Cation‐Driven Self‐Assembly of a Gold(I)‐Based Metallo‐Tweezer

Clippane: A Mechanically Interlocked Molecule (MIM) Based on Molecular Tweezers

In this study we report the preparation of a new mechanically interlocked molecule formed by the self-aggregation of two metallotweezers composed by two pyrene-imidazolylidene gold(I) arms and a pyridine-centered pentacyclic bis-alkynyl linker. The mechanically interlocked nature of this molecule arises from the presence of the bulky tert-butyl groups attached to the sides of the pyrene moieties of the arms of the tweezer, which act as stoppers avoiding the dissociation of the self-aggregated metallotweezer dimer once it is formed. By combining experimental techniques, we were able to confirm the mechanically interlocked nature of this molecule in solution, in the gas phase and in the solid state. The behavior of the tert-butyl substituted tweezer differs greatly form that shown by the tweezer lacking of these bulky groups, whose dimeric structure is in equilibrium with the monomeric structure, therefore not showing any mechanical coercion that avoids the disassembly of the self-aggregated structure.

Shape-Adaptability and Redox-Switching Properties of a Di-Gold Metallotweezer

The use of a carbazolyl-connected di-gold(I) metallotweezer for the encapsulation of several electron-poor organic substrates, and a planar Au(III) complex containing a CNC pincer ligand, is described. The binding affinity of the receptor depends on the electron-deficient character of the planar guest, with larger association constants found for the more electron-poor guests. The X-ray diffraction molecular structures of two host:guest adducts show that the host approaches its arms in order to facilitate the optimum interaction with the surface of the planar guests, in a clear example of an guest-induced fit conformational arrangement. The electrochemical studies of the encapsulation of N,N'-dimethyl-naphthalenetetracarboxy diimide (NTCDI) show that the redox active guest is released from the receptor upon one electron reduction, thus constituting an example of redox-switchable binding.

Single-Photon Near-Infrared-Responsiveness from the Molecular to the Supramolecular Level via Platination of Pentacenes

Near-infrared (NIR) responsiveness is important for various applications. Currently, single-photon NIR-responsive systems are rare compared to systems that display two-photon absorption and triplet-triplet annihilation processes. Supramolecular stacking of photo-responsive chromophores results in decreased efficiency due to space-confinement effects. Herein we show that σ-platination of pentacenes is a feasible protocol to build single-photon NIR-responsive systems, with advantages including a low HOMO-LUMO energy gap, high photochemical efficiency, and pathway specificity. The pentacene-to-endoperoxidation transformation is accompanied by color and absorbance changes. The high photo-oxygenation efficiency of σ-platinated pentacenes facilitates NIR responsiveness in one-dimensional supramolecular polymers, resulting in the disappearance of supramolecular chirality signals and disruption of self-assembled nanofibers. Overall, the σ-platination strategy opens up new avenues toward NIR photo-responsive materials at the molecular and supramolecular levels.

Binding of a TlCl Entity by a Tetragold Tetramercaptothiacalixarene Metalloligand via Metallophilic Interactions

The successive auration of p-tert-butyltetramercaptotetrathiacalix[4]arene, H₄ (MTC[4]), with gold(I) phosphine units was investigated. Through deprotonation with NaOMe, followed by salt metathesis reactions with (PR₃ )AuCl (R=Me, Ph) complexes with two and three [(PR₃ )Au]⁺ moieties could be prepared and isolated, namely [(Ph₃ PAu)₂ H₂ (MTC[4])] and [(Me₃ PAu)₃ H(MTC[4])]. In [(Me₃ PAu)₃ H(MTC[4])] two gold atoms already come close enough to undergo aurophilic interactions. To introduce a fourth [(PR₃ )Au]⁺ entity TlOEt had to be used for the deprotonation, which led to the finding that four gold atoms organised by the (MTC[4])^4- coordination platform are able to bind and stabilize a TlCl entity, yielding [(Me₃ PAu)₄ TlCl(MTC[4])]. As evidenced by structural and theoretical investigations the binding occurs through strong metallophilic interactions, which lead to photoluminescence at low temperatures.

