Surface-Mounted Metal-Organic Frameworks: Crystalline and Porous Molecular Assemblies for Fundamental Insights and Advanced Applications

Metal-organic frameworks (MOFs) are crystalline coordination polymers, assembled from inorganic nodes connected by organic linker molecules. An enormous surface area, huge compositional variety, regular structure, and favorable mechanical properties are among their outstanding properties. Monolithic MOF thin films, i.e., surface-mounted metal-organic frameworks (SURMOFs), with high degree of structural order and adjustable defect density, can be prepared on solid substrates using layer-by-layer techniques. Recent studies where SURMOFs served as model systems for quantitative studies of molecular interactions in porous media, including diffusion, are reviewed. Moreover, SURMOFs are ideally suited for the incorporation of photoactive molecules as well as to study electrical transport through crystalline molecular assemblies. Recent work has demonstrated that the realization of crystalline chromophore assemblies via the SURMOF approach allows the study of fundamental aspects of exciton transport, exciton channeling, and photon upconversion at internal interfaces in organic semiconductor materials. Due to their crystalline nature, MOF materials are well suited for quantitative comparisons with theoretical results; especially, since defect densities and types can be characterized and varied in a straightforward fashion. The active role of these nanoporous films in advanced applications, like for remote-controlled release of molecules, membranes with photoswitchable selectivity, and ion-conductors with adjustable conductivity, are also emphasized.