Molecule-by-molecule positioning using template-guided self-assembly

Full text: Achieving precise control of molecular self-assembly to form designed three-dimensional (3D) structures is a major goal in nanoscale science and technology. Using scanning tunnelling microscopy and density functional theory calculations, we have investigated the use of a single-atom-thick 2D covalent organic framework (COF-1) to template solution processed guest molecules. This versatile approach can be used to trap and organize molecules at the solution/solid interface and in the subsequently obtained dried films. The molecular adsorption geometries depend on the solvent used for processing, and through the use of different solvents different (pseudo)polymorphs can be obtained. The transition from two-dimensional to three-dimensional molecular films has been observed, and indicates that these nanoscale COF-1 templates may enable novel packing geometries for device applications. The approach can also be used to pattern molecules with intrinsic barriers for forming periodic lattices, such as those with five-fold symmetry, demonstrating that monolayer templates may allow molecules designed for function, rather than crystallization into regular lattices, to be used in applications where crystallinity is desirable. (author)