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-29H, 31H-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 2PcPhO) 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 2PcPhO 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 2PcPhO 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. © 2008 American Chemical Society.