Sum frequency generation imaging of microcontact-printed monolayers derived from aliphatic dithiocarboxylic acids: Contrast based on terminal-group orientation

The results of imaging mu CP printed monolayers using sum frequency generation vibrational spectroscopy are presented, where the image contrast is based on the orientation of the terminal methyl groups. The printed regions contain thiols with 16 carbon atoms (even), and the backfilled regions contain 17 carbon atoms (odd). In the odd/even effect, the terminal group alternates its orientation as the number methylene group changes from even to odd. On the basis of this result, SFG imaging microscopy (SFGIM) is used to image the C16 and C17 regions where the difference is based on the orientation of the terminal methyl group. Furthermore, we compared the patterns formed by C16/C17 n-alkanethiols and C16/C17 aliphatic dithiocarboxylic acids. We find that the dithiocarboxylic acids form much-better patterns where the degree of mixing between the stamped and backfilled regions is reduced compared to the n-alkanethiols. Furthermore, this results shows that SFGIM is a useful technique to visualize monolayers based not only on the chemical functionality but also on the surface orientation of the adsorbates.