Excited-State Properties of Multiply-Excited Oligonuclear Coordination Compounds

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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)?