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

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).

The Impact of Dipolar Layers on the Electronic Properties of Organic/Inorganic Hybrid Interfaces

“…[208] Dechlorination processes have also been observed for chloro-boron-subphthalocyanine (ClB-subPc) on Cu(111), although there it has been argued that only the molecules landing in Cl-down orientation undergo the dechlorination. [213]…”

van der Waals Interaction Activated Strong Electronic Coupling at the Interface between Chloro Boron-Subphthalocyanine and Cu(111)

“…The strong broadening of the PDoS found in the computational results is also present in the experimental data. In Figure 3 , we show a comparison of the UP spectra of 0.7 monolayer equivalents (as defined in ref ( 22 )) of ClB-SubPc on both Cu(111) and HOPG. On HOPG, a distinct feature representing the ClB-SubPc highest occupied molecular orbital (HOMO) centered at a binding energy ( E B ) of −1.7 eV is clearly resolved on top of the rather weak background originating from the HOPG π-band.…”

“…We used the Perdew–Burke–Ernzerhof (PBE) functional 24 complemented by a surface-screening-corrected van der Waals energy term, 25 a scheme commonly designated as PBE + vdW surf . Employing the repeated-slab approach, 26 we studied the adsorption process at a moderate packing density 22 with just one molecule in every 7 × 4√3 orthogonal surface unit cell. This represents the smallest orthogonal cell in which the energy contribution from intermolecular interactions has decayed to less than 0.1 eV.…”

“… 22 In the last case, one observes the formation of chemically different ClB-SubPc domains consisting of either dechlorinated or intact molecules. 22 Here, we focus on molecules that remain intact while adsorbing on Cu(111), while the most relevant data for dechlorinated molecules are compiled in the Supporting Information (SI). The case of intact molecules is particularly insightful for understanding the peculiarities that can arise from the interaction between a nonplanar π-electron system and a coinage metal substrate: By tuning the magnitude of van der Waals forces when simulating the ClB-SubPc/Cu(111) interface, we are able to show how the van der Waals-induced planarization of (significant parts of) the molecular backbone upon adsorption gives rise to two distinct adsorption regimes.…”

“… 22 This results, for example, in charge transfer from the surface to the chlorine atom on Ag(111), 18 in the formation of bilayer nanocrystals on Cu(111), 20 or in surface-catalyzed dechlorination of (a fraction of) the molecules on Cu(111). 22 In the last case, one observes the formation of chemically different ClB-SubPc domains consisting of either dechlorinated or intact molecules. 22 Here, we focus on molecules that remain intact while adsorbing on Cu(111), while the most relevant data for dechlorinated molecules are compiled in the Supporting Information (SI).…”