Spectroscopy and photochemistry of transition metal complexes : a quantum chemical study
Transition metal complexes possess unique chemical, photoredox and spectroscopical properties that makes them promising candidates as light harvesting antennae or photocatalytic centers in many photochemical devices, such as e.g. Ru(II) polypyridyl complexes in dye sensitized solar cells. The knowledge of the photochemical properties of these complexes is therefore of paramount importance to optimize their performance in these devices. To this aim, the computation of excited states and photochemical properties can provide useful hints to guide molecular design strategies. Unfortunately, the description of electronic excited states is still far from routine, as compared to ground state studies, and even more that of systems containing metal atoms. The present work focuses on the computation of the spectroscopic and photochemical properties of transition metal complexes. First, a benchmark study on the excited states of a Ru(II) polypyridyl complex with quantum chemical and TD-DFT methods is presented. After electronic excitation, the possibilities that a molecule has for deactivating are plenty and usually such relaxation processes compete one to each other. The second main part of this thesis is then devoted to disentangling photophysical and photochemical mechanisms on several Ru(II) polypyridyl and Pt complexes with the help of quantum chemical calculations. Thereby, some photophysical properties, such as e.g. radiative decay rates have been computed to rationalize e.g. the fine-tuning in the emissive properties. Other photochemical studies dealing with the emissive properties of Ir complexes, which are used as phosphors in organic light-emitting diodes, are also presented along this thesis. Finally, in order to get information about quantum yields and lifetimes of the excited states, ab-initio excited state reaction dynamical studies are mandatory. This is still a challenge for transition metal complexes and in this thesis we have performed model surface-hopping molecular dynamics simulations in a small organic system, i.e. 2H-Azirines, which exhibits wavelength dependent C-N and C-C bond photoactivation.