Excitation wavelength-dependent multi-coloured and white-light emissive pyrene-based hydrazones: suppression of Kasha's rule.

Multi-coloured and white-light emissions from pyrene-based hydrazones are described. They exhibit excitation wavelength-dependent emissions in solution due to the suppression of Kasha's rule. Interestingly, in dimethylformamide, 1-3 emit light that covers all the regions of primary colours as a function of excitation wavelength, and 1 and 2 emit white light (λex = 420 nm) in isopropanol.

Carbohydrate recognition using metal-ligand assemblies.

Carbohydrate-binding proteins, known as lectins, play a wide range of vital roles in cellular and pathological processes. Mimicking lectins to achieve specific molecular recognition of carbohydrates in organic and aqueous media using artificial receptors is challenging due to the synthetic hurdles of receptors and structural similarities between sugars. Carbohydrate recognition using non-covalent interactions remains a vast topic. This review summarises the recognition of carbohydrates using metal-ligand assemblies, including metallosupramolecules, macrocycles, and cages. It also highlights the challenges and future directions in the field.

Circularly Polarized Luminescence in a Möbius Helicene Carbon Nanohoop.

We present the first helicene carbon nanoohop that integrates a [6]helicene into [7]cycloparaphenylene. The [6]helicene endows the helicene carbon nanohoop with chiroptical properties and configurational stability typical for higher helicenes, while the radially conjugated seven para-phenylenes largely determine the optoelectronic properties. The structure of the helicene carbon nanoohop was unambiguously characterized by NMR, MS and X-ray analysis that revealed that it possesses a topology of a Möbius strip in the solid state and in solution. The chirality transfers from the [6]helicene to the para-phenylenes and leads to a pronounced circular dichroism and bright circularly polarized luminescence, which is affected by the structural topology of the nanohoop.

A Switchable Catalyst Duo for Acyl Transfer Proximity Catalysis and Regulation of Substrate Selectivity.

Enzymes are encoded with a gamut of information to catalyze a highly selective transformation by selecting the proper reactants from an intricate mixture of constituents. Mimicking biological machinery, two switchable catalysts with differently sized cavities and allosteric control are conceived that allow complementary size-selective acyl transfer in an on/off manner by modulating the effective local concentration of the substrates. Selective activation of one of two catalysts in a mixture of reactants of similar reactivity enabled upregulation of the desired product.

Reversible Multicomponent AND Gate Triggered by Stoichiometric Chemical Pulses Commands the Self-Assembly and Actuation of Catalytic Machinery.

The present work demonstrates the operation of a reversible supramolecular gate, i.e., an ensemble of various components linked by chemical communication, which is triggered by stoichiometric chemical inputs and by obeying the AND truth table delivers a stoichiometric chemical signal. The output triggers a series of events that finally set up a catalytic process. In detail, a three-component AND gate, composed of two distinct nanoswitches, a copper-loaded and an unloaded one {= state (0,0)}, was actuated with stoichiometric amounts of two inputs (IN-1 = Zn2+, IN-2 = Hg2+) generating copper(I) ions as output in state (1,1). The utility of this information processing was highlighted by using the copper(I) output for triggering the self-assembly of the four-component rotor ROT-2 through metal translocation. In the presence of suitable reactants, ROT-2 acted as a catalytic machinery catalyzing a click reaction (= signal amplification). Verification of the functioning of the AND gate in a mixture of 12 components was thus accomplished by monitoring formation of the click product. Due to the stoichiometric design, the gate was reset to state (0,0) by adding hexacyclen and reactivated by adding inputs IN-1 and IN-2 alike in the first cycle.

Three-state switching in a double-pole change-over nanoswitch controlled by redox-dependent self-sorting.

The four-arm nanomechanical switch 1 with four different terminals exhibits two switching arms (contacts A and D) and two distinct stations for binding (contacts B and C). In switching State I, the azaterpyridine arm is intramolecularly coordinated to a zinc(ii) porphyrin station (connection A ↔ B) while contact D (a ferrocenylbipyridine unit) and contact C (phenanthroline) remain disconnected. After addition of copper(i) ions (State II) both connections A ↔ B and C ↔ D are established. Upon one-electron oxidation, double-pole change-over switching cleaves both connections A ↔ B & C ↔ D and establishes the new connection A ↔ C (State III). Fully reversible three-state switching (State I → State II → State III → State II → State I) was achieved by adding appropriate chemical and redox stimuli.

