Self-directed Assembly And Properties Of The Ordered Porphyrin Composite Films

The performance of three-dimensional metal-organic frameworks (MOFs) films is greatly affected by its micro-structure, assembly ways and methods. Therefore, how to design an assembly unit and fabricate the ordered films with ideal properties becomes one of the important research topics. Metalloporphyrins with high thermal and chemical stability have showed a wide range of applications in optoelectronic devices, catalysis and molecular recognition. Moreover, its structure is easy to be modulated. As a consequence, the structure of MOFs films can be modified more finely, and its performance can be enriched if metalloporphyrin molecules were used as assembly units. In this paper, a novel porphyrin cobalt monomer was designed and synthesized. Various stable and orderly porphyrin MOFs composite thin films on various substrates were quickly achieved by self-directed assembly of the porphyrin cobalt monomer. And then, the relationship between the structure and performance of the films was investigated. The main contents are summarized as follows:5,10,15,20-Tetra (4-carboxyphenyl) porphyrin and 5,10,15,20-tetra (4-carboxyphenyl) porphyrin cobalt were quickly prepared by using a modified Alder-Longo method. It was found that it was important to introduce oxygen in the reaction. The products were characterized and confirmed by UV-vis spectrum, IR spectrum and mass spectrum.A new porphyrin monomer was synthesized by acyl chlorination and silanization of the 5, 10,15,20-tetra (4-carboxyphenyl) porphyrin cobalt. The monomer was characterized by UV-vis spectrum, FTIR spectrum and mass spectrum. For the monomer, its peripheries bear four sisesquioxanes, and its centre bears cobalt ion, which are vital to realize the self-directed assembly of the porphyrin monomer in three-dimensional direction.Under the inducement of 4,4’-bipyridine, the porphyrin monomer was arranged orderly, and then hydrolysis-polymerized after introducing a small amount of HCl. Therefore, a three-dimensional ordered porphyrin MOFs film can be achieved by self-directed assembly of the porphyrin monomer in various substrates. In the process of self-directed assembly of the porphyrin composite thin films, the central cobalt ion of porphyrin macrocycle coordinated with 4,4’-bipyridine in axial direction, and further self-directedly assembled in the horizontal direction by the hydrolysis-polymerization of sisesquioxanes linking on the peripheries of porphyrin macrocycle. The microstructure, morphology and electric properties of the MOFs film were characterized by XRD, BET, TGA, AFM, TEM and electrochemical methods, respectively. The results showed that the porphyrin MOFs films possessed mesoporous structure. C-Si-O-Si-C network in the horizontal direction can reduce the bulk density of porphyrins and the direct interactions between molecules. Therefore, the porphyrin MOFs film with higher heat stability and photoelectronic performance was achieved.With 4,4’-bipyridine,4-(2-pyridin-4-ylethynyl) pyridine and 5,15-di (4-pyridyl)-10,20-diphenylporphyrin as bidentate-bridged ligands, respectively, three orderly porphyrin MOFs films were prepared by self-directed assembly of the porphyrin cobalt monomer. The influence of the size and conjugated level of the ligands on the microstructure, morphology and photoelectric property of the porphyrin MOFs films were studied in detail. It is found that the interlayer space, thickness and performance of the composite thin films can be tuned by controlling the size, conjugated level and the quantity of the bidentate-bridged ligand.