Synthesis of Metal–Organic Framework Nanosheets with High Relaxation Rate and Singlet Oxygen Yield

A novel gadolinium–porphyrin metal–organic framework (MOF) nanosheet was synthesized by coordination chelation between gadolinium(III) ions and 4,4,4,4-(porphine-5,10,15,20-tetrayl) tetrakis (benzoic acid) (TCPP). The mechanism and molecular structure of the prepared Gd-TCPP products were analyzed through the comparison of 4,4,4,4-(porphine-5,10,15,20-tetrayl) tetrakis (benzenesulfonic acid) (TPPS) and TCPP. The Gd-TCPP MOF nanosheets exhibit a high relaxation rate of 40.8 mM–1 s–1, which is better than the rates for most reported contrast agents. In addition, the photosensitive activity of the Gd-TCPP nanosheets was enhanced compared to TCPP owing to the special periodic porous structure of the MOF, indicating that the Gd-TCPP nanosheets could produce the singlet oxygen (1O2) more effectively under irradiation by visible light. Performance enhancement was observed for both metal ions and organic ligands in the Gd-TCPP MOF nanosheets. This study presents a new concept in the development bifunctional MOF nanomaterials with enhanced performance in magnetic resonance imaging and photodynamic therapy.