A two-dimensional molecular sieve has been realized. It consists of a host matrix of molecularly engineered building blocks self-assembled at the liquid-solid interface. The simultaneous size- and shape-dependent dynamics of different guest molecules is observed in situ, in real time with submolecular resolution using a scanning tunneling microscope both at the liquid-solid interface and under vacuum. The temperature-dependent dynamics reveals that the diffusion proceeds through thermally activated channeling between single-molecule surface cavities.

The temperature and concentration dependences of the self-assembly onto graphite from solution of a series of molecular building blocks able to form nanoporous structures are analyzed experimentally by in situ scanning tunneling microscopy. It is shown that the commonly observed coexistence of dense and nanoporous domains results from kinetic blockades rather than a thermodynamic equilibrium. The ripening can be favored by high densities of domain boundaries, which can be obtained by cooling the substrate before the nucleation and growth. Then ripening at higher-temperature yields large defect-free domains of a single structure. This thermodynamically stable structure can be either the dense or the nanoporous one, depending on the tecton concentration in the supernatant solution. A sharp phase transition from dense to honeycomb structures is observed at a critical concentration. This collective phenomenon is explained by introducing interactions between adsorbed molecules in the thermodynamic description of the whole system.

Self-assembly is a promising bottom-up route towards atomically precise fabrication of functional systems.[1] Nanoporous networks [2] that can host guest molecules [3,4] were obtained on metal surfaces under ultrahigh vacuum. Various supramolecular chemistry approaches have been applied [5][6][7][8][9] to obtain thermally [10,11] or chemically controlled [12,13] polymorphs. The spontaneous formation of patterns with hexagonal, [14] porous honeycomb, [15,16] or KagomØ [17] geometries has been also observed at the solution/solid interface. [18,19] The topologies, as well as the drastic structural changes often induced by minute changes in molecular structure [20] or solvent, [21] are usually explained a posteriori on the basis of molecular symmetry, molecule-substrate interactions, and moleculemolecule interactions. Interdigitation of alkyl chains is an example of the last-named [15,16,22,23] which is of practical interest since it is specific to the surface and does not occur in the bulk of the solution. Surprisingly, close-packed epitaxy of n-alkanes on highly ordered pyrolytic graphite (HOPG) [24][25][26] has not yet inspired the design of molecular linker exploiting this behavior.Hence, we designed a new molecular unit acting as a functional linking group able to form strong surface-assisted intermolecular "clips" which, by interdigitation, strictly mimic the atomically precise organization of n-alkanes on HOPG. It forms the basis of a design strategy which parallels polymer chemistry in that mono-, bi-, and trifunctional clipbearing building blocks form noncovalent surface dimers, polymers, and two-dimensional (2D) networks, respectively. We can then chemically steer the organization of these entities themselves at a higher supramolecular level.The adsorption of n-alkanes on HOPG results in the formation of close-packed 2D lamellae of parallel-aligned rectilinear chains, oriented along the h100i direction of graphite [19,25,26] according to the Groszek model [24] (Figure 1 A). Organization of the adsorbed monolayers is driven by two main factors: The first is the correspondence between the zigzag alternation of methylene groups and the h100i direction of HOPG, with a stabilization energy of about 64 meV per methylene group.[27] The second is the parallel packing of alkane molecules, which, besides steric hindrance, results from a stabilization energy between nearest chains 4.1 apart. From theoretical estimations, [28] we can infer 2D crystallization energies on the order of 20-25 meV per pair of facing methylene groups.

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.

Charge transfer (CT) is a fundamental and ubiquitous mechanism in biology, physics and chemistry. Here, we evidence that CT dynamics can be altered by multi-layered hyperbolic metamaterial (HMM) substrates. Taking triphenylene:perylene diimide dyad supramolecular self-assemblies as a model system, we reveal longer-lived CT states in the presence of HMM structures, with both charge separation and recombination characteristic times increased by factors of 2.4 and 1.7-that is, relative variations of 140 and 73%, respectively. To rationalize these experimental results in terms of driving force, we successfully introduce image dipole interactions in Marcus theory. The non-local effect herein demonstrated is directly linked to the number of metal-dielectric pairs, can be formalized in the dielectric permittivity, and is presented as a solid analogue to local solvent polarity effects. This model and extra PH3T:PC60BM results show the generality of this non-local phenomenon and that a wide range of kinetic tailoring opportunities can arise from substrate engineering. This work paves the way toward the design of artificial substrates to control CT dynamics of interest for applications in optoelectronics and chemistry.