Scanning tunneling microscopy with chemically modified tips: Discrimination of porphyrin centers based on metal coordination and hydrogen bond interactions

T. Ohshiro, T. Ito, P. Bühlmann, Y. Umezawa

Research output: Contribution to journalArticlepeer-review

61 Scopus citations

Abstract

STM gold tips chemically modified with 4-mercaptopyridine (4MP) were found capable of discriminating zinc(II) 5,15-bis(4-octadecyloxyphenyl)porphyrin (Por-Zn) from its metal-free porphyrin (Por-2H) and nickel(II) complexes (Por-Ni) in the mixed monolayers of these compounds, spontaneously formed at the solution/graphite interface. The porphyrin centers in STM images observed with 4MP-modified tips exhibited bright spots, while those measured with unmodified tips exhibited the porphyrin centers as dark depressions. The centers of Por-Zn were brighter than those of Por-2H and Por-Ni, thereby allowing the discrimination of Por-Zn from Por-2H or Por-Ni in mixed monolayers. The changes in the contrasts of porphyrin centers of Por-2H and Por-Zn/Por-Ni were explained by facilitated electron tunneling due to hydrogen bond and metal coordination interactions, respectively, between porphyrin centers and the pyridyl group of 4MP on the tip.

Original languageEnglish (US)
Pages (from-to)878-883
Number of pages6
JournalAnalytical chemistry
Volume73
Issue number5
DOIs
StatePublished - Mar 1 2001

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