LAUE TIME-RESOLVED DIFFRACTION OF MOLECULAR EXCITED STATES

该子项目是利用 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得主要资金， 因此可以在其他CRISP条目中表示。列出的机构是 中心，不一定是研究者的机构。 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，很好地适用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，其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，并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。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. 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.