Lateral Interactions and Order–Disorder Phase Transitions of Metal Phthalocyanines on Ag(111)

The intermolecular interaction among phthalocyanine molecules deposited on Ag(111) has been investigated at submonolayer coverages. By means of infrared absorption spectroscopy and spot-profile analysis low-energy electron diffraction, unambiguous evidence for an attractive between neighboring titanyl-phthalocyanine (TiOPc) is found dilute layers, which in contrast to the repulsion reported copper-phthalocyanine (CuPc)/Ag(111) system. Accordingly, formation dense two-dimensional islands TiOPc with a well-defined long-range order (commensurate phase) observed upon cooling temperatures below 75 K, while disordered arrangement retained adsorbed CuPc. Using density functional theory (DFT) calculations as guide, these differences have traced competition van der Waals repulsive electrostatic interactions. Specifically, vertically oriented molecular dipoles are substantially smaller compared CuPc due compensation oppositely dipole moments arising from Pauli push-back effect one hand internal associated axial Ti–O group other. A detailed account comparison molecule–substrate interaction, binding geometries, interactions surface provided theoretical based DFT.