Nanoassembly of meso-tetraphenylporphines on surfaces of carbon materials: Initial steps as studied by molecular mechanics and scanning Tunneling Microscopy

We employed MM+ molecular mechanical modeling and scanning tunneling microscopy (STM) in order to analyze the initial steps of nanoassembly of meso-tetraphenylporphine H2TPP and its cobalt(II) complex CoTPP on the surface of highly-oriented pyrolytic graphite (HOPG) and single-walled carbon nanotubes (SWNTs). According to the MM+ results, monolayer H2TPP adsorption is more favorable energetically than the formation of porphyrin stacks on both graphite and nanotube sidewall; the formation of parallel interacting chains of H2TPP on graphite is more preferable than the growth of long single chains; and the assembly into a long-period helix is favored versus the formation of a short-period helix on SWNT sidewall. STM observations of CoTPP complex deposited onto bare HOPG and onto the graphite with deposited SWNTs are consistent with theoretical results. At the same time, both CoTPP single chains and ribbons were observed on HOPG. The formation of short-period helices on the nanotube sidewalls was concluded to be more likely than the long-period helical nanoassembly.