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

Abstract

The self-assemblies of half-halogenated (${\mathrm{ZnPcCl}}_{8}$ and ${\mathrm{ZnPcF}}_{8}$) and nonhalogenated zinc phthalocyanine $(\mathrm{ZnPc})$ molecules on an $\mathrm{Ag}(111)$ 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 ${\mathrm{ZnPcCl}}_{8}$ and ${\mathrm{ZnPcF}}_{8}$ deposits. In the case of ${\mathrm{ZnPcCl}}_{8}$, some faults are found periodically at the end of a ripening process that are not observed in the case of ${\mathrm{ZnPcF}}_{8}$. DFT calculations on the corresponding 2D molecular networks show differences in the nature of the $\mathrm{H}\ensuremath{\cdots}\mathrm{F}$ and $\mathrm{H}\ensuremath{\cdots}\mathrm{Cl}$ 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.