On-Surface Photopolymerization - What Does the Surface Do?

Abstract

We attained the synthesis of mesoscale-ordered 2D polymers by the topochemical on-surface photopolymerization of fluorinated anthracene triptycene (fantrip) monomers. The underlying protocol is two-staged: (1) Self-assembly of the monomers into a photopolymerizable monolayer structure, where the photoactive anthracene moieties are face-to-face stacked; (2) cross-linking of the self-assembled monolayer into a covalent 2D polymer by photochemically excited [4+4] cycloadditions between the antiparallel aligned anthracene blades. Thereby, the long-range order attained in step (1) is transferred into the covalent state.Yet, the topochemical approach depends crucially on achieving the reactive monomer packing with the appropriate mutual alignment of the anthracene blades. For this initial self-assembly, the underlying surface plays a decisive role, which also extends to the photopolymerization.We show that the photoactive monolayer packing of fantrip monomers can be achieved on both alkane-passivated graphite and iodine-passivated Au(111) or Ag(111). Although the fantrip self-assembly appears essentially similar on these substrates, there are distinct differences in the subsequent photopolymerization. These can be rationalized by the photoexcitation of the substrate and the subsequent transfer of hot carriers to the molecular networks.Nat. Chem. 13, 730-736 (2021)Eur. J. Org. Chem. 2021, 5478–5490 (2021)Trends Chem. 4, 471-474 (2022)Angew. Chem. Int. Ed. 61, e202201044 (2022)