Photodynamic therapy based on porphyrin-based metal–organic frameworks

Porphyrins and their derivatives have excellent photophysical and electrochemical properties, which have attracted great interest in the fields of catalysis, biosensing, gas storage, solar cells, biomedicine, etc. However, the inherent limitations, such as self-quenching, weak absorption at biological spectral windows and poor photochemical stability, severely hinder their applications in biomedicine, especially in the field of photodynamic therapy (PDT). In recent years, metal-organic frameworks (MOFs) have received increasing attention as a class of hybrid porous coordination polymers assembled from metal ions/secondary building units (SBUs) and organic linkers. By introducing porphyrins into MOFs via the encapsulation in the pores as well as grafting on the surface to form porphyrin@MOFs or using porphyrins as organic linkers to construct porphyrin-MOFs, not only the unique properties of porphyrins and MOFs are combined, but also the limitations of porphyrins are overcome and their applications are facilitated in the biomedicine field. This article reviews important synthetic strategies of forming porphyrin-based MOFs (including porphyrin@MOFs and porphyrin-MOFs), which focuses on the recent research achievements and progress in PDT and tumor therapy fields. Furthermore, by carefully designing the composition of MOFs (such as the modification of organic linkers), MOFs could respond to the tumor microenvironment for on-demand treatment. In addition, some other strategies, including chemotherapy, photothermal therapy (PTT) and the latest cancer immunotherapy, are also combined in the review. Finally, the challenges and prospects in biomedical applications of this class of emerging materials are discussed.