Dimerization of Sulfur Headgroups in 4-Mercaptopyridine Self-Assembled Monolayers on Au(111) Studied by Scanning Tunneling Microscopy

Abstract

The structure of self-assembled monolayers of 4-mercaptopyridine on Au(111) has been investigated in perchloric acid solutions by in situ scanning tunneling microscopy (STM). The adsorption of this molecule yields an ordered striped structure with a rectangular (5 × ) unit cell in the double-layer potential range. The sulfur headgroup and pyridine ring moiety of the molecule were clearly imaged. The molecular image is greatly different from that reported previously. The spacing between sulfur headgroups of adjacent molecules was found to be 0.21 ± 0.02 nm. This result strongly suggests that the molecules are dimerized at the sulfur position to form a disulfide. The disulfide has a trans-CSSC skeleton, and both the pyridine rings are oriented nearly parallel to the surface. This open structure enables the direct STM observation of the sulfur−sulfur bond.

Effect of Annealing on 4- and 3-Pyridinethiol Self-assembled Monolayers on Au(111) and Au(100) Studied by High-resolution Electron Energy Loss Spectroscopy

“…[9][10][11][12][13][14][15][16] For example, 4-pyridinethiol (4-PySH), which is a popular molecule for use as a modifier, has been studied not only as an electron-transfer promoter for cytochrome c, 9,10 but also from the perspective of fundamental and structural chemistry using surface-sensitive techniques, such as surface-enhanced Raman spectroscopy (SERS), [17][18][19] surface enhanced infrared absorption spectroscopy (SEIRAS), [20][21][22] and scanning tunneling microscopy (STM). [23][24][25][26][27][28][29] 3-Pyridinethiol (3-PySH), which is a structural isomer of 4-PySH, is also expected to be a good modifier for the electron transfer of cytochrome c. Our preliminary results regarding an EC-STM structural investigation of 3-PySH SAM in an acidic solution were almost identical to those for 4-PySH SAM. To elucidate the differences in the surface functionalities of 3-PySH and 4-PySH SAMs, further structural analysis is needed to determine the molecular orientation.…”

Potential-Induced Structural Change in a Self-Assembled Monolayer of 4-Methylbenzenethiol on Au(111)

“…24,25 Another possible suggestion for the small intermolecular distances is the sulfur-sulfur dimerization at thiolate headgroups. 27,55 The dimerization at the sulfur headgroups for the decanethiol 55 and 4-mercaptopyridine 27 SAMs on Au(111) led to a sulfur-sulfur spacing of 0.21-0.22 nm. We suggest that at potentials negative of 0.3 V, a decrease of the interaction between 4-MBT and the substrate could drive the thiolate headgroups to form weak dimers.…”

Theoretical studies of Pd metal deposition on the √3×√3 4-mercaptopyridine self-assembled monolayer

“…Studies featuring scanning tunnelling microscopy (STM) have reported √ 3 × 1 [24,25], √ 3 × 5 [26,27], √ 3 × 7 [25] and √ 3 × 10 [24] overlayers under different electrochemical conditions. However, given the difficulties in calibrating the STM measurements for such SAMs on metal substrates, even additional structures might be possible [21,22].…”