Ultrafast Dynamics of Electronic Excitations in Single Conjugated Polymer Chains

电子激发的超快输运动力学是基于p-共轭聚合物的有机光伏器件中太阳能转换初期的关键过程。然而，这类物质的电子结构，特别是电子激发的超快(亚皮秒)形成和输运动力学仍然不是完全清楚的和有争议的讨论。虽然这些过程原则上可以用传统的超快系综光谱来研究，但共轭聚合物的结构和电子的巨大异质性阻碍了对这些过程的详细理解。因此，在这个项目中，我们将使用超快的单分子光谱学在分子尺度上研究一个具有重要技术意义的原型体系--低聚噻吩类化合物的性质。我们的目标是通过测量作为噻吩链长度、局域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随后在单噻吩链中的输运动力学。我们想要恢复电子激发在其初始形成和局域化过程中的时间标度、弛豫能和弛豫路径。此外，我们还将研究影响链内能量传输的各种因素，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解决超短(&lt；250 fS)时间尺度上的潜在相干传输，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.