Fabrication And Modulation Of One-and Two-Dimensional Assemblies Based On Melamine Derivatives

Self-assembly refers to the process that molecules associate spontaneously through non-covalent interactions to form well-defined structures.The self assembly of organic molecules will lead to the formation of supramolecular structures with different dimensions,exhibiting extraordinary properties and functions.The realization of controlled self assembly is crucial for the fabrication of micro/nano structures with specific morphologies and functions.This thesis is focused on the controlled fabrication of two-dimensional(2D)assemblies or one-dimensional(1D)core-shell structures based on the self assembly of melaminium derivatives.We propose a new strategy to fabricate the above-mentioned structures by lowering the dimensionality of three-dimensional(3D)networks.By means of molecular modification or introducing additives,we can restrict the growth of 3D structures in one or two directions,resulting in the formation of 2D assemblies or 1D core-shell structures.The main results of the thesis are as follows:1)Based on the structural analysis of melamine hydrochloride,we introduced two alkyl chains to restrict the growth of one direction,while the interactions in the other two directions are well preserved,thus leading to the formation of 2D microsheets.Replacing the alkyl chains with allyl groups will also generate 2D structures.Moreover,the assembly and disassembly of microsheets can be reversibly controlled through alternating addition of acid and base.Even the aspect ratio of the rectangular microsheets can be tuned by varying the amount of hydrochloric acid.2)Two kinds of dialkylated melamine with identical or different length of alkyl chains can self-assemble with hydrochloric acid to form 2D assemblies.The growth mechanism of melaminium derivatives with identical alkyl chains is revealed to be layer growth,while melaminium derivatives with different alkyl chains adopt a spiral growth mechanism.This line of research may provide inspirations for the fabrication of ultrathin 2D assemblies and spiral structures from organic molecules.3)Through the co-assembly of dimethyl melamine hydrochloride and melamine derivatives with pyrene groups,we can realize one-pot fabrication of 1D core-shell structures.Such 1D structures can be destroyed upon exposure to ammonia,accompanying significant change in fluorescence of pyrene.Furthermore,the growth mechanism was revealed by X-ray diffraction.1D core-shell structures with tunable shell compositions can be easily fabricated.Moreover,the length and width of such 1D structures can be tuned by varying the molar ratio of core/shell compositions or their total concentration.