Photochemical and photophysical reactions in transition-metal complexes occur when the compound is excited to higher-lying electronic states via light absorption. The complex can then experience a cascade of processes involving different electronic states connected through the motion of the molecules' nuclei. The participation of different electronic states introduces new flexibility to the system by opening up reaction pathways beyond the ones that are accessible in thermal ground-state chemistry. This flexibility then lays the foundation to the many application found in photochemistry , covering areas as diverse as catalysis, memory storage, energy storage, display and lighting technology, or medicine. While a blessing for applications, the flexibility is a challenge for the rational design of photoactive materials, as it needs to control not only the properties of the different electronic states but also the motion connecting them. The fast time scale on which photochemical reactions often occur not only further limits the influence that can exerted on them, but also increases the difficulty to study such reactions in experiment. These complications are felt especially when dealing with transition-metal a Institute of Theoretical Chemistry, Faculty of Chemistry, University of Vienna, Währingerstr. 19, 1090 Vienna, Austria; E-mail: jan.patrick.zobel@univie.ac.at † Electronic Supplementary Information (ESI) available: See DOI: 00.0000/00000000. complexes as compared to many organic photoactive compounds they typically posses a greater amount of electronic states at low energies, which can participate in the photochemical reactions, and are of larger size, carrying many more nuclear degrees of freedom. It is then, that theoretical investigations become invaluable as they offer an alternative access to study and predict the properties of photoactive compounds.