Organization of Vanadyl and Metal-Free Tetraphenoxyphthalocyanine Complexes on Highly Oriented Pyrolytic Graphite in the Presence of Paraffinic Solvents: A STM Study

Abstract

Scanning tunneling microscopy (STM) is employed to demonstrate that the presence of the vanadyl ion (VO 2+ ) in the 2,9,16,23-tetraphenoxy-29 H,31 H -phthalocyanine complex (VOPcPhO) has a pronounced effect on the organization of the complex at the highly oriented pyrolytic graphite (HOPG)− n -alkyl benzene ( n = 6, 7, 8, and 10) interface. VOPcPhO forms at least three different stable architectures, as compared to only one type of structure resulting from the adsorption of the metal-free tetraphenoxyphthalocyanine analog (H 2 PcPhO) on HOPG under conditions similar to VOPcPhO. All three observed VOPcPhO monolayer structures have high packing density and are commensurate with the underlying graphite lattice, whereas H 2 PcPhO forms a lower packing density incommensurate adlayer. The VOPcPhO structures display a small rectangular unit cell (1 molecule/cell) with lattice vector lengths of 1.28 and 1.48 nm, a larger rectangular unit cell (6 molecules/cell) with lattice vector lengths of 4.43 nm 2.98 nm, and an oblique unit cell (2 molecules/cell and α = 84.7°) with lattice vector lengths of 1.48 and 2.99 nm. As a second layer begins to form, it preferentially adds to the large unit cell, keeping those lattice parameters, but with only four molecules per cell. The H 2 PcPhO adlayer achieves an oblique unit cell (α = 74° and 1 molecule/cell) with 1.58 and 1.68 nm length lattice vectors. On the basis of combined experimental results and theoretical calculations, we propose models for the observed molecular organizations.