Surface Structure and Composition of Thiophene-Bearing Monolayers

Abstract

We have used X-ray photoelectron spectroscopy and external reflectance Fourier transform infrared spectroscopy (ER-FTIR) to investigate the structure and composition of mixed monolayers made from n-alkyl chains and ω-(3-thienyl)alkyltrichlorosilanes. Monolayers made from 11-(3-thienyl)undecyltrichlorosilane (3TUTS) and undecyltrichlorosilane (UTS) and also from 16-(3-thienyl)hexadecyltrichlorosilane (3THTS) and hexadecyltrichlorosilane (HTS) were examined. ER-FTIR indicates that mixed monolayers made from 3TUTS/UTS and 3THTS/HTS form nearly liquidlike monolayers on indium tin oxide (ITO) substrates. The pendant thiophene group is located at the periphery of the self-assembled monolayer (SAM), and it appears to be oriented along the SAM. Both spectroscopic techniques suggest that during assembly of mixed monolayers, the ω-(3-thienyl)alkyltrichlorosilane species preferentially adsorbs, leading to a monolayer enriched in the thiophene-capped component. The information resulting from these studies will be generally useful for tailoring the structure and properties of electroactive monolayers on ITO substrates.

Detection of 2,4-Dinitrotoluene (DNT) as a Model System for Nitroaromatic Compounds via Molecularly Imprinted Short-Alkyl-Chain SAMs

“…This indicates the preferential and specific association of DNT to the imprinted monolayer network. Such an increase in the chargetransfer resistance may also be due to the electrostatic repulsion in the presence of the NO 2 groups of DNT with the negatively charged Fe(CN) 6 3À/4À . Moreover, the noted increase in the radius of the semicircle is a function of the concentration of DNT as shown in Figure 7.…”

“…However, Warburg impedance was more pronounced with the MIM film as the phase angle shifted to approximately 45°. The binding trend of DNT to the MIM film was studied with a redox probe, K 3 Fe-(CN) 6 . It was shown that the radius of the semicircle, which represents the charge-transfer phenomenon, tends to increase with increasing concentrations of the incorporated DNT.…”

“…For EIS indirect sensing, a 5 mM K 3 Fe(CN) 6 probe was used to obtain quantifiable impedance spectra and minimize the "repeated measurement-related" R ct increase. An experiment using NIM was also performed to validate the assumption that changes in the charge-transfer resistance were due to the binding of DNT to the butanethiol monolayer.…”

“…A method to improve the sensitivity of MIP-based chemical sensors is to chemically modify a surface with organic molecule adsorbates. 6 Self-assembled monolayers (SAMs) are widely known to provide uniformly structured surfaces and allow the incorporation of functional groups that alter the surface's wetting, 7 frictional, 8 adhesive, 9 or recognition 10 properties. Examples include organothiols on metal (gold, silver, and copper) and organosilanes, organophosphates, and acids on metal oxide (ITO, alumina, and steel) substrates.…”

“…A method to improve the sensitivity of MIP-based chemical sensors is to chemically modify a surface with organic molecule adsorbates . Self-assembled monolayers (SAMs) are widely known to provide uniformly structured surfaces and allow the incorporation of functional groups that alter the surface’s wetting, frictional, adhesive, or recognition properties.…”