Ultrafast Dynamics of Electronic Excitations in Single Conjugated Polymer Chains

在基于p共轭聚合物的有机光伏器件中，电子激发的超快输运动力学是太阳能转换初始阶段的关键过程。然而，这类材料的电子结构，特别是电子激发的超快（亚皮秒）形成和输运动力学仍然不完全清楚和有争议的讨论。虽然这些过程原则上可以用传统的超快系综光谱进行研究，但共轭聚合物的结构和电子非均质性阻碍了对其详细理解的发展。因此，在这个项目中，我们将采用超快单分子光谱在分子尺度上研究一个原型和技术上重要的系统，低聚和多噻吩的性质。我们的目标是通过测量噻吩链长度、局部环境和温度的函数来解决基本电子激发的飞秒形成以及它们在单个噻吩链内的后续传输动力学。我们想要检索的时间尺度，弛豫能，和弛豫路径的电子激发在其初始形成和定位。此外，我们将研究影响链内能量传递的各种因素，如精确的链构象、电子相互作用以及局部链环境的作用和耦合。一个特别的重点将是在超短（< 250 fs）时间尺度上解决潜在的相干输运，并确定影响相干寿命的相关参数。

The ultrafast transport dynamics of electronic excitations is a key process in the initial steps of solar energy conversion in organic photovoltaic devices based on p-conjugated polymers. However, the electronic structure of this material class, and in particular the ultrafast (sub-picosecond) formation and transport dynamics of electronic excitations is still not entirely clear and controversially discussed. Although these processes can in principle be investigated by conventional ultrafast ensemble spectroscopy, the development of a detailed understanding is hampered by the large structural and electronic heterogeneity of conjugated polymers. In this project we will therefore employ ultrafast single-molecule spectroscopy to study the properties of a prototypical and technologically important system, oligo- and polythiophenes, on a molecular scale. We aim at resolving the femtosecond formation of fundamental electronic excitations as well as their subsequent transport dynamics within single thiophene chains by measurements as a function of the thiophene chain length, their local environment, and the temperature. We want to retrieve the time scales, the relaxation energies, and the relaxation pathways of electronic excitations during their initial formation and localisation. Moreover, we will investigate the various factors that influence the intra-chain energy transport, such as the precise chain conformation, the electronic interactions, as well as the role of and the coupling to the local chain environment. A particular focus will be to resolve potential coherent transport on ultrashort (< 250 fs) time scales and to identify the relevant parameters that impact on the coherence lifetime.