Photoinduced macroscopic polarization change with long-lived metastable state

本研究的目的是实现光诱导激发自旋态俘获效应(LIESST)在自旋交叉晶体中实现的光致持久极化变化。在第一年我们得到了具有光致极化变化的Fe(II)自旋跃迁络合物之后，我们主要集中在探索引起极化变化的因素。考虑到辐照后结构转化率低，激发态的结构难以分析，我们通过变温穆斯堡尔谱证实，辐照前后有24%的Fe(II)从基态的低自旋态转变为激发态的高自旋态。此外，变温红外光谱也为这一结果提供了证据。通过变温单结构分析确定了从273K到393K的自旋转变的结构数据。结合点电荷计算和理论计算，计算结果表明，大的极化变化源于离子的偏心位移，离子的收缩或膨胀是由于自旋跃迁引起的。研究还表明，在极性晶体中实现了光致离子运动。为了改进这项工作，开发了另一种表现出光致极化变化和完全自旋跃迁的自旋交叉络合物。这是研究光诱导极化变化的机理，进而改善极化变化的较好模型。

The purpose of this research project is to realize the photoinduced persistent polarization change in spin crossover crystals attained by Light-Induced Excited Spin-State Trapping (LIESST) effect. After we obtained a Fe(II) spin transition complex with photoinduced polarization change in the first year, we mainly focused on exploring the factors induced the polarization change. Considering the structure of the excited state is difficult to analysis due to the low structural conversion ratio after irradiation, we confirmed that 24% of Fe(II) changes from the low spin state of the ground state to the high spin state of the excited state through variable temperature Mossbauer spectra before and after irradiation. In addition, the variable temperature IR spectra have also afforded the evidence for this result. The structure data during the spin transition from 273 K to 393 K were determined by the variable temperature single structure analysis. Combined the point charge calculation and the theoretic calculation, the calculated result indicates that the large polarization change originates from the off-centering ion displacement because of the shrinkage or expansion of cations due to the spin transition. It also shows that light-induced ion movement in a polar crystal is realized. To improve this work, the other spin crossover complex that exhibited photoinduced polarization change and complete spin transition was developed. It is a better model to study the mechanism of photoinduced polarization change and then to improve the polarization change.