Selective detection of DABCO using a supramolecular interconversion as fluorescence reporter.

The quantitative double self-sorting between the three-component rectangle [Cu4(1)2(2)2]4+ and the four-component sandwich complex [Cu2(1)(2)(4)]2+ is triggered by inclusion and release of DABCO (4). The fully reversible and clean switching between two multicomponent supramolecular architectures can be monitored by fluorescence changes at the zinc porphyrin sites. The structural changes are accompanied by a huge spatial contraction/expansion of the zinc porphyrin-zinc porphyrin distances that change from 31.2/38.8 Å to 6.6 Å and back. The supramolecular interconversion was used for the highly selective detection of DABCO in a mixture of other similar compounds.

A high-speed network of nanoswitches for on/off control of catalysis.

NetState I of the communication-catalysis protocol is defined by a 1 : 1 mixture of the nanoswitches [Cu(1)]+ and 2. Upon one-electron oxidation at the ferrocenyl unit of the switch [Cu(1)]+, copper(i) ions are released that after translocation toggle nanoswitch 2 → [Cu(2)]+ (NetState II) within 4 min. NetState I was fully reset within 1 min by reduction of 1+ → 1. Running this redox-triggered switching protocol in the presence of 4-nitrobenzaldehyde, diethyl malonate and piperidine (catalyst) allows toggling of a catalyzed Knoevenagel addition from ON to OFF and back to ON.

Five-component trigonal nanoprism with six dynamic corners.

The metallo-supramolecular trigonal prism P is based on five different components and three unlike dynamic coordination motifs: the heteroleptic phenanthroline-terpyridine complex [Zn(1)(4)]2+ (HETTAP), the heteroleptic phenanthroline-pyridine complex [Cu(2)(5A)]+ (HETPYP-I), and the pyridine → zinc(ii)-porphyrin interaction.

Five-State Rotary Nanoswitch.

In our quest to develop artificial multistate devices, we synthesized the nanomechanical switch 1 that is characterized by a tetrahedral core equipped with four pending arms. The rotary arm with its azaterpyridine terminal is intramolecularly coordinated to a zinc(II) porphyrin station that is the terminus of another arm in 1. The two other arms carry identical sterically shielded phenanthroline stations. The 2-fold alternate addition of a copper(I) ion and [1,10]-phenanthroline (1 equiv each) results in the formation of five different switching states (State I→ State II→ State III→ State IV→ State V → State I), which force the toggling arm to move back and forth between the zinc(II) porphyrin and phenanthroline stations separated by a distance of 25 Å. All switching states constitute clean single species, except for State III, and thus are fully characterized by spectroscopic methods and elemental analysis. Finally, the initial state of nanoswitch was reset by addition of cyclam for complete removal of the copper(I) ions.

A Metalloregulated Four-State Nanoswitch Controls Two-Step Sequential Catalysis in an Eleven-Component System.

The nanomechanical switch 1 with its three orthogonal binding motifs-the zinc(II) porphyrin, azaterpyridine, and shielded phenanthroline binding station-is quantitatively and reversibly toggled back and forth between four different switching states by means of addition and removal of appropriate metal-ion inputs. Two of the four switching stages are able to initiate catalytic transformations (ON1, ON2), while the two others shut down any reaction (OFF1, OFF2). Thus, in a cyclic four-state switching process the sequential transformation A+B+C→AB+C→ABC can be controlled, which proceeds stepwise along the switching states OFF1→ON1 (click reaction: A+B→AB)→OFF2→ON2 (Michael addition: AB+C→ABC)→OFF1. Two consecutive cycles of the sequential catalysis were realized without loss in activity in a reaction system with eleven different components.

A molecular shuttle driven by fullerene radical-anion recognition.

We describe a electrochemically driven molecular shuttle, in which shuttling takes place by means of fullerene radical-anion recognition that results in a very low operation potential (E(1/2) =-0.580 V vs. decamethylferrocene). This has been achieved by introducing positive charges on the macrocycle, which strengthen the existing π-π interactions between the macrocycle and the electrogenerated fullerene radical anion by means of an electrostatic component. In addition, the synthesis of such a molecular shuttle has been accomplished by developing a new synthetic approach that exploits the controlled translocation of the macrocycle as a selective protecting group.