Porphyrin-based metal–organic frameworks: protonation induced Q band absorption

In this work, porphyrin-based MOF nanosheets were formulated. The as-developed Gd-TCPP MOF nanosheets could be protonated significantly in an acidic solution, which greatly enhanced the UV-vis absorption at 665 nm. Also, a significant structural reorganization occurred to achieve a nanowire structure. As the center of the porphyrin had a metal coordination atom, the Q band absorption had better stability due to their inability to be protonated. These results confirm that the UV-vis absorption of the MOFs can be regulated via porphyrin protonation, and the protonation of the nanosheets in the acidic solution can be avoided by adding a metal coordination atom to the porphyrin center. We also found that zinc ions had better coordination ability with the pyrrole nitrogen of the inner porphyrin core of Gd-TCPP MOF nanosheets. Finally, the protonation of MOFs was confirmed by the yield of singlet oxygen. Also, metallic oxide nanoparticles can be formed in situ and adsorbed on the Gd-TCPP MOF nanosheets. These results are useful for the preparation of metallic oxide nanoparticle-loaded nanomaterials. This work may open novel avenues for changing the UV-vis absorption of porphyrin-based nanomaterials.