Absorption spectra of first-row transition metal complexes of bacteriochlorins: a theoretical analysis

A theoretical study on a family of divalent transition metal bacteriochlorin complexes (M-BC, where M = Mn, Fe, Co, Ni Cu, and Zn) has been carried out to elucidate their potentialities as active molecules in photodynamic therapy (PDT). To draw a complete picture of their electronic properties, both for the ground and excited states, these complexes have been studied by the means of density functional theory (DFT). The time-dependent DFT (TDDFT) approach was used to interpret the electronic spectra, while solvent effects were taken into account by explicitly considering both two water molecules coordinated to the central metal atom and the contribution from the solvent bulk. Particular attention has been devoted to the analysis of the so-called Q bands, since these can be particularly important for medical applications. Metal substitution and environment (solvent) effects have been analyzed, and good agreement is found between computed and available UV-vis spectra. These theoretical data, especially those relative to the metallobacteriochlorins not yet completely characterized at the experimental level, could give some hints for future medical applications.