Multi-Exciton Dynamics in Molecular Nano-Hybrid Systems

揭示分子系统中能量传递过程的细节一直是人们感兴趣的问题。光伏电池或发光二极管中电子激发能量转移的技术重要性是这种趋势的一个原因。另一个原因是多激子的产生、激子的裂变和融合以及与金属纳米结构或微腔光子的等离子体激子的杂化态的形成。为了探索这种新现象，不同分子同时被激发的较强光激发这一特殊区域将成为理论研究的重点。因此，我们将利用并进一步发展多电子理论来研究单个分子或分子二聚体的光诱导响应。应采用不同的基于波函数的方法。对于较大的分子络合物，将引入多激子方法，并推导出非线性动力学方程。在此基础上，应研究激发能量转移的超快光致过程，其中较高激发态的分子电子态变得密集(主要是在perylen或对二甲基苯基分子体系中)。对大量的非线性和部分相干的能量传递过程，特别是对光激发强度和持续时间的依赖，以及超越标准激子-激子湮没机制的描述，应该得到微观的描述。对于分子二聚体，多电子方法中的基准计算被用来验证多激子描述对同一系统所获得的结果的重要性。在此基础上，给出了多激子理论所需的能量和耦合矩阵元。为了弥合动力学方程的正式推导和光谱实验之间的差距，我们将计算发射光谱和瞬时吸收光谱。除了对孤立的分子络合物的研究外，我们还将考虑放置在分子附近的金属纳米粒子的等离子体激发的影响。应演示对多激子动力学的特殊控制。进入一个新的研究领域的一步将是考虑放置在微腔中的分子系统。根据文献的建议，我们将研究腔光子辅助激发分子间能量转移的新机制的形成。

It is of ongoing interest to uncover details of energy transfer processes in molecular systems. The technological importance of electronic excitation energy transfer in photovoltaic cells or light emitting diodes represents one reason for this tendency. Novel phenomena like multiple exciton generation, exciton fission and fusion as well as hybrid state formation with plasmon excitations of metal nano-structures or microcavity photons constitutes another reason. In order to explore such novel phenomena the particular regime of stronger optical excitation where different molecules are excited simultaneously will be in the focus of theoretical project work.Therefore, we will utilize and further develop a many-electron theory to study the photoinduced response of a single molecule or a molecular dimer. Different wave function based methods shall be applied. Turning to larger molecular complexes a multi-exciton approach will be introduced and nonlinear kinetic equations will be derived. With that ultrafast photoinduced processes of excitation energy transfer shall be studied where higher excited molecular electronic states become populated (mainly in systems of perylen or para-sexiphenyl molecules). A microscopic description of a multitude of nonlinear and partially coherent energy transfer processes shall be achieved, in particular in their dependence on intensity and duration of optical excitation and beyond the regime of standard exciton-exciton annihilation. Concerning the molecular dimer the benchmark computations within the many-electron approach are used to validate the importance of those results obtained with the multi-exciton description for the same system. Further-on, energies and coupling matrix elements needed for the multi-exciton theory are offered. To bridge the gap between the formal derivation of kinetic equations and spectroscopic experiments we will calculate, for example, emission and transient absorption spectra.Besides the study of isolated molecular complexes we will also account for effects of plasmon excitations of metal nano-particles placed in the vicinity of the molecules. A particular control of the multi-exciton dynamics shall be demonstrated. A step into a novel research area will be the consideration of molecular systems placed in a microcavity. Following suggestions from literature we will investigate the formation of new regimes of cavity photon assisted excitation energy transfer among the molecules.