From cuvette to cells: how the central metal ion modulates the properties of phthalocyanines and porphyrazines as photosensitizers

Abstract Tetrapyrrolic macrocycles have shown increasing importance in photodynamic therapy (PDT) and diagnosis, mainly due to the possibility of fine-tuning their properties through metalation and functionalization of the ring. Thus, it is of great interest to understand how these changes affect the response of the macrocycle, in order to produce potentialized compounds for PDT, theranostic and other light-driven applications. In this review, we focus in analyzing the effect of the insertion of metal ions on some properties of porphyrazines and phthalocyanines, such as the fluorescence and singlet oxygen quantum yields, aggregation tendency, photostability and phototoxicity. We also highlight the importance of electron transfer reactions and the consequent potential that open-shell transition metal ions have in this field.