Structural properties of tetra-tert-butyl zinc(II) phthalocyanine isomers on a Au(111) surface

The self-assembly behavior of the mixture of tetra-tert-butyl zinc(II) phthalocyanine (TB-ZnPc) isomers on a Au(111) surface has been investigated by means of scanning tunneling microscopy (STM). Four tert-butyl groups are added to four peripheral benzene rings of zinc(II) phthalocyanine, which gives the planar molecules a three-dimensional structure. Two possible substituting locations for each tert-butyl group result in a mixture of structural isomers, which are easily identified by STM. Two different structures have been distinguished in the monolayer regime depending on the preparation procedure. One is a quasi-ordered structure whereby the molecules are arranged in the closest-packed way, and the second is an ordered structure in which the molecules are arranged side by side. The more ordered molecular network in the latter is considered to be a consequence of unification of TB-ZnPc isomers.