Molecular and Electronic Structure in Thin Films of Semiconducting Polymers as Studied in the Infrared and UV/Vis Spectral Range

半导体聚合物结合了整洁聚合物的优点，如机械坚固和重量轻，与半导体的电子特性和低成本的大面积沉积的可能性，这提供了相当大的技术效益。尽管在有机电子学领域进行了深入的研究，有机发光二极管(OLED)也取得了商业上的成功，但许多非常基本的问题仍然没有得到解答。例如，在有序的有机半导体薄膜中，电荷和激子被认为是具有带状输运的高度有序的无机半导体和具有跳跃输运的非常无序的系统之间的中间体。然而，我们还不知道如何控制这种结构来提高电荷或激子的相干长度。这种缺乏了解的部分原因是缺乏合适的微结构探针，这些探针对纳米级的无序很敏感。在这个项目中，建议在莱比锡大学最近工作的基础上，使用红外跃迁矩取向分析(IR-TMOA)来探索有机半导体中亚分子结构的部分特定取向和有序性。这项技术到目前为止是独一无二的，而且只在莱比锡可用，它能够在与能量和电荷转移相关的长度尺度上建立结构和无序程度的全面图像。利用谢菲尔德大学的时间分辨光谱测量，IR-TMOA的微观结构发现将与激子和电荷转移相干长度的测量相关联。测量计划在模型聚合物P3HT及其新型瓶刷衍生品上进行检验。分子量和化学结构会改变结晶度和微观结构环境。此外，模型共聚物PNDIT2(或P(NDI2OD-T2))及其硫化衍生物2S-TRANS-PNDIT2可以研究化学取代对分子取向和有序性以及电荷转移和激子相干长度的影响。到目前为止，这种实验技术的组合还没有发表过，并有望对分子结构和电子性质的相互作用提供新的见解。除了使用时间分辨光谱和稳态IR-TMOA作为独立的方法外，还计划将TMOA的测量原理与时间分辨红外光谱相结合。这将首次导致一种测量技术，允许研究分子单元的取向和有序性的动力学。

Semiconducting polymers combine advantages of neat polymers, such as mechanical robustness and light weight, with semiconducting electronic characteristics and the possibility of low-cost large-area deposition, which provides considerable technological benefits. Despite the intensive research in the field of organic electronics and the commercial success of organic light emitting diodes (OLEDs), many very fundamental questions remain unanswered. For example, in well-ordered organic semiconductor films charges and excitons are thought to behave as intermediate between highly ordered inorganic semiconductors, with band-like transport, and very disordered systems with hopping transport. However, we do not yet understand how the structure can be controlled to improve charge or exciton coherence length. This lack of understanding is in part due to the lack of suitable microstructural probes that are sensitive to disorder on the nanometer scale. In this project, it is propose to build up upon recent work at Leipzig University using infrared transition moment orientational analysis (IR-TMOA) to probe the moiety-specific orientation and order of sub-molecular structures in organic semiconductors. This technique –so far unique and only available in Leipzig– enables to build up a comprehensive picture of the structure and the degree of disorder at the length scale relevant for energy and charge transfer. Using time-resolved spectroscopy measurements at the University of Sheffield, the microstructural findings from IR-TMOA will be correlated with measurements of the exciton and charge transfer coherence length. Measurements are planned to be examined at the model polymer P3HT and their novel bottlebrush derivatives. The degree of crystallinity and the microstructural environment will be altered by the molecular weight and chemical structure. Furthermore, the model co-polymer PNDIT2 (or P(NDI2OD-T2)) and its thionated derivative 2S-trans-PNDIT2 allows for studying the influence of chemical substitution and hence altered molecular orbital energy levels on the molecular orientation and order as well as charge transfer and exciton coherence length. So far this combination of experimental techniques has not been published previously and promises new insights into the interplay of molecular structure and electronic properties. In addition to the use of time-resolved spectroscopy and steady-state IR-TMOA as independent methods, it is planned to combine the measurement principle of TMOA with time-resolved infrared spectroscopy. This will lead for the first time to a measurement technique which allows for studying the dynamics of orientation and order of molecular units.