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.
This paper studies the origin of fluorescence emissions of metalloporphyrins. The absorption spectrum of neodymium-coordinated hematoporphyrin monomethyl ether (Nd-HMME) was found to have four Q bands, which is different from the accepted knowledge (two Q bands). The absorbance of Nd-HMME was comparable to the corresponding absorbance of HMME at wavelengths of 538 nm and 572 nm, but the absorbance of Nd-HMME at wavelengths of 502 nm and 622 nm was approximately 1/30 of that at 572 nm. The doping of Nd 3+ enhanced the symmetry of HMME, and led to changes in energy level properties. Moreover, Nd-HMME still exhibited two fluorescence peaks at 624 nm and 686 nm, similar to HMME, which can be explained by the observation of a weak absorption peak of Nd-HMME at 622 nm.
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