Structures of Self-Assembled Monolayer of Squaraine Molecules Adsorbed on Highly Oriented Pyrolytic Graphite and Au(111) Substrates

Abstract

Molecular arrangements of squaraine (SQ) molecules formed on highly oriented pyrolytic graphite (HOPG) and Au(111) substrates in phenyloctane solution were studied by scanning tunneling microscopy (STM). On HOPG, SQ molecules without hydroxyl groups formed row arrangements, in contrast to the herringbone structures previously observed for the SQ molecules with hydroxyl groups, indicating that the chemically added hydroxyl groups play an important role in the formation of the herringbone arrangement. On the other hand, the observed molecular structures on the Au(111) substrate were completely different from those on the HOPG substrate, which was attributed to the specific interactions between the two anilino moieties in a SQ molecule and Au(111) lattices. The obtained results indicate the possibility of structural control of SQ molecules, namely, the photo-absorption property, by changing the kinds of functional groups and substrates.