LAUE TIME-RESOLVED DIFFRACTION OF MOLECULAR EXCITED STATES

这个子项目是利用资源的许多研究子项目之一。 由NIH/NCRR资助的中心拨款提供。对子项目的主要支持 子项目的首席调查员可能是由其他来源提供的， 包括美国国立卫生研究院的其他来源。为子项目列出的总成本可能 表示该子项目使用的中心基础设施的估计数量， 不是由NCRR赠款提供给次级项目或次级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 使用单脉冲和多脉冲劳厄衍射的光晶学时间分辨实验需要光束时间。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精确度。我们正在使用斑点积分的‘种子偏度’方法(Bolotovsky&Coppens J.Appl.克赖斯特。30244-253 1997)，它与剖面无关，很好地适应了时间分辨劳厄实验中100ps-1ms延迟范围内不同时间点观测到的剖面变化。我们正在与Tim Graber合作分析单脉冲强度的不稳定性，Graber在最近的测试实验中确定了波动的几个来源。 了解分子在激发时的几何变化及其与生色团寿命和底物吸附的关系，对于设计用于光捕获的分子器件是至关重要的。在光伏电池中，敏化剂-染料分子被吸附在半导体表面，半导体表面通常由二氧化钛的锐钛矿相组成。拟议的工作涉及二氧化钛纳米团簇的晶相，它再现了锐钛矿相的表面特征。这些材料中纳米团簇的周期性排列使X射线衍射可以详细地确定吸附分子的基态几何形状，并使用皮秒的超快时间分辨泵浦-探测衍射方法--分辨率确定在光激发下吸附剂和衬底的几何变化。结构结果将与光谱测量和理论计算相关联，以获得对由于光暴露而在分子涂层半导体表面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净晶体中分子的初始化学反应阶段以及嵌入骨架超分子固体中的分子的化学反应。感兴趣的反应包括异构化反应，如引发光活性黄蛋白二聚反应的反式顺式异构化反应和闭环反应。虽然可以用常规设备和激光激发来研究这类反应的相对缓慢的进展，但初始阶段，特别是短寿命过渡态和其他中间体的性质，需要使用脉冲X射线和光源的泵浦-探测技术。这项工作得到了能源部(第一部分)和国家科学基金会(第二部分)的资助。

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).