Experimental and Theoretical Studies towards the Charge Recombination of Organic Radicals in Inorganic Mesostructures

两个氧化还原中心之间的光诱导电荷分离是电子转移过程的基本步骤之一。为此，研究电荷分离和重组的模型过程，例如以大的多环芳烃（PAH）作为探针分子，其稳定的自由基中心已被充分记录，可能使人们对光转化为化学上可用的功、DG和电荷重组的动力学有基本的了解。在多环芳烃探针分子氧化还原中心（如二溴二烯或季二烯）相互靠近的分子间，定义良好的分隔反应空间允许在几何约束条件下研究基本电荷重组过程。重组参数取决于给定宿主空间的大小以及所研究的无机自由基的个体取向。作为宿主，将使用一维纳米和介孔无机氧化物，如氧化铝或MCM 41家族的介孔宿主，它们提供高度有序的平行孔排列，为大型多环芳烃的自由基形成和重组提供有限的反应空间。为了研究电荷分离种的命运，瞬态光谱测量是必要的。时间分辨激光光谱，将用于研究动力学的电荷重组通过光学和/或电导率检测。在这些实验中，激光的脉冲宽度控制着实验的时间分辨率。自旋密度和g值等自由基性质以及动态电荷交换现象是ESR-和ENDOR详细研究的主题。利用量子化学和分子模拟的理论研究将有助于理解微观情况和建立时间分辨光谱模型。该项目的这一部分旨在确定在各种条件下纳米和介孔沸石和铝型材料的模型表面吸附多环芳烃的结构和能量特征，模拟实验选择的几何约束的多孔氧化铝和MCM 41的反应空间。多环芳烃客体分子的平衡表面密度分布及其取向排序信息是预期的研究结果。最后，化学，几何（在利用多孔主体材料所代表的可变约束条件的意义上），以及基于微观洞察力的电荷传递动力学的热力学控制。

The photoinduced charge separation between two redox centers is one of the basic steps in electron transfer (ET) processes. For this purpose the study of model processes of charge separation and recombination, as exemplified with large polycyclic aromatic hydrocarbons (PAH) as probe molecules for which stable radical centers are well documented, might allow fundamental insights into the kinetics of light conversion into chemically usable work, DG, and for charge recombination. Well defined compartmented reaction spaces where PAH probe molecule redox centers like e.g. dicoronenylene or quaterylene are held in intermolecular proximity to each other allow to study fundamental charge recombination processes under geometrically constrained conditions. Recombination parameters are dependent on the size of the given host space as well as the individual orientation of the inorganic radicals under study. As hosts, one dimensional nano- and mesoporous inorganic oxides like alumina or mesoporous hosts of the MCM 41 family that offer a highly ordered parallel pore arrangement will be used, making available a constrained reaction space for radical formation and recombination of large PAHs. To study the fate of charge separated species transient spectroscopic measurements are necessary. Timeresolved laser spectroscopy, will be used to investigate the kinetics of charge recombination by optical and/or conductivity detection. Within these experiments employed pulse widths of the lasers control the time resolution of the experiments. Radical properties like spin densities and g values as well as dynamic charge exchange phenomena are subjects of detailed ESR- and ENDOR studies. Understanding the microscopic situation and modeling the time-resolved spectra will be facilitated by theoretical studies employing quantum chemistry and molecular simulations. That part of the project is aimed towards a determination of structural and energetic characteristics of PAH adsorption on model surfaces of nano- and mesoporous zeolite- and aluminatype materials under various conditions mimicking the experimentally chosen geometrically constrained reaction spaces of porous alumina and MCM 41. Equilibrium surface density distributions of PAH guest molecules along with information about their orientational ordering are expected research results. Ultimately, chemical, geometrical (in the sense of utilizing the variable confinement conditions represented by the porous host material), as well as thermodynamic control of charge transfer kinetics based on microscopic insight is aspired.