Orientational Ordering of Nonplanar Phthalocyanines on Cu(111): Strength and Orientation of the Electric Dipole Moment

TL;DR

This study investigates how chlorogallium phthalocyanine molecules orient and interact electronically when adsorbed on Cu(111), revealing a predominant 'Cl-down' configuration at low coverage and mixed orientations at higher coverage, affecting the work function.

Contribution

It provides detailed structural and electronic insights into the orientation and bonding of GaClPc molecules on Cu(111), combining experimental and computational methods.

Findings

Majority of molecules adopt 'Cl-down' configuration at sub-monolayer coverage.

Coexistence of 'Cl-down' and 'Cl-up' configurations at bilayer coverage.

Changes in work function linked to molecular orientation and bonding.

Abstract

In order to investigate the orientational ordering of molecular dipoles and the associated electronic properties, we studied the adsorption of chlorogallium phthalocyanine molecules (GaClPc, Pc=C_32N_8H_16) on Cu(111) using the X-ray standing wave technique, photoelectron spectroscopy, and quantum chemical calculations. We find that for sub-monolayer coverages on Cu(111) the majority of GaClPc molecules adsorb in a 'Cl-down' configuration by forming a covalent bond to the substrate. For bilayer coverages the XSW data indicate a co-existence of the 'Cl-down' and 'Cl-up' configuration on the substrate. The structural details established for both cases and supplementary calculations of the adsorbate system allow us to analyze the observed change of the work function.