LAUE TIME-RESOLVED DIFFRACTION OF MOLECULAR EXCITED STATES

分子激发态的劳尔时间分辨衍射

• 批准号: 8363703
• 负责人: PHILIP COPPENS
• 金额: $ 5.47万
• 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/8363703
• 关键词: Adsorption; Cells; Characteristics; Collaborations; Devices; Dimerization; Dyes; Equipment; Funding; Goals; Grant; Knowledge; Lasers; Life; Light; Measurement; Methods; Molecular; National Center for Research Resources; Nature; Optics; Phase; Physiologic pulse; Principal Investigator; Process; Pump; Reaction; Research; Research Infrastructure; Resolution; Resources; Roentgen Rays; Seeds; Semiconductors; Solid; Source; Spottings; Staging; Surface; Techniques; Testing; Time; United States National Institutes of Health; Work; X ray diffraction analysis; X-Ray Diffraction; anatase titanium dioxide; chemical reaction; chromophore; cis trans isomerization; cost; data reduction; design; interest; research study; structural biology; titanium dioxide

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. Time-resolved Studies of Molecular Excited States and Chemical Reactions Beamtime is requested for photocrystallographic time-resolved experiments using single- and multi-pulse Laue diffraction. As part of the project experimental and data-reduction methods are being revised to maximize the accuracy of the Laue intensities and the optical resolution. We are using the 'seed-skewness' method of spot integration (Bolotovsky & Coppens J. Appl. Cryst. 30 244-253 1997)which is profile-independent and well suited for the profile changes observed at different time point in the 100ps-1 ms delay range in time-resolved Laue experiment. We are analyzing instabilities in the single-pulse intensities in collaboration with Tim Graber who has identified several sources of the fluctuations in very recent test experiments. Knowledge of the geometry changes of molecules on excitation and their relation to lifetimes and adsorption of chromophores on substrates is of crucial importance for the design of molecular devices used in light capture. In photovoltaic cells sensitizer-dye molecules are adsorbed on a semiconductor surface which is typically composed of the anatase phase of titanium dioxide. The proposed work involves crystalline phases of titanium dioxide nanoclusters which reproduce the surface characteristics of the anatase phase. The periodic arrangement of the nanoclusters in these materials allows detailed X-ray diffraction determination of the geometry of the adsorbed molecules in their ground state and by use of ultrafast time-resolved pump-probe diffraction methods at picoseconds-resolution determination of the geometry changes of both the adsorbent and the substrate on excitation by light. The structural results are to be correlated with spectroscopic measurements and theoretical calculations to obtain atomic-resolution understanding of the processes that take place on molecule-coated semiconductor surfaces as a result of light exposure. A second goal of the project is the study of initial stages of chemical reactions of molecules in neat crystals as well as of of molecules embedded in framework supramolecular solids. Reactions of interest include isomerizations such as the trans-cis isomerization triggering the reaction of photoactive yellow protein dimerization and ring closure reactions. Whereas the relatively slow progress of such reactions can be studied with conventional equipment and laser excitation the initial stages and in particular the nature of short-lived transition states and other intermediates requires pump-probe techniques with pulsed X-ray and light sources. The work is funded by DOE (first part) and by NSF (second part).

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， 包括其他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。 分子激发态和化学反应的时间分辨研究 光束时间要求使用单脉冲和多脉冲劳厄衍射的光晶体时间分辨实验。 作为该项目的一部分，正在修订实验和数据简化方法，以最大限度地提高劳厄强度和光学分辨率的准确性。 我们使用的“种子偏度”的斑点积分方法（Bolotovsky & Coppens J.Appl.Cryst.30 244-253 1997），这是轮廓独立的，非常适合于在不同的时间点观察到的轮廓变化在100 ps-1 ms的延迟范围内的时间分辨劳厄实验。 我们正在与Tim Graber合作分析单脉冲强度的不稳定性，Tim Graber在最近的测试实验中确定了几个波动源。 激发时分子的几何形状变化及其与生色团在底物上的寿命和吸附的关系的知识对于用于光捕获的分子器件的设计是至关重要的。 在光伏电池中，敏化剂-染料分子被吸附在半导体表面上，该半导体表面通常由二氧化钛的双相组成。 拟议的工作涉及二氧化钛纳米团簇的结晶相，其再现了纳米相的表面特性。在这些材料中的纳米团簇的周期性排列允许详细的X射线衍射确定的几何形状的吸附分子在其基态和通过使用超快的时间分辨的泵浦-探测衍射方法在皮秒分辨率确定的几何形状变化的吸附剂和基板上的光激发。 结构结果与光谱测量和理论计算相关，以获得对分子涂覆的半导体表面由于曝光而发生的过程的原子分辨率理解。 该项目的第二个目标是研究纯晶体中分子的化学反应的初始阶段以及嵌入框架超分子固体中的分子。感兴趣的反应包括异构化，例如引发光活性黄色蛋白二聚化反应和闭环反应的反式-顺式异构化。 虽然这种反应的相对缓慢的进展可以用常规设备和激光激发来研究，但初始阶段，特别是短寿命过渡态和其他中间体的性质，需要用脉冲X射线和光源的泵浦-探测技术。这项工作由DOE（第一部分）和NSF（第二部分）资助。