Excited-State Properties of Multiply-Excited Oligonuclear Coordination Compounds

来自合成和物理化学的两个小组提出的联合项目旨在研究包含Ru(II), Fe(II), Os（II）和Cr（III）的三核和寡核配合物的超快激发态过程，其中心是金属到配体电荷转移的激发。目前对三核和寡核配合物在低强度激发下的激发态弛豫动力学研究较多。然而，在本研究中，将采用高激发强度的制度。这是第一次对这一体系进行系统研究，以获得详细的结构-动力学关系。该项目将解决与多激发态寡核复合物的激发态特性相关的核心问题，例如，如果从共轭聚合物的光物理学中已知的激子-激子湮灭的概念也可以转化为分子配位化合物，以及如何通过复杂的设计来调整其动力学。此外，动力学阻碍分子内能量转移的细节将被利用-一个过程最近报道的过程在一个示范性的三核供体-受体-供体系统。该项目的主要主题是关于光诱导多电子过程的发展以及对三核和寡核金属配合物中激发态的理解和设计。在联合初步工作的继续，混合金属配合物与-共轭双双吡啶配体将被用作构建模块，并研究了一些机制方面：分子设计对单个分子组装中两个不同金属中心光激发的三重态-三重态激发态湮灭的影响有多大？能否利用分子设计来操纵三核供体-受体-供体复合物中动力学阻碍的分子内能量转移速率？如果扩展配合物中供体单位的数量增加（考虑到不止一个供体位点被激活），上述过程将如何受到影响？

The proposed joint project between two groups from synthetic and physical chemistry targets the investigation of ultrafast excited-state processes in tri- and oligonuclear complexes incorporating Ru(II), Fe(II), Os(II) and Cr(III) centers upon excitation of the metal-to-ligand charge-transfer. Up to now mainly the excited-state relaxation dynamics of tri- and oligonuclear complexes under low-intensity excitation have been reported. In this study, however, the regime of high-excitation intensities will be employed. For the first time, a systematic study in this regime will be performed to derive detailed structure-dynamics relationships. The project will address central questions associated with the excited-state properties of multiply excited oligonuclear complexes, e.g., if the concept of exciton-exciton annihilation, as known from the photophysics of conjugated polymers, can also be translated to molecular coordination compounds and how its kinetics can be tuned by complex design. Moreover, the details of kinetically hindered intramolecular energy transfer will be exploited – a process recently reported process in an exemplary trinuclear donor-acceptor-donor system. The main theme of the proposed project is related to the development of photoinduced multi-electron processes and the understanding as well as the design of excited states in tri- and oligonuclear metal complexes. In continuation of the joint preliminary work, mixed-metal complexes with -conjugated bisterpyridine ligands will be employed as building blocks and investigated regarding a number of mechanistic aspects: How far does the molecular design effect the triplet-triplet excited-state annihilation upon photoexcitation of two distinct metal centers within a single molecular assembly? Can the molecular design be utilized to manipulate the rate of kinetically hindered intramolecular energy transfer within trinuclear donor-acceptor-donor complexes? How are the aforementioned processes affected if the number of donor units within the extended complexes is increased (given that more than a single donor site is excitated)?