Light-Responsive Supramolecular Liquid-Crystalline Metallacycle for Orthogonal Multimode Photopatterning.

The development of multimode photopatterning systems based on supramolecular coordination complexes (SCCs) is considerably attractive in supramolecular chemistry and materials science, because SCCs can serve as promising platforms for the incorporation of multiple functional building blocks. Herein, we report a light-responsive liquid-crystalline metallacycle that is constructed by coordination-driven self-assembly. By exploiting its fascinating liquid crystal features, bright emission properties, and facile photocyclization capability, a unique system with spatially-controlled fluorescence-resonance energy transfer (FRET) is built through the introduction of a photochromic spiropyran derivative, which led to the realization of the first example of a liquid-crystalline metallacycle for orthogonal photopatterning in three-modes, namely holography, fluorescence, and photochromism.

Construction of an Artificial Light-Harvesting System with Efficient Photocatalytic Activity in an Aqueous Solution Based on a FRET-Featuring Metallacage.

Over the past few decades, the design and construction of high-efficiency artificial light-harvesting systems (LHSs) involving multistep fluorescence-resonance energy transfer (FRET) processes have gradually received considerable attention within wide fields ranging from supramolecular chemistry to chemical biology and even materials science. Herein, through coordination-driven self-assembly, a novel tetragonal prismatic metallacage featuring a FRET process using tetraphenylethene (TPE) units as donors and BODIPY units as acceptors has been conveniently synthesized. Subsequently, taking advantage of supramolecular hydrophobic interactions, a promising artificial LHS involving two-step FRET processes from TPE to BODIPY and then to Nile Red (NiR) has been successfully fabricated in an aqueous solution using the FRET-featuring metallacage, NiR, and an amphiphilic polymer (mPEG-DSPE). Notably, this obtained aqueous LHS exhibits highly efficient photocatalytic activity in the dehalogenation of a bromoacetophenone derivate. This study provides a unique strategy for fabricating artificial LHSs in aqueous solutions with multistep FRET processes and further promotes the future development of mimicking the photosynthesis process.

Construction of Covalent Organic Cages with Aggregation-Induced Emission Characteristics from Metallacages for Mimicking Light-Harvesting Antenna.

A series of covalent organic cages built from fluorophores capable of aggregation-induced emission (AIE) were elegantly prepared through the reduction of preorganized M2 (LA )3 (LB )2 -type metallacages, simultaneously taking advantage of the synthetic accessibility and well-defined shapes and sizes of metallacages, the good chemical stability of the covalent cages as well as the bright emission of AIE fluorophores. Moreover, the covalent cages could be further post-synthetically modified into an amide-functionalized cage with a higher quantum yield. Furthermore, these presented covalent cages proved to be good energy donors and were used to construct light-harvesting systems employing Nile Red as an energy acceptor. These light-harvesting systems displayed efficient energy transfer and relatively high antenna effect, which enabled their use as efficient photocatalysts for a dehalogenation reaction. This research provides a new avenue for the development of luminescent covalent cages for light-harvesting and photocatalysis.

Orthogonal Self-Assembly of a Two-Step Fluorescence-Resonance Energy Transfer System with Improved Photosensitization Efficiency and Photooxidation Activity.

During the past few decades, fabrication of multistep fluorescence-resonance energy transfer (FRET) systems has become one of the most attractive topics within supramolecular chemistry, chemical biology, and materials science. However, it is challenging to efficiently prepare multistep FRET systems with precise control of the distances between locations and the numbers of fluorophores. Herein we present the successful fabrication of a two-step FRET system bearing specific numbers of anthracene, coumarin, and BODIPY moieties at precise distances and locations through an efficient and controllable orthogonal self-assembly approach based on metal-ligand coordination and host-guest interactions. Notably, the photosensitization efficiency and photooxidation activity of the two-step FRET system gradually increased with the number of energy transfer steps. For example, the two-step FRET system exhibited 1.5-fold higher 1O2 generation efficiency and 1.2-fold higher photooxidation activity than that of its corresponding one-step FRET system. This research not only provides the first successful example of the efficient preparation of multistep FRET systems through orthogonal self-assembly involving coordination and host-guest interactions but also pushes multistep FRET systems toward the application of photosensitized oxidation of a sulfur mustard simulant.

Visible-Light-Driven Rotation of Molecular Motors in Discrete Supramolecular Metallacycles.

