Excitonic states in spatially confined molecular structures

本项目旨在研究分子半导体晶体结构中的主要光激发及其动力学行为。作为一个关键问题，我们将分析空间受限的激发体积及其界面对激子态及其时间演化的影响。为此，将通过升华法制备多芳分子（如rubrene或苝衍生物）具有自组织外延表面结构的长程有序单层和块状单晶。之后，这些样品将进行结构和光学表征，后者通过微米横向分辨率的光致发光测量。激子态能量学的基本信息将通过它们的光谱表征得到，弛豫动力学和活化能将被推断为横向位置和温度在4 ~ 400k范围内的函数。在晶体层的情况下，我们将讨论表面体积比以及界面上的平移不变性对光激发的局域和离域的影响。应用具有不同性能的封井层提供了额外的自由度，可以以可控和可靠的方式改变结构和电子界面特性，从而研究它们的影响。我们将注意光激发的能量位置以及弛豫通道随激发体积大小和界面状态的变化甚至抑制。将这些研究扩展到分子单晶顶部的微观表面结构将揭示有关现象的空间各向异性的深刻见解。通过完整的数据集，我们打算详细了解晶体分子堆栈中的光学激发态及其受几何边界条件的影响。在这些研究过程中，不仅将评估微观激子过程，如单线态激子裂变及其在光电器件概念中的应用，还将制备具有明确功能的创新结构。作为一个关键课题，将利用空间受限激发体积和定制边界的组合来将单个分子与局部场分布耦合起来。通过其改进的发射特性，我们将建立一种实现新功能的方法，这些功能对于实现非经典单光子源至关重要。为了实现所描述的目标，由各种合作伙伴组成的协调一致的方法，包括在合成、超快光谱和理论建模方面的专业知识是不可避免的。应用研究单元FOR1809满足并保证了所有这些要求。

This project aims for investigation of the primary optical excitations and their dynamic behavior in crystalline structures made of molecular semiconductors. As a key issue we will analyze the influence of spatially confined excitation volumes and their interfaces on the excitonic states and their temporal evolution. For this purpose, long-range ordered monolayers as well as bulk single crystals with self-organized, epitaxial surface structures will be prepared of polyaromatic molecules, such as rubrene or perylene-derivatives, via sublimation. Thereafter, these samples will be structurally and optically characterized, the latter by photoluminescence measurements at micrometer lateral resolution. The essential information on the energetics of the excitonic states will be obtained by their spectral characterization and the relaxation dynamics as well as activation energies will be deduced as a function of lateral position and temperature in a range between 4 and 400 K. In case of crystalline layers we will address questions on the impact of the surface-tovolume-ratio as well as of the translational invariance at the interfaces on the localization and delocalization of optical excitations. Applying capping layers with different properties provides an additional degree of freedom to vary the structural and electronic interface characteristics in a controlled and reliable fashion and thus to study their influence. We will draw our attention on the energy position of optical excitations and the variation or even suppression of relaxation channels by the size of the excitation volume as well as by interfacial states. Extending those studies to microscopic surface structures on-top of molecular single crystals will reveal profound insights in the spatial anisotropy of the related phenomena. By means of the entire sets of data we intend to develop a detailed understanding of the optically excited states in crystalline molecular stacks and of their influence by geometrical boundary conditions. In the course of these studies not only the microscopic excitonic processes, such as singlet exciton fission, and their utilization in optoelectronic device concepts will be evaluated but also innovative structures with defined functionalities will be prepared. As a key topic, the combination of spatially confined excitation volumes and tailored boundaries will be utilized to couple single molecules to the local field distribution. By their modified emission characteristics we will establish an approach towards new functionalities, which are essential e.g. for the implementation of non-classical, single photon sources. To achieve the described objectives, a concerted approach by various partners comprising expertise on the subject of synthesis, ultrafast spectroscopy and theoretical modelling is inevitable. All these requirements are fulfilled and guaranteed by the applied research unit FOR1809.