Abstract
Recent development of methods to fabricate low dimensional molecular structures has enabled tailoring their architecture using building blocks with suitably encoded structural and chemical properties. In this contribution we study structure formation in adsorbed assemblies comprising model tripod molecules equipped with terminal arm segments providing short-range directional interactions. The interaction directions were assigned in a specific anchor like pattern which enabled the creation of diverse intermolecular connections. To explore the on-surface self-assembly of these functional units the coarse grained lattice Monte Carlo simulation method was used in which the molecules were represented as collections of interconnected segments adsorbed on a triangular lattice. Our theoretical investigations focus on the effect of symmetry and size of molecular backbone on the outcome of the 2D self-assembly. The simulations revealed the formation of complex superstructures of two types including porous networks with diverse nanocavities and nanoribbons characterized by a constant width. Occurrence of these different assemblies was found to be strongly dependent on the molecular symmetry and aspect ratio, highlighting the decisive role of the arm length distribution in the tripod building block. The theoretical results of this study can be helpful in designing new low-dimensional superstructures which are stabilized be weak intermolecular interactions as well as by covalent bonds formed in on-surface reactions such as the Ullmann coupling.
Highlights
Custom synthesis of organic molecules with predefined size, shape and functionality provides diverse building blocks which have been used to create low-dimensional superstructures with emergent physico-chemical properties
To date numerous examples of adsorbed structures fabricated using functional organic building blocks have been reported, in which linear [4], bent-rod [5] and star shaped [6,7,8,9,10] units were adsorbed on such substrates as metallic surfaces and highly oriented pyrolytic graphite (HOPG)
To assess the effect of backbone shape on the self-assembly of the tecton from Fig. 1 we examined a series of test cases differing by a, b and c
Summary
Custom synthesis of organic molecules with predefined size, shape and functionality provides diverse building blocks which have been used to create low-dimensional superstructures with emergent physico-chemical properties. The nanovoids of these layered materials can provide confinement for stereoselective chemical reactions whose products can be formed only under special external geometric constraints [15] Another type of 2D molecular structures which have been obtained from the surface confined self-assembly of organic functional building blocks are the covalently bonded systems on densely packed metallic substrates [e.g. Ag, Cu or Au (111)]. A common task in the controlled creation of adsorbed structures sustained by weak and strong (covalent) intermolecular bonding is the choice of the optimal building block able to form superstructures with predefined morphology This refers to such molecular properties as size, shape/aspect ratio and intramolecular distribution of interaction centers (functional groups, halogen atoms etc.). If covalently bonded nanostructures are considered, our model can describe the formation of the corresponding precursor metal–organic structures of the Ullmann coupling reaction
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