# Orientational Order of Phenyl Rotors on Triangular Platforms on Ag and Au(111)

## TL;DR

This study examines how phenyl groups arrange on silver and gold surfaces using microscopy and theory.

## Contribution

The paper reveals the orientation and dimerization of phenyl moieties on Ag(111) and Au(111) surfaces.

## Key findings

- Phenyl moieties on Ag(111) show parallel orientation within rows and 60° difference between rows.
- STM images and DFT calculations confirm dimerization of molecules on Ag(111).
- Dimerization arises from asymmetry in the phenyl wave function due to intramolecular hydrogen bonding.

## Abstract

We investigated trioxatriangulenium functionalized with
phenyl
(phenyl-TOTA) on the (111) surfaces of Ag and Au using low-temperature
scanning tunneling microscopy (STM) and density functional theory
(DFT). On Ag(111), the molecules form hexagonal arrays, and on Au(111),
honeycomb patterns are also observed. The orientations of the phenyl
moieties are resolved on both substrates. On Ag(111), the orientations
are parallel within a row and they differ by approximately 60°
between adjacent molecular rows, and STM images suggest dimerization
of the molecules. DFT calculations for Ag(111) reveal that van der
Waals interactions dominate this system. The optimized structure matches
the experimental pattern, and the simulated STM images exhibit apparent
dimerization. The dimerization results from an asymmetry of the phenyl
wave function, which reflects intramolecular hydrogen bonding between
the ligand and an oxygen atom within the triangulenium platform. The
orientation of the phenyl moieties is explained by the interaction
of each phenyl subunit with its triangulenium platform combined with
the direct long-range interaction between phenyl moieties across molecules.