Carrier-relaxation dynamics in model crystalline organic semiconductors

本项目致力于研究单晶有机半导体的弛豫动力学。特别是，分子堆积模体和光电响应之间的关系将被探索。将在三个模型体系中研究它们的松弛机制，分别是茂、并五苯和全氟戊烯。这些典型的小分子都形成了各种晶型的高度有序的van.der-Waals键合单晶。一方面，随着对激发离域和分子间耦合等现象的研究，这具有重要的科学意义。另一方面，这些发现有望深入了解当前有机光电子器件的性能限制，并为优化结构和材料设计提供预测能力。在实验上，这些挑战将通过高空间分辨率的偏振分辨光学光谱来解决。基本的siglet和triplet类型的跃迁将通过调制的反射和透射谱进行识别，并与结果模型计算进行比较。具体地说，在静态外部磁场中，三重态基态将变得可光学寻址。此外，发射光谱将被用来证实这些发现。时间分辨测量有助于区分直接间隙过渡和间接间隙过渡。我们将特别关注单重态激子裂变的微观机制，即一个单重态激子转变为两个三重态。并探讨了选择性系统间杂交的效率。此外，我将探索增强的近邻耦合的作用，例如，导致准分子的形成。以及通过形成这种相关的分子对激发态而引起的晶格的相关扭曲。因此，单个分子将通过全氟化或氢化有选择地改变。

This project is devoted to studying the relaxation dynamics in single-crystalline organic semiconductors. In particular, the relation between the molecular packing motifs and the optoelectronic response will be explored. The relaxation mechanism will be studied in three model systems perylene, pentacene, and perfluoropentacene. These prototypical small molecules all form various polymorphs of highly-ordered van.-der-Waals-bonded single crystals. On the one hand, this is of fundamental scientific interest as phenome such as delocalization of excitations and intermolecular coupling are explored. On the other hand the findings are expected to yield insights in the performance limitations of current organic optoelectronic devices as well as provide predictive capabilities towards optimized structure and materials design. Experimentally, these challenges will be addressed by polarization-resolved optical spectroscopy with high spatial resolution. The fundamental siglet and triplet-type transitions will be identified by modulated reflection and transmission spectroscopy and compared to results model calculations. In particular, the triplets ground states will become optically addressable in static external magnetic fields. Furthermore, emission spectra will be used to corroborate these findings. Time-resolve measurements help to distinguish direct-gap from indirect-gap transitions. A particular focus will be put on the microscopic mechanism of singlet-exciton fission, the conversion of one singlet-type exciton into two triplet states. And explore the efficiency of selective intersystem crossing. Furthermore, I will explore the role of enhanced next-neighbour coupling resulting in, e.g., excimer formation. And the related distortion of the crystalline lattice through the formation of this correlated molecule-pair excited state. Therefore, the individual molecules will be selectively changes by perfluorination or deuteration.