On-surface polymerization is a promising technique to prepare organic functional nanomaterials that are challenging to synthesize in solution, but it is typically used on metal substrates, which play a catalytic role. Previous examples on insulating surfaces have involved intermediate self-assembled structures, which face high barriers to diffusion, or annealing to higher temperatures, which generally causes rapid dewetting and desorption of the monomers. Here we report the photoinitiated radical polymerization, initiated from a two-dimensional gas phase, of a dimaleimide monomer on an insulating KCl surface. Polymer fibres up to 1 μm long are formed through chain-like rather than step-like growth. Interactions between potassium cations and the dimaleimide's oxygen atoms facilitate the propagation of the polymer fibres along a preferred axis of the substrate over long distances. Density functional theory calculations, non-contact atomic force microscopy imaging and manipulations at room temperature were used to explore the initiation and propagation processes, as well as the structure and stability of the resulting one-dimensional polymer fibres.

Achieving control over formation of molecular films on insulating substrates is important for designing novel 2D functional materials and devices. To study the main factors governing successful control, organic molecules with interchangeable polar functional groups, a variable length aromatic body, and flexible hydrocarbon chains are designed, synthesized and then deposited on the (001) surfaces of bulk sodium chloride, potassium chloride, and rubidium chloride. The deposited structures are imaged using noncontact atomic force microscopy and modeled using density functional theory. The results show that it is possible to form large‐scale, highly ordered, 2D, porous molecular domains (>104 pores), which are stable at room temperature, and to control the size of the 2D pores. Alternatively, it is possible to form line structures or droplets (through molecular dewetting) by altering the molecular structure or changing the substrate lattice constant. Theoretical calculations explain the balance of the molecule–molecule and molecule–surface interactions and the structure and thermodynamic stability of the grown films.