Understanding and Controlling Molecular Orientation in Organic Guest-Host Systems

有机半导体广泛应用于光电子器件，尤其是有机发光二极管(OLED)。尽管这些薄膜结构具有非晶态性质，但由于分子相对于衬底法线的取向顺序，它们的光学和(Di)电学性质会表现出显著的各向异性。通过这项更新建议，我们计划在几个方面扩大科学焦点，目标是更深入地了解有机客体-宿主系统中分子取向的驱动力。最重要的是，我们将通过将我们的工作计划组织成两个互补但同样重要的实验部分来关联光学和电偶极矩，这些实验部分将在U Augsburg的Bruting小组进行。此外，温泽尔团队在KIT的第三个工作包将通过分子模拟来解决这些问题。通过这种整体的方法，我们期望对层的形态有详细的了解，并对机械理解有重要的附加值。此外，对于发射体材料的分类，我们将主要关注热激活延迟荧光(TADF)发射体，即具有激发态电荷转移(CT)特性的供体-受体体系。一方面，由于它们广泛的分子结构，人们可以预期在薄膜中有很强的取向效应，另一方面，由于它们的CT特性，我们预计会有很强的客体相互作用，特别是与极性主体材料的相互作用。最后，我们计划大幅扩展我们的实验能力，以测量时间分辨技术的发射器方向。这对于TADF发射器来说尤其有趣，因为它们的即时和延迟荧光在几个数量级的时间内起作用。根据时间尺度的不同，发射可能来自发射体分子上的不同电子态，并且通常来自具有不同局部环境的染料分子。

Organic semiconductors are nowadays frequently used in optoelectronic devices, particularly in organic light emitting diodes (OLEDs). In spite of their amorphous nature, these thin film structures can exhibit a pronounced anisotropy of their optical and (di)electric properties, resulting from orientational order of the molecules with respect to the substrate normal. With this renewal proposal we plan to broaden the scientific focus in several aspects with the goal to achieve a deeper understanding of the driving forces for molecular orientation in organic guest-host systems. Most importantly, we will correlate optical and electrical dipole moments by structuring our work program into two complementary, but equally important experimental parts to be conducted in the Bruetting group at U Augsburg. Additionally, a third work package by the Wenzel group at KIT will address these topics by molecular simulation. From this holistic approach, we expect detailed insights into the layer morphology and significant added value into the mechanistic understanding. Moreover, regarding the class of emitter materials, we will mainly focus on thermally acitvated delayed fluorescence (TADF) emitters, i.e. donor-acceptor systems with charge-transfer (CT) character in the excited state. On the one hand, owing to their extended molecular structures, one can expect strong alignment effects in thin films, and on the other hand, due to their CT character we anticipate strong guest-host interactions, specifically with polar host materials. Finally, we plan a substantial extension of our experimental capabilities for measuring emitter orientation towards time-resolved techniques. This is particularly interesting for TADF emitters with their prompt and delayed fluorescence acting over several orders of magnitude in time. Depending on the time scale, the emission can originate from different electronic states on the emitter molecule and often stems from dye molecules with different local environments.