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.