Clarifying interfacial electronic effects on molecular adsorption is significant in many chemical and biochemical processes.H ere,w eu sed STM breaking junction and shellisolated nanoparticle-enhanced Raman spectroscopyt op robe electron transport and adsorption geometries of 4,4'-bipyridine (4,4'-BPY) at Au(111). Modifying the surface with 1-butyl-3methylimidazolium cation-containing ionic liquids (ILs) decreases surface electron density and stabilizes av ertical orientation of pyridine through nitrogen atom s-bond interactions,r esulting in uniform adsorption configurations for forming molecular junctions.Modulation from vertical, tilted, to flat, is achieved on adding water to ILs,l eading to an ew peak ascribed to CC stretching of adsorbed pyridyl ring and 316 %m odulation of single-molecule conductance.T he dihedral angle between adsorbed pyridyl ring and surface decreases with increasing surface electronic density,e nhancing electron donation from surface to pyridyl ring.
Room-temperature
ionic liquids (RTILs) emerged as ideal solvents,
and bipyridine as one of the most used ligands have been widely employed
in surface science, catalysis, and molecular electronics. Herein,
in situ shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS)
and STM break junction (STM-BJ) technique has been employed to probe
the electrochemical process of bipyridine at Au(111)/IL interfaces.
It is interestingly found that these molecules undertake a redox process
with a pair of well-defined reversible peaks in cyclic voltammograms
(CVs). The spectroscopic evidence shows a radical cation generated
with rising new Raman peaks related to parallel CC stretching of a
positively charged pyridyl ring. Furthermore, these electrochemically
charged bipyridine is also confirmed by electrochemical STM-BJ at
the single-molecule level, which displays a binary conductance switch
ratio of about 400% at the redox potentials. This present work offers
a molecular-level insight into the pyridine-mediated reaction process
and electron transport in RTILs.
Clarifying interfacial electronic effects on molecular adsorption is significant in many chemical and biochemical processes.H ere,w eu sed STM breaking junction and shellisolated nanoparticle-enhanced Raman spectroscopyt op robe electron transport and adsorption geometries of 4,4'-bipyridine (4,4'-BPY) at Au(111). Modifying the surface with 1-butyl-3methylimidazolium cation-containing ionic liquids (ILs) decreases surface electron density and stabilizes av ertical orientation of pyridine through nitrogen atom s-bond interactions,r esulting in uniform adsorption configurations for forming molecular junctions.Modulation from vertical, tilted, to flat, is achieved on adding water to ILs,l eading to an ew peak ascribed to CC stretching of adsorbed pyridyl ring and 316 %m odulation of single-molecule conductance.T he dihedral angle between adsorbed pyridyl ring and surface decreases with increasing surface electronic density,e nhancing electron donation from surface to pyridyl ring.
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