Daniel Marhöfer

• This thesis shows the capability of time-resolved spectroscopic methods in investigating the photophysical and photochemical processes involved in a plethora of applications. It also highlights the necessity of combining orthogonal spectroscopic techniques to get a complete understanding of the excited states involved. I performed step-scan FTIR spectroscopy, luminescence spectroscopy and time-correlated single photon counting on multiple series of mono- and oligometallic complexes and thereby identified trends, which can be used in further optimization of the photophysical behaviour of the investigated metalorganic compounds and similar complexes by modifications. The interpretation of the spectra with (TD)-DFT methods helped in distinguishing between similar species as for example with determining the structure of ligands and determining oxidation and spin states of both ground and excited states of not only the original complex, but also intermediate species and photoproducts. The influence of substitution patterns of ligands was investigated and a clear trend between electron donating and electron withdrawing substituents was found by step-scan spectroscopy, while it remained unclear in the photoluminescence measurements alone due to the strong effect of the sample matrix. The replacement of bystander ligands proved to assert severe effects on the lifetimes and TADF capabilities in a series of complexes, strongly suggesting a large involvement of the spin-orbit coupling in the excited states with ligands with elements with higher ordinal numbers. Cooperative effects by metallophilic interactions proved to play a vital role with some metal combinations forming strong intermetallic interactions in the ground and excited states, some in neither state and one other only in the excited state, leading to a structural deformation of the ligand backbone in the excited state geometry. The influence of constitutional isomers was investigated and showed to have stronger effects than originally expected not only increasing lifetimes of excited states, but also transforming dark states into luminescent ones. Finally, the influence of oxidation and spin states on vibrational spectra, especially on the stretching vibrations of hydrogen bonding was utilized to clarify the ground state structures of a series of trimetallic complexes while measurements previous to the investigations seemed to contradict each other. A variety of seemingly minor changes in metalorganic complexes was characterized leading to meaningful insights of how to improve certain properties selectively.