Versatile bottom-up construction of diverse macromolecules on a surface observed by scanning tunneling microscopy.

The heterocoupling of organic building blocks to give complex multicomponent macromolecules directly at a surface holds the key to creating advanced molecular devices. While "on-surface" synthesis with prefunctionalized molecules has recently led to specific one- and two- component products, a central challenge is to discover universal connection strategies that are applicable to a wide range of molecules. Here, we show that direct activation of C-H bonds intrinsic to π-functional molecules is a highly generic route for connecting different building blocks on a copper surface. Scanning tunneling microscopy (STM) reveals that covalent π-functional macromolecular heterostructures, displaying diverse compositions, structures and topologies, are created with ease from seven distinct building blocks (including porphyrins, pentacene and perylene). By exploiting differences in C-H bond reactivity in the deposition and heating protocols we also demonstrate controlled synthesis of specific products, such as block copolymers. Further, the symmetry and geometry of the molecules and the surface also play a critical role in determining the outcome of the covalent bond forming reactions. Our "pick-mix-and-link" strategy opens up the capability to generate libraries of multivariate macromolecules directly at a surface, which in conjunction with nanoscale probing techniques could accelerate the discovery of functional interfaces.