X-ray absorption (XAS) and resonant inelastic scattering (RIXS) of a number of Mn 2+,3+,4+ complexes relevant for photo-electrooxidation of water is studied theoretically using the RASSCF/RASSI approach. This enables us to quantify spin-orbit coupling induced mixing of states with different multiplicities in the valence-and core-excited electronic states, evidencing the mostly spin-forbidden character of transitions in RIXS spectra. The notably different patterns of spectroscopic features in this series of substances not only provide insight into their electronic structure, but open the possibility for tracing redox evolution by means of X-ray spectroscopy.Specific findings deduced from the analysis of the shape of the RIXS spectra concern the gap between the ground and first excited valence states relevant for catalytic activity. This gap is substantially lower for Mn 3+ as compared to the even oxidation states.

Electronic excitation energy transfer along a molecular wire depends on the relative orientation of the electronic transition dipole moments of neighboring chromophores. In porphycenes this orientation is changed upon double proton transfer in the electronic ground state. We explore the possibility to trigger such a double proton transfer reaction by means of an infrared pump-dump laser control scheme. To this end a quantum chemical characterization of an asymmetrically substituted porphycene is performed using density functional theory. Ground state geometries, the topology of the potential energy surface for double proton transfer, and S 0 →S 1 transition energies are compared with the parent compound porphycene and a symmetric derivative. Employing a simple two-dimensional model for the double proton transfer, which incorporates sequential and concerted motions, quantum dynamics simulations of the laser driven dynamics are performed which demonstrate tautomerization control. Based on the orientation of the transition dipole moments this tautomerization may lead to an estimated change in the Förster transfer coupling of about 60%.

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