Bright and Robust Phosphorescence Achieved by Non-Covalent Clipping

Phosphorescent materials with bright emission in versatile media are important for their practical applications, which require to lower the susceptibility of triplet excitons to surroundings. Herein a non-covalent clipping strategy has been developed to attain this objective, by designing a tweezer receptor to encapsulate Pt^II -based triplet emitters through two-fold π-stacking interactions. The Pt^II emitters display robust phosphorescence by virtue of synergistic rigidifying and shielding effects, which are hardly influenced by emitter concentration, oxygen content, and solvent polarity changes. The phosphorescent colors are elaborately modulated by varying ligand substitutes on Pt^II emitters. Circularly polarized phosphorescence is further amplified for chiral Pt^II emitters, by taking advantage of dual phosphorescence and chirality enhancement upon non-covalent tweezer complexation. Overall, the clipping approach paves the way for the development of high-performance phosphorescent materials with bright emission, environmental robustness, and facile color tunability.

Supramolecular Chirogenesis Induced by Platinum(II) Tweezers with Excellent Environmental Tolerance

Supramolecular chirogenesis has emerged as an effective strategy to access symmetry breaking in artificial systems. However, the chirogenic signals suffer from high susceptibility toward environmental variations. An effective strategy has been developed to address this issue by constructing platinum(II)-based tweezer/guest complexes stabilized by two-fold donor-acceptor and Pt^II -Pt^II metal-metal interactions. Upon guest encapsulation, the two pincers on the achiral Pt^II tweezer undergo a stereospecific twist to minimize steric repulsion, thus locking tweezer/guest complexes into the preferred chiral conformations. The induced chiroptical effects display outstanding solvent and temperature tolerance, ascribed to the balance between electrostatic and desolvation effects for the involved non-covalent interactions. Moreover, hierarchical and multi-component supramolecular assembly of tweezer/guest complexes provide a convenient way to modulate chirogeneic signals for their intensities.

Discrete Supramolecular Stacks Based on Multinuclear Tweezer-Type Rhodium Complexes

By taking advantage of self-complementary π-π stacking and CH-π interactions, a series of discrete quadruple stacks were constructed through the self-aggregation of U-shaped dirhodium metallotweezer complexes featuring various planar polyaromatic ligands. By altering the conjugate stacking strength and bridging ligands, assemblies with a range of topologies were obtained, including a binuclear D-shaped macrocycle, tetranuclear open-ended cagelike frameworks, and duplex metallotweezer stacking structures. Furthermore, a rare stacking interaction resulting in selective C-H activation was observed during the self-assembly process of these elaborate architectures.

Aggregation and Tunable Color Emission Behaviors of l-Glutamine-Derived Platinum(II) Bipyridine Complexes by Hydrogen-Bonding, π-π Stacking and Metal-Metal Interactions

An l-glutamine-derived functional group was introduced to the bis(arylalkynyl)platinum(II) bipyridine complexes 1-4. The emission could be switched between the ³ MLCT excited state and the triplet excimeric state through solvent or temperature changes, which is attributed to the formation and disruption of hydrogen-bonding, π-π stacking, and metal-metal interactions. Different architectures with various morphologies, such as honeycomb nanostructures and nanospheres, were formed upon solvent variations, and these changes were accompanied by ¹ H NMR and distinct emission changes. Additionally, yellow and red emissive metallogels were formed at room temperature due to the different aggregation behaviors introduced by the substituent groups on bipyridine. The thermoresponsive metallogel showed emission behavior with tunable colors by controlling the temperature. The negative Gibbs free-energy change (ΔG) and the large association constant for excimer formation have suggested that the molecules undergo aggregation through hydrogen-bonding, π-π, and metal-metal interactions, resulting in triplet excimeric emission.