Computational investigations of electron transfer in transition metal complexes

Transition metal complexes and their properties have been of interest to scientists for many decades. These complexes can be used to gain an understanding of fundamental processes, such as electron transfer, as well as be used in real-life applications, such as for the treatment of certain cancers. This thesis characterises, with the use of quantum chemical calculations, the ground and excited state properties of a family of platinum donor-bridge-acceptor systems. These systems contained a naphthalenediimde acceptor and a phenothiazine/ methoxy-phenothiazine donor. Recently, the use of targeted infrared excitations has been shown to influence the outcome of light-induced electron transfer reactions in families of platinum donor-bridge-acceptor systems. This thesis shows how the similarity of vibrational normal modes to the non-adiabatic coupling vector and the gradient difference vector, which is the geometry dependence of the energy gap between a pair of states, can be used to identify potential vibrations that modulate coupling between states and in turn influence the outcome of electron transfer processes for a number of platinum donor-bridge-acceptor systems. For the majority of complexes investigated the acetylide stretching vibrations were shown to be key modulating modes, that when excited could influence the ratio of the product states. In addition a series of platinum acceptor-bridge-acceptor complexes were investigated to determine the effect of bridge length on their photo-physical properties. Finally, a variety of ligands and their associated σ-Hammett parameters parameters were used to tune the photo physical properties of iridium complexes. It was found that for these complexes substitution with electron donating groups influenced the electronic spectra, the frontier molecular orbitals and the characters of the excited states most strongly, leading to a lowering of the excitation energy of the main absorption feature.
A linear correlation between the Hammett parameter and the maximum in the absorption spectrum was found for certain substitution positions, which is explained starting from the definition of the Hammett parameter.