Achieving Circularly Polarized Phosphorescence through Noncovalent Clipping of Metallotweezers.

Circularly polarized phosphorescent materials, based on host-guest complexation, have received significant attention due to their outstanding emission performance in solutions. Recent studies have primarily focused on macrocyclic host-guest complexes. To broaden the scope of this research, there is a keen pursuit of developing novel chiral phosphorescent host-guest systems. Metallotweezers with square-planar d8 transition metal complexes emerge as promising candidates for achieving this objective. Specifically, metallotweezers, comprising platinum(II) terpyridine and gold(III) diphenylpyridine pincers on a diphenylpyridine scaffold, have been designed and synthesized. Due to the preorganization effect rendered by the diphenylpyridine scaffold, the resulting metallotweezers are capable of complexing with each other and forming quadruple stacking structures. The phosphorescent emission is enhanced owing to the synergistic rigidifying and shielding effects. Meanwhile, the steric effect of chiral (1R) pinene units on the platinum(II) terpyridine pincers results in a stereospecific twist for the quadruple stacking structures. Thus, the chirality transfers from the molecular to the supramolecular level. By a combination of phosphorescent enhancement and supramolecular chirality for the clipping complex, circularly polarized phosphorescent emission is achieved. Overall, noncovalent clipping of metallotweezers exemplified in the current study presents a novel and effective approach toward solution-processable circularly polarized phosphorescent materials.

Enhanced Near-infrared Phosphorescent Emission Modulated by Clipping of Metallotweezers in Aqueous Media.

Near-infrared phosphorescent materials have received significant attention due to their potential applications in bioimaging and diagnostics. Although, many types of organic phosphors with near-infrared emission have been developed, the low phosphorescence efficiency in aqueous solution hampers their practical applications in biological systems. Hence, there is an urgent need to develop near-infrared phosphorescent materials with high emission efficiency in aqueous media. Metallotweezers, based on d8 transition metal complexes, emerge as the potential candidates for realizing this objective. Specifically, metallotweezers, featuring two positively charged platinum(II) terpyridine and neutral gold(III) diphenylpyridine pincers on diphenylpyridine spacer, have been designed and synthesized, respectively. The pre-organization effect, rendered by the rigid spacer, enables the resulting metallotweezers to complex with each other, resulting in the formation of clipping complex. The synergistic rigidifying and shielding effects of clipping structure results in enhanced phosphorescent emission intensity. Concurrently, due to phase segregation between the clipping units and the polyethylene glycol tail, the clipping complex undergoes self-assembly in aqueous solution, resulting in phosphorescent emission in the near-infrared region. Overall, non-covalent clipping of metallotweezers illustrated in this study presents a new and effective approach toward near-infrared phosphorescent materials.

Dual supramolecular chirogenesis based on platinum(II) metallotweezers.

Optically active platinum(II) metallotweezers demonstrate both self-complexation and host-guest complexation capabilities, leading to two distinct supramolecular chirogenic signals in the visible region.

[2.2]Paracyclophane-bridged platinum(II) complexes for silver(I) recognition with emission enhancement.

A [2.2]paracyclophane-bridged bimetallic alkynylplatinum(II) terpyridyl complex displays severe emission quenching due to the presence of intramolecular π-π interactions. It undergoes an adaptive conformational change upon recognizing Ag+, which attenuates the intramolecular stacking strength and thereby exhibits "turn-on" emission character.

Controlled Formation of a Main Chain Supramolecular Polymer Based on Metal-Ligand Interactions and a Thiol-Ene Click Reaction.

Supramolecular polymers with multiple functionalities and hierarchical structures have received considerable attention and become a hot research topic over the past years. Herein, a main-chain supramolecular polymer has been successfully fabricated by using metal-ligand interactions and a thiol-ene click reaction. 1 H NMR, UV/Vis, DOSY, and viscosity measurements were carried out to investigate the molecular recognition and the process of supramolecular polymerization. From the study, the orthogonality between thiol-ene click reactions and the terpyridine-metal ions complexation behavior was testified, and supramolecular polymeric assemblies could be constructed by a one pot method. In the meantime, due to the incorporation of metal-ligand interactions, the supramolecular polymer shows stimuli-responsive properties toward chemical stimuli. Hence, this work could provide a methodology for developing supramolecular polymers as smart materials.

Donor-acceptor-type supramolecular polymers on the basis of preorganized molecular tweezers/guest complexation.

