Scanning Tunneling Microscopy with Chemically Modified Tips:  Discrimination of Porphyrin Centers Based on Metal Coordination and Hydrogen Bond Interactions

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...

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Bibliographic Details
Published in:Analytical chemistry (Washington) 2001-03, Vol.73 (5), p.878-883
Main Authors: Ohshiro, Takahito, Ito, Takashi, Bühlmann, Philippe, Umezawa, Yoshio
Format: Article
Language:English
Subjects:
Chemistry
Exact sciences and technology
General and physical chemistry
Hydrogen
Hydrogen Bonding
Metals
Metals - chemistry
Microscopy, Scanning Tunneling - methods
Porphyrins - chemistry
Scientific imaging
Solid-liquid interface
Surface physical chemistry
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Summary: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.
ISSN:0003-2700
1520-6882
DOI:10.1021/ac001056e