇称电荷转移激子引起的强双光子吸收。响应时间在时间分辨率范围内。

Ultrafast relaxation dynamics of quasi-one-dimensional halogen-bridged mixed-valence complexes (MX-compounds) has been investigated by the femto-second transient absorption measurements. In Pt-compounds, generation of vibrational excited states of self-traped excitons (STE's) and those of polarons and their relaxation processes to the meta-stable satates have been observed. On the other hand, it was found that the neutral solitons are generated within the time resolution (150fs). It is considered to be due to the dissipative nature of the potential surfaces. It was found that the time constants of the relaxation to the meta-stable states of STE's and the decay of times meta-stable STE's become shorter as the halogen ions were replaced in the order Cl, Br, and I in Pt-complexes. The generation efficiency of polarons has bee found to increases in the same order. These results are considered to be due to the increment of transfer energy and to the decrement of electron-phonon interaction. The generation efficiency of vibrational excited states of polarons was found to increase when the platinum ions were replaced by palladium ions. This is considered to be due to the increment of electron correlation.Vibrations of wave packet motion of photo-generated polarons and those of STE's in the potential surfaces around the meta-stable states have been found in a Pt-I-compound.Intense two-photon absorption caused by charge transfer excitons with odd parity has been found in MX-compounds. The response time was found to be within the time resolution.