Sticking with the Pointy End? Molecular Configuration of Chloro Boron-Subphthalocyanine on Cu(111).

Nahid Ilyas,Oliver T Hofmann,Percy Zahl,Egbert Zojer,Rocio Cortes,Peter Sutter,Shashank S Harivyasi,Oliver L A Monti

doi:10.1021/acs.jpcc.5b11799

Abstract

In this combined low-temperature scanning tunneling microscopy (STM) and density functional theory (DFT) study, we investigate self-assembly of the dipolar nonplanar organic semiconductor chloro boron-subphthalocyanine (ClB-SubPc) on Cu(111). We observe multiple distinct adsorption configurations and demonstrate that these can only be understood by taking surface-catalyzed dechlorination into account. A detailed investigation of possible adsorption configurations and the comparison of experimental and computational STM images demonstrates that the configurations correspond to “Cl-up” molecules with the B–Cl moiety pointing toward the vacuum side of the interface, and dechlorinated molecules. In contrast to the standard interpretation of adsorption of nonplanar molecules in the phthalocyanine family, we find no evidence for “Cl-down” molecules where the B–Cl moiety would be pointing toward the Cu surface. We show computationally that such a configuration is unstable and thus is highly unlikely to occur for ClB-SubPc on Cu(111). Using these assignments, we discuss the different self-assembly motifs in the submonolayer coverage regime. The combination of DFT and STM is essential to gain a full atomistic understanding of the surface–molecule interactions, and our findings imply that phthalocyanines may undergo surface-catalyzed reactions hitherto not considered. Our results also indicate that care has to be taken when analyzing possible adsorption configurations of polar members of the phthalocyanine family, especially when they are adsorbed on comparably reactive surfaces like Cu(111).

Highlights

In this combined low-temperature scanning tunneling microscopy (STM) and density functional theory (DFT) study, we investigate self-assembly of the dipolar nonplanar organic semiconductor chloro boron-subphthalocyanine (ClB-SubPc) on Cu(111)
Our results indicate that care has to be taken when analyzing possible adsorption configurations of polar members of the phthalocyanine family, especially when they are adsorbed on comparably reactive surfaces like Cu(111)
Well-defined structure−function relationships relating molecular structure to thin film structure and interfacial energy level alignment have been difficult to establish for many organic semiconductor/metal surface combinations due to the high structural diversity of the organic molecules of interest.[1−7] This is further compounded by frequent polymorphism and often complex phase diagrams for organic thin film growth.[8−10] The root cause lies likely in the fact that the important interactions, ranging from dipole repulsion and van der Waals interactions to charge-transfer related forces, occur on comparable energy scales

Summary

Introduction

Well-defined structure−function relationships relating molecular structure to thin film structure and interfacial energy level alignment have been difficult to establish for many organic semiconductor/metal surface combinations due to the high structural diversity of the organic molecules of interest.[1−7] This is further compounded by frequent polymorphism and often complex phase diagrams for organic thin film growth.[8−10] The root cause lies likely in the fact that the important interactions, ranging from dipole repulsion and van der Waals interactions to charge-transfer related forces, occur on comparable energy scales This makes predictive insight into the molecular adsorption and resulting thin film structure for arbitrary organic semiconductors still challenging.[11−13].

Methods

Results

Conclusion