Self-assembly and immobilization of metallophthalocyanines by alkyl substituents observed with scanning tunneling microscopy

Using CuPcOC8 and ZnPcOC8 as examples, we have demonstrated that metal phthalocyanines with covalently attached long alkyl chains can be immobilized at the interface of the organic solution and the basal plane of HOPG. Highly resolved images of the molecules can be obtained in a range of bias voltages. The high stability and close-packed assembly are attributed to the van der Waals interaction between the alkyl chains and the graphite substrate, which substantially increased the desorption barrier of the combined molecule. In addition, it is illustrated that the desorption barrier is further enhanced by the 2-D crystallization of alkane chains. It is hoped that this method could provide a complementary approach to prepare an ordered two-dimensional array of molecular films, and facilitate the STM studies of fine molecular structures.