ИСТИНА

A new strategy of bilayer porphyrin-graphene template formation to initiate the assembly of various surface metal-organic frameworks on solid substrates is proposed. A simple strategy allows us to create for one step a complex bilayer template on the liquid surface from an organized film of functionalized porphyrin and an adsorption layer of graphene oxide (GO). After transferring of bilayer to a solid substrate by the Langmuir-Blodgett (LB) technique, it is used as a template for assembling of SURMOFs. An important aspect of the proposed approach is the possibility of realizing the known stabilization effect of the 2D graphene structure by the surface of the substrate on which it is applied. In the free state, graphene has a wavy surface with a lateral dimension of a separate inhomogeneity of up to 10 nm and a height of about 1 nm. We believe that to obtain extended homogeneously oriented films of porphyrin-reinforced GO, this approach has certain advantages over the assembly of pure GO monolayer by the Langmuir-Blodgett technique, or by vertical transfer from a liquid-liquid interface. The behavior of monolayers of tetrapyridylporphyrin [1,2] and tetracarboxyphenylporphyrin [2] zinc complexes on the surface of deionized water, aqueous solutions of zinc acetate, GO and GO in the presence of zinc acetate is studied. Using the Langmuir surface balance, in situ fiber optic UV reflection-absorption spectroscopy and fluorescence spectroscopy, the molecular organization of the porphyrin films on surface of pure water is determined and its change under the effect of zinc cations and/or the adsorption layer of the GO is demonstrated. Bilayer templates of ZnTPyP/GO/ZnAc2 and ZnTCPP/GO/ZnAc2 were transferred from air-water interface onto the silicon wafer via LB technique. Figure 1a shows that the film based on ZnTPyP consists of a discontinuous openwork net with clearly discernible elements in the form of flat, irregularly shaped annular figures arranged on the sheets of GO. Network is formed because of branching of 1D elements. In the case of a ZnTCPP film obtained on the surface of an aqueous solution of GO and zinc acetate, the SEM micrograph (Figure 1b) demonstrates high film uniformity over a large area. The film consists of elements-grains, densely packed on the sheets of the GO. The deposited bilayer templates were then used for the epitaxial assembly of two different SURMOFS: ZnTPyP/ZnAc2 and ZnTCPP/ZnAc2 [3]. To study the structure of SURMOFs X-ray diffraction method was used. Thus, the proposed approach to assembling the templates for SURMOFs is interesting in that when transferring a bilayer from firmly bonded layers of porphyrin and GO onto a solid substrate, the effect of the latter on the change in the structure of the organic layer is screened by the GO layer. At the same time, thanks to the features of the GO, the bilayer is firmly fixed on a solid substrate. This allows us to solve immediately several pressing problems of the formation of SURMOFs: (1) creation of templates on a solid substrate of any nature without the use of self-organized monolayers in the epitaxial growth of coordination polymers, (2) exclusion of the influence of a solid substrate on the restructuring of the monolayer structure when it is transferred from the liquid surface by the Langmuir- Blodgett method, (3) prevention of the desorption of this monolayer when the film is enlarged by LB methods or layer-by-layer assembly.