Thermal- vs Light-Induced On-Surface Polymerization

Abstract

On-surface polymerization is a powerful bottom-up approach that allows for the growth of covalent architectures with defined properties using the two-dimensional confinement of a highly defined single-crystal surface. Thermal heating is the preferred approach to initiate the reaction, often via cleavage of halogen substituents from the molecular building blocks. Light represents an alternative stimulus but has, thus far, only rarely been used. Here, we present a direct comparison of on-surface polymerization of dibromo-anthracene molecules, induced either thermally or by light, and study the differences between the two approaches. Insight is obtained by a combination of scanning tunneling microscopy, locally studying the polymer shape and size, and X-ray photoelectron spectroscopy, which identifies bond formation by averaging over large surface areas. While the polymer length increases slowly with the sample heating temperature, illumination promotes only the formation of short covalent structures, independent of the duration of light exposure. Moreover, irradiation with UV light at different sample temperatures highlights the important role of molecular diffusion across the surface.

Initial Coupling and Reaction Progression of Directly Deposited Biradical Graphene Nanoribbon Monomers on Iodine-Passivated Versus Pristine Ag(111)

“…Instead of covalent chains, we observed the formation of short organometallic segments. This indicates low mobility of the radicals on the bare metal surface at room temperature, as similarly suggested by experiments with ultraviolet light-induced dehalo-genation [49]. This may also explain formation of organometallic intermediates rather than the covalent products, where bonding with Ag atoms provided by the free adatom gas is kinetically preferred.…”

On-Surface Two-Dimensional Polymerization: Advances, Challenges, and Prospects

“…As an auspicious stimulus for covalent synthesis, light irradiation can induce polymerization reactions at room temperature . Therefore, the long-range ordered molecular assembly can survive during photochemical reactions and benefit the formation of high-quality 2DPs . For instance, Lackinger et al reported the on-surface photopolymerization of 2DP ordered on the mesoscale.…”

Solvent Co-adsorption Changing the Type of Halogen-Based Bonds Associated with the Position of Bromine Substituents Revealed by Scanning Tunneling Microscopy

“…Two-dimensional (2D) molecular self-assembly is of great significance for building preprogrammed structures and patterns on such a scale using the bottom–top approach . The formation of 2D self-assembled nanostructures is a result of thermodynamic equilibrium, affected by temperature, − molecular chemical structure, − solvent, − solution concentration, − substrate, , and so on. These factors essentially change the intermolecular interaction and/or molecule–substrate interaction of self-assembly adlayers.…”