Influence of molecular shape and interaction anisotropy on the self-assembly of tripod building blocks on solid surfaces

Molecular shape and directionality of intermolecular interactions are important factors which affect structure formation in adsorbed overlayers. In this contribution, using theoretical methods we demonstrate the importance of these factors in the surface-confined self-assembly of tripod-shaped organic molecules with reduced symmetry. To that end a lattice Monte Carlo model is proposed in which the molecules are represented in a coarse grained way, as flat rigid structures comprising a few connected segments adsorbed on a triangular lattice. The calculations are performed for the molecules equipped with terminal active centers providing directional intermolecular interactions. These results are compared with analogous data obtained for C-3-symmetric units and Y-shaped molecules whose all composite segments are active. The simulated results show that for the directional interactions, the reduction of molecular symmetry leads to the formation of disordered, glassy, porous networks with hexagonal nanovoids of different shapes. Moreover, it is demonstrated that the interaction mode involving all molecular segments of the asymmetric building blocks is responsible for the formation of compact patterns. Relative thermal stability of the simulated assemblies is also compared, highlighting deciding role of the interaction mode in stabilization of the adsorbed superstructures. The findings of our theoretical investigations can be helpful in designing new molecular blocks and programming their interactions to create 2D molecular superstructures with tunable morphology and functions.