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  1. Crystals composed of photoreactive molecules represent a new class of photomechanical materials with the potential to generate large forces on fast timescales. An example is the photodimerization of 9- tert -butyl-anthracene ester ( 9TBAE ) in molecular crystal nanorods that leads to an average elongation of 8%. Previous work showed that this expansion results from the formation of a metastable crystalline product. In this article, it is shown how a novel combination of ensemble oriented-crystal solid-state NMR, X-ray diffraction, and first principles computational modeling can be used to establish the absolute unit cell orientations relative to the shape change, revealing the atomic-resolution mechanism for the photomechanical response and enabling the construction of a model that predicts an elongation of 7.4%, in good agreement with the experimental value. According to this model, the nanorod expansion does not result from an overall change in the volume of the unit cell, but rather from an anisotropic rearrangement of the molecular contents. The ability to understand quantitatively how molecular-level photochemistry generates mechanical displacements allows us to predict that the expansion could be tuned from +9% to −9.5% by controlling the initial orientation of the unit cell with respect to the nanorod axis. This applicationmore »of NMR-assisted crystallography provides a new tool capable of tying the atomic-level structural rearrangement of the reacting molecular species to the mechanical response of a nanostructured sample.« less
  2. A spacious Fe( ii )-iminopyridine self-assembled cage complex can catalyze the oxidative dimerization of alkanethiols, with air as stoichiometric oxidant. The reaction is aided by selective molecular recognition of the reactants, and the active catalyst is derived from the Fe( ii ) centers that provide the structural vertices of the host. The host is even capable of size-selective oxidation and can discriminate between alkanethiols of identical reactivity, based solely on size.
  3. This Account describes our efforts over the last decade to synthesize self-assembled metal–ligand cage complexes that display reactive functional groups on their interiors. This journey has taken us down a variety of research avenues, including studying the mechanism of reversible self-assembly, analyzing ligand self-sorting properties, post-assembly reactivity, molecular recognition, and binding studies, and finally reactivity and catalysis. Each of these individual topics are discussed here, as are the lessons learned along the way and the future research outlook. These self-assembled hosts are the closest mimics of enzymes to date, as they are capable of size- and shape-selective molecular recognition, substrate activation and turnover, as well as showing less common ‘biomimetic’ properties such as the ability to employ cofactors in reactivity, and alter the prevailing mechanism of the catalyzed reactions. 1 Introduction 2 Paddlewheels and Self-Sorting Behavior 3 First-Row Transition-Metal-Mediated Assembly: Sorting and Stereochemical Control 4 Post-Assembly Reactivity 5 Molecular Recognition and Catalysis 6 Conclusions and Outlook