TIME-RESOLVED X-RAY DIFFRACTION STUDIES OF PHOTOINDUCED SPIN TRANSITION IN M

M 光致自旋跃迁的时间分辨 X 射线衍射研究

• 批准号: 8363676
• 负责人: ERIC COLLET
• 金额: $ 7.1万
• 依托单位: UNIVERSITY OF CHICAGO
• 依托单位国家: 美国
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-08-01 至 2012-07-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8363676
• 关键词: Complex; Data Collection; Dependence; Dependency; Electronics; Electrons; Equilibrium; Foundations; Freedom; Freezing; Funding; Grant; Heating; Investigation; Kinetics; Lasers; Ligands; Magnetism; Molecular; National Center for Research Resources; Nature; Optics; Pathway interactions; Principal Investigator; Process; Property; Research; Research Infrastructure; Resources; Solid; Source; Structure; System; Temperature; Time; United States National Institutes of Health; Variant; X ray diffraction analysis; X-Ray Diffraction; cost; interest; nanosecond; photo switch; solid state; structural biology

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. We propose to investigate the out-of-equilibrium switching dynamics during the photoinduced spin conversion from low-spin (LS) to high-spin (HS) states in two different spin-crossover solids (weakly and highly cooperative crystals respectively). The photo-switching is triggered by a femtosecond laser flash. Preliminary time-resolved x-ray diffraction and optical studies on a weakly cooperative system have shown that the dynamics span from sub-picosecond local photo-switching followed by volume expansion (nanosecond) and thermal switching (microsecond). We want to perform a detailed analysis of this multi-scale switching process in particular by - checking the temperature dependence of photoinduced spin-crossover in [(TPA)Fe(III)(TCC)]PF6 and it's derivative observed to be maximum around the crossover temperature: the thermal microsecond switching should be strongly dependent of temperature with a maximum around the thermal equilibrium crossover temperature T1/2 whereas the sub-ps non-thermal switching should not shown such a dependency. - investigating the (Fe(phen)2NCS2) crystal which reveal cooperatif effects such as thermal hysteresis loop in which elastic interactions are expected to enhace the conversion of molecules from low-spin to high-spin states. In this case elastic interactions may increase the converted fraction of molecules from low-spin to high-spin statesespecialy on the ns time-scale where volume expansion takes place. Time-resolved x-ray diffraction makes it possible to track the structural signatures of this photoswitching process for a better understanding of the multi-scale out-of-equilibrium dynamics. As the spin-crossover molecules switch from low spin to high spin states leading to a change in magnetic and optical properties the electronic redistribution of the electrons on the d orbitals induces a large variation (0.2 A) of the Fe-ligand bonds. For obtaining this structural information complete data collections for solving and refining the corresponding structures are necessary. We propose to investigate the complete time course of the out-of-equilibrium dynamics from 100 ps to 1 ms. By solving the average cristallographic structures at any delay we will track not only the intra-molecular reorganization but also inter-molecular changes volume expansion as well as heating propagation through Debye-Waller factors in particular. Such investigations are of fundamental interest for a better understanding of the photoinduced molecular switching in the solid state. The structural information is crucial for establishing the physical foundations on how to direct macroscopic photo-switching in materials. A key feature is that dynamics follows a complex pathway from molecular to material scales through a sequence of processes. Not only is the pathway indirect the nature of dynamical process along the pathway depends on time scale. This dictates which kind of degrees of freedom is involved in the subsequent dynamics or kinetics and which ones are frozen or statistically averaged. By comparing different compound we will have a better understanding of what is universal in these processes.

这个子项目是许多利用资源的研究子项目之一 由NIH/NCRR资助的中心拨款提供。子项目的主要支持 而子项目的主要调查员可能是由其他来源提供的， 包括其它NIH来源。 列出的子项目总成本可能 代表子项目使用的中心基础设施的估计数量， 而不是由NCRR赠款提供给子项目或子项目工作人员的直接资金。 本文研究了两种不同自旋交叉固体（分别为弱合作晶体和高合作晶体）中光诱导自旋从低自旋（LS）态到高自旋（HS）态转变过程中的非平衡态转换动力学. 光开关由飞秒激光闪光触发。初步的时间分辨X射线衍射和光学研究弱合作系统的动态跨度从亚皮秒本地光开关，然后体积膨胀（纳秒）和热开关（微秒）。我们想对这种多尺度切换过程进行详细分析，特别是通过 - 检查在[（TPA）Fe（III）（TCC）] PF 6中的光诱导自旋交叉的温度依赖性，并且观察到其导数在交叉温度附近最大：热微秒切换应该强烈地依赖于温度，在热平衡交叉温度T1/2附近具有最大值，而亚ps非热切换不应该显示出这种依赖性。 - 研究了（Fe（phen）_2NCS_2）晶体的协同效应，如热滞回线，其中弹性相互作用促进了分子从低自旋态向高自旋态的转变。在这种情况下，弹性相互作用可能会增加分子从低自旋到高自旋状态的转换分数，特别是在体积膨胀发生的ns时间尺度上。 时间分辨的X射线衍射使得有可能跟踪这种光开关过程的结构特征，以更好地理解多尺度的平衡动力学。 由于自旋交叉分子从低自旋切换到高自旋状态，导致磁性和光学性质的变化，d轨道上的电子的电子再分布引起Fe-配体键的大的变化（0.2 A）。为了获得这种结构信息，需要完整的数据收集来求解和细化相应的结构。我们建议调查从100 ps到1 ms的平衡动力学的完整的时间过程。通过解决在任何延迟的平均晶体结构，我们将跟踪不仅是分子内的重组，但也分子间的变化，体积膨胀，以及特别是通过德拜-沃勒因子的热传播。 这些研究对于更好地理解固态光诱导分子开关具有重要意义。结构信息对于建立如何指导材料中的宏观光开关的物理基础至关重要。一个关键的特征是，动力学遵循一个复杂的途径，从分子到材料尺度，通过一系列的过程。不仅路径是间接的，而且沿着路径的动力学过程的性质依赖于时间尺度。这决定了在随后的动力学或动力学中涉及哪种自由度，以及哪些自由度被冻结或统计平均。通过比较不同的化合物，我们将更好地了解这些过程中的普遍性。