Chronological change from face-on to edge-on ordering of zinc-tetraphenylporphyrin at the phenyloctane-highly oriented pyrolytic graphite interface.

The self-assembled structure of alkoxy- and N-alkylcarbamoyl-substituted zinc-tetraphenylporphyrin at the liquid-highly oriented pyrolytic graphite (HOPG) interface was observed by using scanning tunneling microscopy. The alkoxy porphyrin showed a phase transition from face-on to edge-on ordering. The phase transition requires the close-packed structure of alkoxy porphyrin. The chronological change of the ordering was traced to show the existence of several types of Ostwald ripening including two-step phase transition from small edge-on to face-on and then further to edge-on orderings. On the other hand, the N-alkylcarbamoyl porphyrin showed persistent edge-on ordering, and the ordering was analyzed by the Moiré pattern. Although the edge-on ordering is observed only in the nonpolar solvent, the orderings have potential applications in the charge and energy transfer.