The organization of molecular motors in supramolecular assemblies to allow the amplification and transmission of motion and collective action is an important step toward future responsive systems. Metal-coordination-driven directional self-assembly into supramolecular metallacycles provides a powerful strategy to position several motor units in larger structures with well-defined geometries. Herein, we present a pyridyl-modified molecular motor ligand (MPY) which upon coordination with geometrically distinct di-Pt(II) acceptors assembles into discrete metallacycles of different sizes and shapes. This coordination leads to a red-shift of the absorption bands of molecular motors, making these motorized metallacycles responsive to visible light. Photochemical and thermal isomerization experiments demonstrated that the light-driven rotation of the motors in the metallacycles is similar to that in free MPY in solution. CD studies show that the helicity inversions associated with each isomerization step in the rotary cycle are preserved. To explore collective motion, the trimeric motor-containing metallacycle was aggregated with heparin through multiple electrostatic interactions, to construct a multi-component hierarchical system. SEM, TEM, and DLS measurements revealed that the photo- and thermal-responsive molecular motor units enabled selective manipulation of the secondary supramolecular aggregation process without dissociating the primary metallacycle structures. These visible-light-responsive metallacycles, with intrinsic multiple rotary motors, offer prospects for cooperative operations, dynamic hierarchical self-assembled systems, and adaptive materials.

Acid-Activated Motion Switching of DB24C8 between Two Discrete Platinum(II) Metallacycles.

The precise operation of molecular motion for constructing complicated mechanically interlocked molecules has received considerable attention and is still an energetic field of supramolecular chemistry. Herein, we reported the construction of two tris[2]pseudorotaxanes metallacycles with acid-base controllable molecular motion through self-sorting strategy and host-guest interaction. Firstly, two hexagonal Pt(II) metallacycles M1 and M2 decorated with different host-guest recognition sites have been constructed via coordination-driven self-assembly strategy. The binding of metallacycles M1 and M2 with dibenzo-24-crown-8 (DB24C8) to form tris[2]pseudorotaxanes complexes TPRM1 and TPRM2 have been investigated. Furthermore, by taking advantage of the strong binding affinity between the protonated metallacycle M2 and DB24C8, the addition of trifluoroacetic acid (TFA) as a stimulus successfully induces an acid-activated motion switching of DB24C8 between the discrete metallacycles M1 and M2. This research not only affords a highly efficient way to construct stimuli-responsive smart supramolecular systems but also offers prospects for precisely control multicomponent cooperative motion.

Artificial Light-Harvesting Systems Based on AIEgen-branched Rotaxane Dendrimers for Efficient Photocatalysis.

Aiming at the construction of novel platform for efficient light harvesting, the precise synthesis of a new family of AIEgen-branched rotaxane dendrimers was successful realized from an AIEgen-functionalized [2]rotaxane through a controllable divergent approach. In the resultant AIE macromolecules, up to twenty-one AIEgens located at the tails of each branches, thus making them the first successful example of AIEgen-branched dendrimers. Attributed to the solvent-induced switching feature of the rotaxane branches, the integrated rotaxane dendrimers displayed interesting dynamic feature upon the aggregation-induced emission (AIE) process. Moreover, novel artificial light-harvesting systems were further constructed based on these AIEgen-branched rotaxane dendrimers, which revealed impressive generation-dependent photocatalytic performances for both photooxidation reaction and aerobic cross-dehydrogenative coupling (CDC) reaction.

Construction of Supramolecular Liquid-Crystalline Metallacycles for Holographic Storage of Colored Images.

Design and construction of new functionalized supramolecular coordination complexes (SCCs) via coordination-driven self-assembly strategy is highly important in supramolecular chemistry and materials science. Herein, we present a family of well-defined metallacycles decorated with mesogenic forklike dendrons through the strategy of coordination-driven self-assembly. Due to the existence of mesogenic forklike dendrons, the obtained metallacycles displayed the smectic A liquid crystal phase at room temperature while their precursors exhibited the rectangular columnar liquid crystal phase. Interestingly, by taking advantage of the electrostatic interactions between the positively charged metallacycle and the negatively charged heparin, the doping of heparin induced a significant change of the liquid-crystalline behaviors of metallacycles. More importantly, the prepared liquid-crystalline metallacycles could be further applied for holographic storage of colored images. Notably, the rhomboidal metallacycle and hexagonal metallacycle gave rise to different holographic performances although they featured a similar liquid crystal phase behavior. Therefore, this research not only provides the first successful example of supramolecular liquid-crystalline metallacycles for holographic storage of colored images but also opens a new door for supramolecular liquid-crystalline metallacycles toward advanced optical applications.

