Chiral Organization and Charge Redistribution in Chloroaluminum Phthalocyanine on Au(111) Beyond the Monolayer

The nontrivial effect of molecular dipoles on the surface work function of metals is explored for the unidirectional ordered arrays forming the first and second layers of chloroaluminum phthalocyanine on Au(111). This phthalocyanine is a nonplanar molecule with permanent electric dipole perpendicular to its molecular π-plane that can adopt two distinct configurations (Cl-up and Cl-down) when adsorbed on surfaces. The ordered array forming the first layer is known to consist of all Cl-up molecules, whereas the less-studied second layer is formed by molecules in the Cl-down configuration. The inverted orientation of the molecules in these two layers constitutes our benchmark system to investigate the influence of the dipole array orientation on the surface work function. The present study includes an experimental and theoretical approach that combines diverse imaging and spectroscopic scanning probe microscopies, in ultrahigh vacuum, with first-principles density functional theory-based atomistic simulations. Experiment and theory show a chiral organization transferred from the first layer to the growing film that is reflected in the electronic structure. We demonstrate that the obtained surface work function changes are smaller in magnitude than expected from a dipolar approximation because of charge rearrangement at and beyond the monolayer. We provide understanding of the crucial interplay between the interlayer and organic/metal interactions and quantify their effect on the electron density distribution and on the work function changes.This work has been supported by the Spanish Government under projects MAT2013-47869-C4-1-P, MAT2015-72848- EXP /AEI and MAT2016-77852-C2-1-R (AEI/FEDER, UE) and the Generalitat de Catalunya 2017 SGR 668. R. P-R. thanks financial support through BES-2014-067942. We acknowledge the specific agreement between ICMAB-CSIC and the Synchrotron Light Facility ALBA and the Spanish MINECO through the project MAT2015-68994-REDC and the “Severo Ochoa” Program for Centers of Excellence in R&D (SEV-2015-0496). J.I.M. acknowledges the financial support by the Spanish MINECO via grant no. MAT2017-85089-C2-1- R and the “Ramon y Cajal ́ ” Program (grant no. RYC-2015- 17730), and the EU through the Innovation Program (grant 696656: Graphene Core1. Graphene-based disruptive technologies), as well as the use of computing resources from CTICSIC.Peer reviewe