Interplay of the metal surface electronic state and non-covalent molecular bonds in synergistic molecular assembly formation on Au(111)

Non-covalent bonds are fundamental for designing self-assembled organic structures with potentially high responsivity to mechanical, light, and thermal stimuli. We present here results of joint scanning tunneling microscopy measurements and density functional theory (DFT) calculations that reveal the interplay between synergistic interactions of multiple highly-directional bonds of a pure electrostatic nature and the metal surface states that give rise to the assembly of one molecular specie, namely 4,7-dibromobenzo[c]-1,2,5-thiadiazole (2Br-BTD), in two different patterns on Au(111). Our DFT calculations find the 2Br-BTD layer to be buckled and the molecules to be weakly adsorbed on the Au(111) surface at a distance of 3.38 Å. Interestingly, the Au(111)’s surfaces state shift by 65 meV towards the Fermi level. More importantly, despite the weak interaction between the molecular film and the surface, there is hybridization of the surface states and molecular orbitals giving rise to new partially occupied orbitals of the organic molecules. Our work indicates that despite the weak adsorption of organic molecules, the Au(111) surface impacts the electronic and geometric structure of the 2Br-BTD layer.