Theoretical assessment of the photosensitization mechanisms of porphyrin–ruthenium(II) complexes for the formation of reactive oxygen species

Abstract

Abstract Following a thermodynamics point of view, we analyzed a set of photosensitization mechanisms (energy transfer, electron transfer) given by seven reactions applied to porphyrin–ruthenium(II) complexes ( 1 – 6 ) and their fragments (ruthenium complexes: 7 – 12 ; porphyrin: 13 ) at the B3LYP/6–31G(d,p)/LANL2DZ level of theory in condensed phase (aqueous solution). We found that whereas for the fragments ( 7 – 13 ) an energy-transfer process between their first triplet excited state (T 1 ) and molecular oxygen ( 3 O 2 ) to yield singlet oxygen ( 1 O 2 ) is favored, the privileged channels for the photosensitizers ( 1 – 6 ) correspond to production of a superoxide anion radical (O 2 − ) by electron transfer between 3 O 2 and the photosensitizers (P) either in their P(T 1 ) excited state or as a radical anion P − . The reaction channels involving P − are more exergonic by 13–17 kcal/mol with respect to the process involving P(T 1 ). These results suggest that the anionic photosensitizer would likely acquire more importance for the photodamage in the cell.