Redox-Induced Orientation Change of a Self-Assembled Monolayer of 11-Ferrocenyl-1-undecanethiol on a Gold Electrode Studied by <i>in Situ</i> FT-IRRAS

Ye, Shen; Sato, Yukari; Uosaki, Kohei

doi:10.1021/la9700432

Cited by 129 publications

(197 citation statements)

References 52 publications

(105 reference statements)

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“…According to this interpretation, the hydrophilic carboxylate heads would reorient the hydrocarbon chain of the chemisorbed thiols by pulling them towards the solution. It should be pointed out that similar potential-induced reorientations have been proposed by Uosaki et al [27] and Burgess et al [28] to account for the changes brought into the IR spectrum of electroactive SAMs upon oxidizing their redox moieties. To obtain potentiostatic titration curves of the same monolayer under equilibrium conditions, we used as a reference the (nearly) neutral monolayer in contact with an acid solution of pH * 3.4 [29], and varied both potential and pH * according to the sequence illustrated in Figure 2.…”

Section: Resultssupporting

confidence: 71%

Potentiostatic infrared titration of 11-mercaptoundecanoic acid monolayers

Luque¹,

Cuesta²,

Calvente³

et al. 2014

Electrochemistry Communications

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In situ IR difference spectra of 11-mercaptoundecanoic acid (MUA) monolayers deposited on gold, and in the presence of a NaF solution in deuterated water, have been recorded as a function of both solution pH * and substrate's potential. IR spectra recorded under voltammetric conditions indicate that the potential-induced ionization of the monolayer is a slow process, involving a simultaneous rearrangement of the hydrocarbon chains, and that a significant population of carboxylic groups are not dissociated at positive potentials, even in the presence of a pH * 9 solution. Steep potentiostatic IR titration curves, consistent with a monolayer pKa = 4.3, are obtained at negative potentials. As the potential is made more positive, titration curves become lower, broader and are shifted towards more basic pHs, as would be expected when only a fraction of the carboxylic groups become ionized in the presence of less favorable interactions. Rather than acting directly on the electrostatic energy of the carboxylate groups, the electrode potential seems to control the ionization of the monolayer by attracting (or repelling) cations from the electrolyte and by reorienting the thiol head groups inside and outside the low permittivity layer of methylene chains.

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Section: Resultssupporting

confidence: 71%

Potentiostatic infrared titration of 11-mercaptoundecanoic acid monolayers

Luque¹,

Cuesta²,

Calvente³

et al. 2014

Electrochemistry Communications

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“…7 Finally, oxidation of the Fc moieties results in an orientational change which in turn results in a monolayer film thickness increase. 8 Although these studies have provided significant insight into the structure and electron-transfer processes of Fc-terminated SAMs there are still important issues to be resolved. Particularly, it is important to determine the electronic structure including work function changes induced by the electroactive SAMs.…”

Section: Introductionmentioning

confidence: 99%

Molecular and electronic structure of electroactive self-assembled monolayers

Leo

Llave

Scherlis

et al. 2013

The Journal of Chemical Physics

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Self-assembled monolayers (SAMs) containing electroactive functional groups are excellent model systems for the formation of electronic devices by self-assembly. In particular ferrocene-terminated alkanethiol SAMs have been extensively studied in the past. However, there are still open questions related with their electronic structure including the influence of the ferrocene group in the SAMinduced work function changes of the underlying metal. We have thus carried out a thorough experimental and theoretical investigation in order to determine the molecular and electronic structure of ferrocene-terminated alkanethiol SAMs on Au surfaces. In agreement with previous studies we found that the Fc-containing alkanethiol molecules adsorb forming a thiolate bond with the Au surface with a molecular geometry 30• tilted with respect to the surface normal. Measured surface coverages indicate the formation of a compact monolayer. We found for the first time that the ferrocene group has little influence on the observed work function decrease which is largely determined by the alkanethiol. Furthermore, the ferrocene moiety lies 14 Å above the metal surface covalently bonded to the alkanethiol SAM and its HOMO is located at −1.6 eV below the Fermi level. Our results provide new valuable insight into the molecular and electronic structure of electroactive SAMs which are of fundamental importance in the field of molecular electronics.

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“…Ye et al attributed the increase in thickness to changes in tilt angles of alkyl chains caused by oxidation of the terminal ferrocenyl group. 8 Viana et al claimed that conformational change of the terminal ferrocenyl group is dominant for the thickness change.…”

Section: Structure Of Ion Pairing Upon Oxidation Of Ferrocenyl Groupsmentioning

confidence: 99%

“…[1][2][3][4][5] The terminal Fc groups exhibit a definite redox reaction whose dependences on electrolyte solution and alkyl chain length have been studied mainly by cyclic voltammetry (CV). On the other hand, several in situ techniques including infrared reflection adsorption spectroscopy (IRRAS), [6][7][8][9] quartz crystal microbalance (QCM), 9-11 ellipsometry 12,13 and subtractively normalized interfacial Fourier transform infrared spectroscopy (SNIFTIRS), 14 have been employed to elucidate property changes of the Fc-terminated SAMs caused by oxidation and reduction of the monolayer. Despite the simplicity of the reaction itself, the reaction changes several properties of the layer including layer thickness, refractive index and hydrophilicity.…”

Section: Introductionmentioning

confidence: 99%