TY - JOUR

T1 - Gold-carbonyl group interactions in the electrochemistry of anthraquinone thiols self-assembled on Au(111)-surfaces

AU - Wagner, Michal

AU - Qvortrup, Katrine

AU - Grier, Katja E.

AU - Ottosen, Mikkel

AU - Petersen, Jonas

AU - Tanner, D

AU - Ulstrup, Jens

AU - Zhang, Jingdong

PY - 2019

Y1 - 2019

N2 - New anthraquinone derivatives with either a single or two thiol groups (AQ1 and AQ2) were synthesized and immobilized in self-assembled monolayers (SAMs) on Au(111) electrodes via Au-S bonds. The resultant AQ1- and AQ2-SAMs were studied by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), which enabled mapping of the gold-carbonyl group interactions and other dynamics in the Au-S bound molecular framework. Understanding of these interactions is important for research on thiol-coated gold nanoclusters, since I) anthraquinone derivatives are a major compound family for providing desired redox functionality in multifarious assays or devices, and II) the gold-carbonyl interactions can strongly affect anthraquinone electrochemistry. Based on equivalent circuit analysis, it was found that there is a significant rise in polarization resistance (related to SAM structural reorganization) at potentials that can be attributed to the quinone/semi-quinone interconversion. The equivalent circuit model was validated by calculation of pseudocapacitance for quinone-to-hydroquinone interconversion, in good agreement with the values derived from CV. The EIS and CV patterns obtained provide consistent evidence for two different ECEC (i.e. proton-controlled ET steps, PCET) pathways in AQ1- and AQ2-SAMs. Notably, it was found that the formal reorganization (free) energies obtained for the elementary PCET steps are unexpectedly small for both SAMs studied. This anomaly suggests high layer rigidity and recumbent molecular orientation on gold surfaces, especially for the AQ2-SAMs. The results strongly indicate that gold-carbonyl group interactions can be controlled by favorable structural organization of anthraquinone-based molecules on gold surfaces.

AB - New anthraquinone derivatives with either a single or two thiol groups (AQ1 and AQ2) were synthesized and immobilized in self-assembled monolayers (SAMs) on Au(111) electrodes via Au-S bonds. The resultant AQ1- and AQ2-SAMs were studied by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), which enabled mapping of the gold-carbonyl group interactions and other dynamics in the Au-S bound molecular framework. Understanding of these interactions is important for research on thiol-coated gold nanoclusters, since I) anthraquinone derivatives are a major compound family for providing desired redox functionality in multifarious assays or devices, and II) the gold-carbonyl interactions can strongly affect anthraquinone electrochemistry. Based on equivalent circuit analysis, it was found that there is a significant rise in polarization resistance (related to SAM structural reorganization) at potentials that can be attributed to the quinone/semi-quinone interconversion. The equivalent circuit model was validated by calculation of pseudocapacitance for quinone-to-hydroquinone interconversion, in good agreement with the values derived from CV. The EIS and CV patterns obtained provide consistent evidence for two different ECEC (i.e. proton-controlled ET steps, PCET) pathways in AQ1- and AQ2-SAMs. Notably, it was found that the formal reorganization (free) energies obtained for the elementary PCET steps are unexpectedly small for both SAMs studied. This anomaly suggests high layer rigidity and recumbent molecular orientation on gold surfaces, especially for the AQ2-SAMs. The results strongly indicate that gold-carbonyl group interactions can be controlled by favorable structural organization of anthraquinone-based molecules on gold surfaces.

U2 - 10.1039/C9SC00061E

DO - 10.1039/C9SC00061E

M3 - Journal article

SP - 3927

EP - 3936

JO - Chemical Science

JF - Chemical Science

SN - 2041-6520

IS - 14

ER -