Self-assembly of strongly dipolar molecules on metal surfaces

Abstract

The role of dipole-dipole interactions in the self-assembly of dipolar organic molecules on surfaces is investigated. As a model system, strongly dipolar model molecules, p-benzoquinonemonoimine zwitterions (ZI) of type C 6 H 2 (· · · NHR) 2 (· · · O) 2 on crystalline coinage metal surfaces were investigated with scanning tunneling microscopy and first principles calculations. Depending on the substrate, the molecules assemble into small clusters, nano gratings, and stripes, as well as in two-dimensional islands. The alignment of the molecular dipoles in those assemblies only rarely assumes the lowest electrostatic energy configuration. Based on calculations of the electrostatic energy for various experimentally observed molecular arrangements and under consideration of computed dipole moments of adsorbed molecules, the electrostatic energy minimization is ruled out as the driving force in the self-assembly. The structures observed are mainly the result of a competition between chemical interactions and substrate effects. The substrate's role in the self-assembly is to (i) reduce and realign the molecular dipole through charge donation and back donation involving both the molecular HOMO and LUMO, (ii) dictate the epitaxial orientation of the adsorbates, specifically so on Cu(111), and (iii) inhibit attractive forces between neighboring chains in the system ZI/Cu(111), which results in regularly spaced molecular gratings. C 2015 AIP Publishing LLC. [http://dx

Electrostatic charge-charge and dipole-dipole interactions near the surface of a medium with screening non-locality (Review Article)

“…Hence, the smallness of the former parameter is ensured at 1 L >> Å. It is appropriate for loose adsorbate structures [17,21,22,34,[39][40][41][42][43]. At the same time, the parameter Z is the sum of the charges' distances from the substrate, z z′ + (see Eq.…”

“…Hence, it is also quite natural to consider their interactions as electrostatic charge-charge [17,21,22,39,40] or dipole-dipole ones [34,[41][42][43]. Similarly to the case of polarization (image) forces, the proper electrostatics must be non-local and should take into account the quantum-mechanical nature of charge carriers.…”

“…This is a first step in the consideration of the substrate influence on the adsorption processes and the kinetics of adsorbate arrangement on the surface. Anyway, the dipole-dipole interaction is a main input to be used in the problems of surface dipole-lattice structures, which serve as models of adsorbate patterns on various substrates [34,43,[64][65][66][67][68][69][70][71][72].…”

“…The pairwise interaction considered here can serve as an input in the calculations of possible electric-dipole lattice structures [34,43,66,68,71,72]. Therefore, the whole procedure of such calculations should take into account the substrate-induced distortion of lateral interactions.…”

Changes in molecular film metallicity with minor modifications of the constitutive quinonoid zwitterions

“…No corrections were made for molecular interactions and nal state effects. This is typical of the density functional theory applied to quinonoid zwitterions, even when using the extended 6-31G* basis set, 5d,5i,5j, 8,17,18,19,20 but there are some solid state calculations that have been compared with experiment. …”