Monitoring the On-Surface Boronic Acid Condensation Process at the Nanoscale Using Tip-Enhanced Raman Spectroscopy

The on-surface condensation of boronic acids is a key step in fabricating functional interfaces with tailored properties; yet, a clear understanding of the molecular structural transformations involved remains a significant challenge. Here, we directly monitor the condensation reaction in a self-assembled monolayer of 4-mercaptophenylboronic acid (MPBA) on Au(111) using tip-enhanced Raman spectroscopy (TERS). The structural evolution in the MPBA adlayer is tracked via the emergence of new peaks, blue shifts, and intensity changes in characteristic Raman bands. Hyperspectral TERS imaging provides comprehensive insight into molecular transformations, including B-O-B bond formation, increased molecular constraints, and an evolution in molecular orientation. Furthermore, density functional theory simulations confirm that the boroxine trimer is the primary product of the on-surface condensation reaction. This study provides significant insights into on-surface boronic acid condensation chemistry for the rational design of functionalized surfaces with targeted chemical properties.