Strong Hydrogen Bonds at the Interface between Proton-Donating and -Accepting Self-Assembled Monolayers on Au(111)

Abstract

Hydrogen-bonding heterogeneous bilayers on substrates have been studied as a base for new functions of molecular adlayers by means of atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), infrared reflection absorption spectroscopy (IRAS), and density functional theory (DFT) calculations. Here, we report the formation of the catechol-fused bis(methylthio)tetrathiafulvalene (HCat-BMT-TTF) adlayer hydrogen bonding with an imidazole-terminated alkanethiolate self-assembled monolayer (Im-SAM) on Au(111). The heterogeneous bilayer is realized by sequential two-step immersions in solutions for the individual Im-SAM and HCat-BMT-TTF adlayer formations. In the measurements by AFM, a grained HCat-BMT-TTF adlayer on Im-SAM is revealed. The coverage and the chemical states of HCat-BMT-TTF on Im-SAM are specified by XPS. On the vibrational spectrum measured by IRAS, the strong hydrogen bonds between HCat-BMT-TTF and Im-SAM are characterized by the remarkably red-shifted OH stretching mode at 3140 cm, which is much lower than that for hydrogen-bonding water (typically ∼3300 cm). The OH stretching mode frequency and the adsorption strength for the HCat-BMT-TTF molecule hydrogen bonding with imidazole groups are quantitatively examined on the basis of DFT calculations.

Action of silicic acid derived from sodium silicate precursor toward improving performances of porous gelatin membrane

“…And the peaks at ~399.6 and ~401.0 eV were corresponding to C─NH─C bond and ─NH 2 bond, respectively. These values are in good agreement with that report in previous literature . That is, the imino N is at ~399.5 eV and the amino N is at 401.0–402.0 eV.…”

Direct Evidence of Interfacial Hydrogen Bonding in Proton-Electron Concerted 2D Organic Bilayer on Au Substrate

“…This indicates that the H2Cat-BMT-TTF grain consists of a single molecular layer. Note that small grains of similar diameter were also observed by AFM at room temperature in our previous study [10]. In this study, the high-resolution STM image at liquid N2 temperature further reveals that the small grains contain fine protrusions, which are separated by 1−2 nm [ Figure 2(b)].…”

“…Secondly, the Im-SAM/Au surface was immersed in a deoxygenated chloroform solution containing 1 mM of the synthesized H2Cat-BMT-TTF [11] for more than 20 h. All immersion processes were carried out under dry N2 atmosphere in a glove box at room temperature. Further details of sample preparation can be found in our previous publication [10].…”

“…It should be noted that H2Cat-BMT-TTF molecules do not cover the whole Im-SAM/Au surface. The coverage of H2Cat-BMT-TTF was estimated to be approximately 0.4 ML using XPS in our previous study [10]; 1 ML was defined as the saturation coverage of Im-SAM. The formation of 2D grains of H2Cat-BMT-TTF with the limited coverage is probably due to a steric hindrance among H2Cat-BMT-TTF molecules.…”

“…As the H + donor molecular layer, we chose catechol-fused bis(methylthio)tetrathiafulvalene (H2Cat-BMT-TTF) [ Figure 1 , which was examined by various experimental techniques, including scanning tunneling microscopy (STM), infrared reflection absorption spectroscopy (IRAS), and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. In our previous study [10], the same 2D organic bilayer was investigated by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), IRAS, and density functional theory calculations. With the additional experimental data from the present study, direct evidence of H-bonding in a 2D organic bilayer can be obtained.…”