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The fascinating structural flexibility of porous polymers is highly attractive because it can result in optimized materials with specific host–guest interactions. Nevertheless, the fundamental mechanisms responsible for controlling the weak interactions of these hydrogen bond-rich networks—essential for developing smart task-specific materials used in recognition, capture, and sequestration processes—remain unexplored. Herein, by systematically comparing performance changes between poly(amic acid) (PAA)- and polycyclic imide (PI)-based porous polymers before and after NH3adsorption, the role of hydrogen bonds in conformational lability and responsiveness toward guest molecules is highlighted. By combining thermal gravimetric analysis with neutron spectroscopy supported by DFT calculations, we demonstrate that PAA’s chemical and physical stability is enhanced by the presence of stronger host–guest interactions. This observation also emphasizes the idea that efficient adsorption relies on having a high number of sites, upon which gas molecules can adsorb with greater affinity via strong hydrogen bonding interactions.

Amic acids, consisting of carboxylic acids and amides, are often utilized as intermediates that can further undergo a dehydration–cyclization step to yield polymeric cyclic imides. Compared with imide-based materials, the presence of Brønsted acidic groups and multiple hydrogen-bond donors and acceptors in materials incorporating amic acids opens up the possibility for a variety of host–guest interactions. Here we report a facile and catalyst-free synthesis of a Brønsted acidic porous poly(amic acid) (PAA) and present its NH3uptake properties using gas adsorption and breakthrough measurements. Simple addition of water as a cosolvent to a mixture of tetrakis(4-aminophenyl)methane and pyromellitic anhydride resulted in the formation of PAA in almost quantitative yield. Further mechanistic studies with model compounds revealed the importance of additive water to generate amic acid species selectively without forming cyclic imides at high temperatures. Gas adsorption isotherms and breakthrough curves obtained under dry and humid conditions demonstrate the enhanced NH3uptake in the case of PAA compared with the related polycyclic imide at both low and high pressures. Furthermore, the results of adsorption/desorption cycling experiments provide insights into the strength of the interaction between ammonia and the polymers.

MOFs on the move: A copper‐coordinated [2]pseudorotaxanate which reacts with zinc nitrate to form threefold interpenetrated networks retains most of its solution‐state chemistry, including its ability to undergo electronic switching of some of the copper(I) ions under redox control.

MOFs in Bewegung: Ein Kupfer‐koordiniertes [2]Pseudorotaxanat, das mit Zinknitrat zu einer dreifach verschlungenen Netzwerkstruktur reagiert, behält seine Lösungschemie weitgehend bei. So können z. B. Kupfer(I)‐Ionen unter Redoxkontrolle elektronisch geschaltet werden.

Something to remember: A rotaxane could be operated as a bistable memory element under kinetic control (see picture). Data was written on the molecule by an oxidation stimulus and locked by UV light irradiation. After the writing session, the oxidized species was reduced back to the original form without losing the written data for a few hours. Light irradiation also protects nonoxidized rotaxanes from accidental writing.

Bleibende Erinnerung: Ein Rotaxan konnte als bistabiles, kinetisch kontrollierbares Speicherelement betrieben werden (siehe Bild). Daten werden durch oxidativen Stimulus auf das Molekül geschrieben und mit UV‐Licht gesichert. Nach dem Schreiben werden die oxidierten Spezies wieder in die ursprüngliche Form reduziert, wobei die Daten einige Stunden erhalten bleiben. Bestrahlung schützt auch nicht‐oxidierte Rotaxane vor versehentlicher Beschriftung.

Ein redoxkontrollierbares bistabiles [2]Rotaxanwurde durch Templat‐ und Klickchemie synthetisiert. Mithilfe eines Elektronendonors werden unter Luftausschluss lichtausgelöste Schaltzyklen durch Radikalpaarbildungen zwischen der reduzierten Form von Cyclophan und der Bipyridinium‐Einheit durchlaufen. In Gegenwart von Luft (O2) werden die Wechselwirkungen durch Donor‐Akzeptor‐Ladungstransfer zurückgesetzt.

A redox‐controllable bistable [2]rotaxanehas been synthesized using templation and click chemistry. With assistance from a sacrificial electron donor, light‐triggered switching through numerous cycles can be initiated by radical‐pairing interactions between the reduced forms of the cyclophane and the bipyridinium unit in aqueous solution in the absence of air. In the presence of air (O2), the interactions are reset by donor–acceptor charge transfer.

Five donor–acceptor oligorotaxanes made up of dumbbells composed of tetraethylene glycol chains, interspersed with three and five 1,5‐dioxynaphthalene units, and terminated by 2,6‐diisopropylphenoxy stoppers, have been prepared by the threading of discrete numbers of cyclobis(paraquat‐p‐phenylene) rings, followed by a kinetically controlled stoppering protocol that relies on click chemistry. The well‐known copper(I)‐catalyzed alkyne–azide cycloaddition between azide functions placed at the ends of the polyether chains and alkyne‐bearing stopper precursors was employed during the final kinetically controlled template‐directed synthesis of the five oligorotaxanes, which were characterized subsequently by 1H NMR spectroscopy at low temperature (233 K) in deuterated acetonitrile. The secondary structures, as well as the conformations, of the five oligorotaxanes were unraveled by spectroscopic comparison with the dumbbell and ring components. By focusing attention on the changes in chemical shifts of some key probe protons, obtained from a wide range of low‐temperature spectra, a picture emerges of a high degree of folding within the thread protons of the dumbbells of four of the five oligorotaxanes—the fifth oligorotaxane represents a control compound in effect—brought about by a combination of CH⋅⋅⋅O and π–π stacking interactions between the π‐electron‐deficient bipyridinium units in the rings and the π‐electron‐rich 1,5‐dioxynaphthalene units and polyether chains in the dumbbells. The secondary structures of a foldamer‐like nature have received further support from a solid‐state superstructure of a related [3]pseudorotaxane and density functional calculations performed thereon.

