Cleaning up after the Party: Removing the Byproducts of On-Surface Ullmann Coupling

Ullmann coupling is one of the most frequently employed methodologies for producing π-conjugated surface-confined polymers. One unfortunate side product of the reaction is the creation of metal halide islands formed from liberated halogen atoms. Following the coupling reaction, these halide islands can account for a large proportion of the substrate surface area and thus inhibit domain growth and effectively poison the catalyst. Here, we describe an efficient and reliable methodology for removing the halogen byproduct at room temperature by exposure to a beam of atomic hydrogen; this action removes the halogen atoms in a matter of minutes, with minimal impact to the polymer structure. We also find that it is possible under certain circumstances to preserve the pre-exposure epitaxy after removal of the halogen. This finding provides a convenient and straightforward technique for addressing the most often-cited drawback of the on-surface Ullman coupling methodology and provides access to a previously inaccessible parameter space for these types of experiments.