Radical-Induced Hierarchical Self-Assembly Involving Supramolecular Coordination Complexes in Both Solution and Solid States.

To explore a new supramolecular interaction as the main driving force to induce hierarchical self-assembly (HSA) is of great importance in supramolecular chemistry. Herein, we present a radical-induced HSA process through the construction of well-defined rhomboidal metallacycles containing triphenylamine (TPA) moieties. The light-induced radical generation of the TPA-based metallacycle has been demonstrated, which was found to subsequently drive hierarchical self-assembly of metallacycles in both solution and solid states. The morphologies of nanovesicle structures and nanospheres resulting from hierarchical self-assembly have been well-illustrated by using TEM and high-angle annular dark-field STEM (HAADF-STEM) micrographs. The mechanism of HSA is supposed to be associated with the TPA radical interaction and metallacycle stacking interaction, which has been supported by the coarse-grained molecular dynamics simulations. This study provides important information to understand the fundamental TPA radical interaction, which thus injects new energy into the hierarchical self-assembly of supramolecular coordination complexes (SCCs). More interestingly, the stability of TPA radical cations was significantly increased in these metallacycles during the hierarchical self-assembly process, thereby opening a new way to develop stable organic radical cations in the future.

Supramolecular Polymer Cross-Linked by Discrete Tris-[2]pseudorotaxane Metallacycles and Its Redox-Responsive Behavior.

A new discrete hexagonal metallacycle M containing tris-[2]pseudorotaxane moiety has been successfully designed and synthesized via coordination-driven self-assembly. The newly designed tris-[2]pseudorotaxane metallacycle was well characterized with nuclear magnetic resonance and mass spectra analysis. Such tris-[2]pseudorotaxane metallacycle M and pillar[5]arene dimer (PD) could further form a new family of cross-linked redox-responsive supramolecular polymer M⊃(PD)3 through a host-guest interaction. Interestingly, the polymer M⊃(PD)3 displayed redox-responsive behavior and showed tuned weight-average diffusion coefficients D upon redox stimuli, which is attributed to the changed coordination geometries of [Cu(phen)2]+ and [Cu(phen)2]2+ in such system.

Hierarchical self-assembly of discrete bis-[2]pseudorotaxane metallacycle with bis-pillar[5]arene via host-guest interactions and their redox-responsive behaviors.

A discrete rhomboidal metallacycle R functionalized with bis-[2]pseudorotaxane of [Cu(phenanthroline)2]+ derivatives was successfully synthesized via coordination-driven self-assembly. Furthermore, the host-guest complexation of such a bis-[2]pseudorotaxane metallacycle with a bis-pillar[5]arene (bisP5) allowed for the formation of a new family of cross-linked supramolecular polymers R⊃(bisP5)2, which displayed interesting redox-responsive properties. By taking advantage of the substantial structural differences between the coordination geometries of [Cu(phenanthroline)2]+ and [Cu(phenanthroline)2]2+, the weight-average diffusion coefficients D of the supramolecular polymer were adjusted through changing the redox state of the Cu(i)/Cu(ii) complexes.

Efficient self-assembly of heterometallic triangular necklace with strong antibacterial activity.

Sophisticated mechanically interlocked molecules (MIMs) with interesting structures, properties and applications have attracted great interest in the field of supramolecular chemistry. We herein report a highly efficient self-assembly of heterometallic triangular necklace 1 containing Cu and Pt metals with strong antibacterial activity. Single-crystal X-ray analysis shows that the finely arranged triangular necklace 1 has two racemic enantiomers in its solid state with intriguing packing motif. The superior antibacterial activity of necklace 1 against both standard and clinically drug-resistant pathogens implies that the presence of Cu(I) center and platinum(II) significantly enhance the bacterium-binding/damaging activity, which is mainly attributed to the highly positively charged nature, the possible synergistic effect of heterometals in the necklace, and the improved stability in culture media. This work clearly discloses the structure-property relationships that the existence of two different metal centers not only facilitates successful construction of heterometallic triangular necklace but also endows it with superior nuclease properties and antibacterial activities.

Photoswitchable Förster resonance energy transfer (FRET) within a heterometallic Ir-Pt macrocycle.

A new heterometallic macrocycle with photochromic properties was succesfully constructed through coordination-driven self-assembly, which features interesting photoswitchable Förster resonance energy transfer (FRET) behaviour.