Rotacatenanes are exotic molecular compounds that can be visualized as a unique combination of a [2]catenane and a [2]rotaxane, thereby combining both the circumrotation of the ring component (rotary motion) and the shuttling of the dumbbell component (translational motion) in one structure. Herein, we describe a strategy for the synthesis of a new switchable [3]rotacatenane and the investigation of its switching properties, which rely on the formation of tetrathiafulvalene (TTF) radical π‐dimer interactions—namely, the mixed‐valence state (TTF2)+.and the radical‐cation dimer state (TTF+.)2—under ambient conditions. A template‐directed approach, based on donor–acceptor interactions, has been developed, resulting in an improved yield of the key precursor [2]catenane, prior to rotacatenation. The nature of the binding between the [2]catenane and selected π‐electron‐rich templates has been elucidated by using X‐ray crystallography and UV/Vis spectroscopy as well as isothermal titration microcalorimetry. The multistate switching mechanism of the [3]rotacatenane has been demonstrated by cyclic voltammetry and EPR spectroscopy. Most notably, the radical‐cation dimer state (TTF+.)2has been shown to enter into an equilibrium by forming the co‐conformation in which the two 1,5‐dioxynaphthalene (DNP) units co‐occupy the cavity of tetracationic cyclophane, thus enforcing the separation of TTF radical‐cation dimer (TTF+.)2. The population ratio of this equilibrium state was found to be 1:1. We believe that this research demonstrates the power of constructing complex molecular machines using template‐directed protocols, enabling us to make the transition from simple molecular switches to their multistate variants for enhancing information storage in molecular electronic devices.

No Abstract

Außergewöhnlich langemolekulare Stützbalken mit mechanisch verzahnten Donor‐Akzeptor‐[2]Catenan‐Gruppen wurden ortsgenau und mit einheitlicher gegenseitiger Ausrichtung in ein dreidimensionales Metall‐organisches Gerüst eingebaut. Verzahnungsmotive finden sich sowohl in den molekularen Stützbalken als auch im gesamten Gerüst.

Einen lichtgesteuerten molekularen Schalterin Form eines bistabilen [2]Rotaxans, das viele Zyklen kontrollierbarer intramolekularer Bewegungen in Wasser durchläuft, beschreiben J. F. Stoddart et al. in der Zuschrift auf S. 6914 ff.Die Untersuchungen sind grundlegend für ein besseres Verständnis in Wasser operierender molekularer Schalter und die Möglichkeit zur Entwicklung integrierter nanobiochemischer Systeme für die Anwendung auf neuen anspruchsvollen Gebieten.

A light‐stimulated molecular switchin the form of a bistable [2]rotaxane, which undergoes controllable intramolecular motion through many cycles in water, is described by J. F. Stoddart and co‐workers in their Communication on page 6782 ff.The fundamental understanding of molecular switches that operate in water is improved and the possibility of developing integrated nanobiomechanical systems for applications in challenging arenas, such as molecular prosthetics, is opened up.

The International Year of Chemistry 2011…︁…︁is an initiative of the International Union of Pure and Applied Chemistry (IUPAC) and the United Nations Educational, Scientific, and Cultural Organization (UNESCO). Under the motto “Chemistry—our life, our future”, it is a worldwide celebration of the achievements of chemistry and its contributions to the well‐being of humankind. As part of our own contribution to the International Year of Chemistry, the cover of this special issue features a collage of chemistry from around the world. Going clockwise from the top left‐hand corner, the work featured is on amphiphilic lanthanide helicates by Claude Piguet, Emmanuel Terazzi, Jiri Mareda et al. (p. 184); on a multistate switchable [3]rotacatenane by J. Fraser Stoddart et al. (p. 213); on heuristic chemistry—addition reactions by Peter Schreiner et al. (p. 30); on steric, electronic, and secondary effects on the coordination chemistry of ionic phosphine ligands and the catalytic behavior of their metal complexes by Robertus J. M. Klein Gebbink et al. (p. 42); on the synthesis and structural features of 4,5‐disubstituted N,N′‐di‐tert‐alkyl imidazolium by Svetlana Polyakova, Ilya M. Lyapkalo et al. (p. 96); on luminescent cyclometalated dialkynylgold(III) complexes of 2‐phenylpyridine‐type derivatives with readily tunable emission properties by Vivian Wing‐Wah Yam et al. (p. 130); on recent developments in methodology for the direct oxyamination of olefins by Timothy J. Donohoe et al. (p. 58); and last but by no means least, on configurational and constitutional information storage by Nobel Prize winner, and co‐founder of the journal, Jean‐Marie Lehn et al. (p. 248).