Influence of stress on hydrogen-bond formation in a halogenated phthalocyanine network

The self-assemblies of half-halogenated (ZnPcCl8 and ZnPcF8) and nonhalogenated zinc phthalocyanine (ZnPc) molecules on an Ag(111) surface are studied by means of a combined experimental and theoretical study. The experiments involve scanning tunneling microscopy (STM) and the theoretical study is based on the topology of electron density obtained from density-functional (DFT) calculations. STM experiments reveal different structures due to the presence or not of halogen atoms at the periphery of the molecule, but the main differences are observed comparing ZnPcCl8 and ZnPcF8 deposits. In the case of ZnPcCl8, some faults are found periodically at the end of a ripening process that are not observed in the case of ZnPcF8. DFT calculations on the corresponding 2D molecular networks show differences in the nature of the H (. . .) F and H (. . .) Cl hydrogen bonds but also differences in the equilibrium molecular lattice parameter. We demonstrate that the intermolecular interaction can be tuned by chemical substitution and that the substrate-imposed stress can have a significant influence on the molecular self-assembly.