Molecular-Level Approaches to Photosensitive Nanostructured Materials: A Combined Theoretical and Experimental Study of Ultrafast Energy and Charge Transfer

本项目关注的是基于苝二亚胺（PDI）的供体-受体（DA）嵌段共聚物形成高度有序的层状中间相的光诱导电荷产生的分子水平研究，这在有机光伏发电中具有应用前景。这些数据分析系统代表了最新一代的新一类材料，在该项目的初始资助期内，在与斯特拉斯堡大学S. Haacke小组联合DFG/ANR项目的框架内，对这些材料进行了光谱和理论研究。值得注意的是，在这些先前的研究中表明：(i)第一代材料表现出超快的电荷分离，但高的重组率，这可以用特定的分子包装特性来解释；（ii）第二代材料可以进行化学调谐，例如获得寿命长达几纳秒的电荷转移态，并且在溶液中重组率低。在此背景下，目前的后续项目致力于以高度有序的薄膜形态对第二代材料进行详细建模。基于现有的结构数据以及目前正在进行的新的时间分辨光谱研究，我们将结合电子结构和微静电计算、量子动力学计算、分子动力学模拟和动力学蒙特卡罗（KMC）模拟来获得从初始电荷分离到远程载流子输运的过程的详细图像。一个第一性原理的参数化晶格哈密顿量将使用电子结构计算的信息来构建合适的碎片，以及精确描述包括极化效应在内的局部静电的微静电处理。这种晶格哈密顿量为量子动力学模拟（在飞秒到皮秒尺度上）和KMC模拟（在皮秒到微秒尺度上）提供了统一的表示，并允许在多尺度设置中一致地嵌入动力学建模。在这种情况下，使用多层多构型时间相关哈特里（ML-MCTDH）方法的高维量子动力学计算将通常对超过一百种电子状态和振动模式进行，以覆盖长达数十皮秒的时间尺度。特别的重点将放在分子包装的作用，诱导激子和电荷离域，以及额外的转移途径。特别是，PDI堆叠有望导致电荷分离物质的复杂光化学反应，这可能会切实影响电荷的产生和传输。目前的分析有望量化化学成分和分子包装的综合影响，为下一代DA材料的合理设计提供必要的成分。

This project is concerned with the molecular-level investigation of photoinduced charge generation in perylene diimide (PDI)-based donor-acceptor (DA) block co-oligomer species forming highly ordered lamellar mesophases, which show promise for applications in organic photovoltaics. These DA systems represent the most recent generation of a new class of materials which have been spectroscopically and theoretically investigated during the initial funding period of this project, in the framework of a joint DFG/ANR project with the group of S. Haacke at Strasbourg University. Notably, it was shown in these previous investigations that (i) the first-generation materials show ultrafast charge separation but high recombination rates, which could be explained by the specific molecular packing properties, (ii) the second-generation materials can be chemically tuned, such as to obtain charge transfer states with lifetimes up to a few nanoseconds, and low recombination rates in solution. Against this background, the present follow-up project is devoted to the detailed modeling of the second-generation materials in a highly ordered thin-film morphology. Based upon available structural data as well as new time-resolved spectroscopic studies that are currently underway, we will use a combination of electronic structure and microelectrostatics calculations, quantum dynamical calculations, molecular dynamics simulations, and Kinetic Monte Carlo (KMC) simulations to obtain a detailed picture of the process, from the initial charge separation to long-range carrier transport. A first-principles parametrized lattice Hamiltonian will be constructed using information from electronic structure calculations for suitable fragments, along with a microelectrostatics treatment that accurately describes the local electrostatics including polarization effects. This lattice Hamiltonian provides a unified representation for both quantum dynamical simulations (on the femtosecond to picosecond scale) and KMC simulations (on the picosecond to microsecond scale), and permits a consistent embedding of the dynamical modelling in a multi-scale setting. In this context, high-dimensional quantum dynamical calculations using the Multi-Layer Multiconfiguration Time-Dependent Hartree (ML-MCTDH) method will be typically carried out for more than one hundred electronic states and vibrational modes, to cover a time scale up to tens of picoseconds. A special focus will be placed upon the role of molecular packing, inducing exciton and charge delocalization, along with additional transfer pathways. In particular, PDI stacking is expected to lead to a complex photochemistry of charge separated species, which could tangibly influence the charge generation and transport. The present analysis is expected to quantify the combined effects of chemical composition and molecular packing, providing essential ingredients for the rational design of next-generation DA materials.