The bottom-up self-assembly of donor-acceptor (D-A) units has received tremendous attention in recent years. Charge-transfer interactions, which are inherently embedded in D-A pairs, have suffered from some disadvantages such as erratic arrangements and weak binding affinity, thus hampering the precise arrangement of D-A units into long-range-ordered supramolecular polymers. To address this issue, a feasible protocol is to incorporate D-A units into molecular tweezers/guest recognition motifs, which concurrently feature high complexation directionality, strong binding affinity and stimuli-responsiveness. In this tutorial review, we have summarized the recent advances on the tweezering directed formation of D-A-type supramolecular polymers, with particular emphasis on the design principles of monomers and macroscopic behaviors of supramolecular polymers, together with future challenges in this research field.

Metallo-supramolecular polymers derived from benzothiadiazole-based platinum acetylide complexes for fluorescent security application.

Metallo-supramolecular polymers with the incorporation of benzothiadiazole-substituted organoplatinum moiety have been successfully constructed. The designed monomer displays intense fluorescence signals, which are severely quenched upon the supramolecular polymerization process. On-off switching of fluorescence can be further exploited for data security materials in response to the chemical stimuli. Accordingly, the resulting supramolecular polymers can be regarded as a novel and efficient candidate toward information processing applications.

Mechanically Linked Poly[2]rotaxanes Constructed via the Hierarchical Self-Assembly Strategy.

Mechanically linked poly[2]rotaxanes have been successfully constructed via the hierarchical self-assembly strategy. The integration of two noninterfering noncovalent recognition motifs facilitates chain extension of the B21C7-based [2]rotaxane monomer, demonstrating the capabilities to form self-standing films with preferable transparency and softness.

Construction of supramolecular hyperbranched polymers via the "tweezering directed self-assembly" strategy.

A bis-alkynylplatinum(II) terpyridine tweezer-alkynylgold(III) diphenylpyridine guest is shown to maintain the specific complexation in the presence of a B21C7-secondary ammonium salt recognition motif, which facilitates the formation of supramolecular hyperbranched polymers via the "tweezering directed self-assembly" strategy.

Cooperative complexation of amino acid derivatives to platinum acetylide-based bolaamphiphile.

A platinum(II) acetylide-based bolaamphiphile equipped with two peripheral B18C6 moieties has been successfully prepared, which demonstrates cooperative recognition behavior toward l-alanine ester salt in chloroform. In a polar methanol/chloroform (3/1, v/v) medium, the amino acid additives influence the aggregation of the bolaamphiphile significantly, leading to the morphological transition from nanospherical to disordered structures. The adaptive properties of the current host-guest binary system will benefit the development of stimuli-responsive supramolecular materials.

Responsive supramolecular polymers based on the bis[alkynylplatinum(II)] terpyridine molecular tweezer/arene recognition motif.

Supramolecular polymers are constructed based on the novel bis[alkynylplatinum(II)] terpyridine molecular tweezer/pyrene recognition motif. Successive addition of anthracene as the diene and cyano-functionalized dienophile triggers the reversible supramolecular polymerization process, thus advancing the concept of utilizing Diels-Alder chemistry to access stimuli-responsive materials in compartmentalized systems.

Main-chain supramolecular polymers based on orthogonal benzo-21-crown-7/secondary ammonium salt and terpyridine/metal ion recognition motifs.

Orthogonal self-assembly of multiple components represents an efficient strategy to afford hierarchical and multifunctional assemblies. Here, we demonstrate the orthogonal recognition behaviors between benzo-21-crown-7/secondary ammonium salt and terpyridine/metal ions (Fe(2+) or Zn(2+) ) recognition motifs. Main-chain supramolecular polymers are subsequently achieved via "one-pot" mixing of the three monomers together (heteroditopic monomer 1, homoditopic secondary ammonium salt monomer 2, and Fe(BF4 )2 •6H2 O or Zn(OTf)2 ), which are confirmed by (1) H NMR, UV-Vis, DOSY, and viscosity measurements. Moreover, different metal ions (Fe(2+) or Zn(2+) ) exert considerable effects on the size of the resulting supramolecular polymers. Integration of two different types of non-covalent interactions renders dynamic and responsive properties for the resulting supramolecular polymers, as triggered by a variety of external stimuli such as temperature, potassium cation, as well as stronger chelating ligands. Therefore, the current work is a prerequisite for the future application of such orthogonal assemblies as intelligent supramolecular materials.

Formation of stimuli-responsive supramolecular polymeric assemblies via orthogonal metal-ligand and host-guest interactions.

Linear supramolecular polymers, assembled via the combination of orthogonal terpyridine-Zn(2+) and benzo-21-crown-7/secondary ammonium salt recognition motifs, exhibit dynamic properties responsive to various external stimuli.