Porphyrins Intercalated in Zn/Al and Mg/Al Layered Double Hydroxides: Properties and Structural Arrangement

Abstract

The arrangement of porphyrin molecules in the interlayer space of layered double hydroxides (LDH) has been studied by a combination of experimental techniques and molecular dynamics simulations. Intercalation of 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrins (TPPS) into ZnRAl and MgRAl LDH hosts led to a gallery height of about 15.5 Å that is comparable with the size of the porphyrin molecules. The porphyrin sulfonate groups are located at about 4 Å from the center of the hydroxide layers that is consistent with hydrogen bonding interactions between the sulfonate groups and OH groups of the layers. The aromatic ring system in the middle of the gallery is rather disordered. A large number of in-plane diffraction lines suggests that the rigidity of the porphyrin framework has a beneficial effect on the layer ordering. Molecular dynamics simulations are in agreement with the experimental results showing that the interlayer space is filled with nearly parallel porphyrin units with a slightly inclined orientation of the porphyrin planes with respect to the normal of the hydroxide layers. The photophysical experiments proved that TPPS in Mg2Al LDH hosts produce O2(1Δg) with long effective lifetimes. The LDH hybrids based on intercalated porphyrin sensitizers are suggested as new photofunctional materials.