A nanoengineered surface able to grab selected molecules and further sort them according to their size and shape by diffusion through surface molecular sieves is realized. It consists of a customized self-assembled network of supramolecular cavities linked by channels. The comparison of the temperature-dependent hopping dynamics of various guest molecules (arrows in figure indicate their hopping between neighboring cavities; figure width: 7.7 nm) reveals the physical mechanisms of the involved processes.