Reversibly sensitizing-storing-releasing ^(1)O_(2) within a single platinum(Ⅱ)-acetylide-based metallacycle molecule via laser power modulation

Tumor hypoxia severely limits the therapeutic efficacy of photodynamic therapy(PDT) for solid tumors,which is highly dependent on tissue oxygen concentration.In this study,we developed a platinum(Ⅱ)-acetylide-based metallacycle compound bearing six 1,4-dimethylnaphthalenes(DMN) groups,and controlled the photodynamic and photothermal effects of the compound by adjusting the power of 730 nm laser to achieve reversible sensitization,storage and release of 1~O_(2) within a single molecule.The compound formed nanoparticles by self-assembly and exhibited good water solubility and biocompatibility.Under laser irradiation,the strong spin-orbit coupling of platinum atoms in the metallacycle facilitated 1~O_(2) generation.The produced 1~O_(2) was captured by the DMN carriers and transported into the hypoxic tumor,where 1~O_(2) release was triggered owing to the good photothermal effect of the extended conjugation of the metallacycle.During therapy,the metallacycle serving as a photosensitizer,1~O_(2) carrier,and photothermal reagent,achieved the synergistic therapy of PDT/PTT,demonstrating the versatility of the metallacycle.This study proposes a new strategy to develop phototherapy agents that are suitable for hypoxic tumors.

A supramolecular oligo[2]rotaxane constructed by orthogonal platinum(Ⅱ) metallacycle and pillar[5]arene-based host–guest interactions

Oligo[n]rotaxanes are one of the most extensively studied categories of mechanically bonded macromolecules.In this study,a supramolecular oligo[2]rotaxane is successfully constructed driven by platinum(Ⅱ)metallacycle and pillar[5]arene-based host–guest interactions in an orthogonal way.The supramolecular oligo[2]rotaxane is further applied in fabricating a light harvesting system.

Coordination-driven self-assembly of dibenzo-18-crown-6 functionalized Pt(Ⅱ) metallacycles

Coordination-driven self-assembly was used to construct two metallacycles of a dicarboxylatefunctionalized dibenzo-18-crown-6 in combination with either a 0° anthracene-based clip-type acceptor or a 60° phenanthrene-based acceptor. The angularities of these moieties make them suitable for the formation of a [2 + 2] rectangle and a [3 + 3] triangle, respectively. The synthesis, characterization and host-guest chemistry of two metallacycles were described and supported by31P{1H},1H NMR spectra and electrospray mass spectrometry.

Construction of a 980 nm laser-activated Pt(Ⅱ)metallacycle nanosystem for efficient and safe photo-induced bacteria sterilization

Although metal-based chemical agents have demonstrated promising bacteriostatic effects in phototherapy,their short excitation/emission wavelengths and inadequate phototherapy efficiencies make their application in vivo difficult.We therefore synthesized a novel Pt(Ⅱ)metallacycle(Pt1110)that can be activated with a 980 nm laser for photodiagnosis/treatment in deep tissue.We found that Pt1110 significantly improved photothermal conversion(95%improvement)and ^(1)O_(2) generation(ΦΔ75%increase)compared to the ligand itself 1 and was well capable of light-induced sterilization under safe laser irradiation(0.72 W/cm^(2)).In addition,Pt1110 has little to no toxicity to cells.After incorporated into liposome,Pt1110 NPs was effective in wound healing in infection and keratitis models upon laser irradiation,which was accurately observed by NIR-Ⅱfluorescence imaging.This novel metal-coordinated supramolecular material has a potential to become a universal platform for phototherapy in deep tissue.

Construction of FRET-based metallacycles with efficient photosensitization efficiency and photocatalytic activity

The fabrication of highly effective photosensitizers has received considerable attention because of their attractive functions and applications in the fields of photodynamic therapy, photosynthesis, photocatalysis, etc. Thus, it is highly desirable to develop a new approach to enhance photosensitization efficiency.Herein, through coordination-driven self-assembly, a series of metallacycles with efficient fluorescence resonance energy transfer(FRET) were effectively constructed, which displayed higher photosensitization efficiency and photocatalytic activity than their model metallacycles without FRET due to broadband absorption and singlet energy transfer from the energy acceptor to the energy donor. Moreover, iodization of fluorophores induced a significant enhancement of the photosensitization efficiency and photocatalytic activity of the metallacycles. This research provides an efficient strategy for improving photosensitization efficiency and a promising platform for the preparation of effective photosensitizers and photocatalysts.

Highly emissive perylene diimide-based bowtie-shaped metallacycles

Metallacycles hold great promise for fluorescence-based sensing due to their synthetic advantages and unique physicochemical properties. However, it remains highly challenging to develop a versatile methodology for constructing highly emissive metallacycles with targeted functionalities and therefore soughtafter properties. Herein, we report a general strategy to construct a series of highly emissive perylene diimide-based metallacycles via the self-assembly of perylene diimide-based tetrapyridyl ligand with different dicarboxylic ligands featuring fixed angles and cis-Pt(PEt_(3))_(2)(OTf)_(2). Single crystal X-ray diffraction analyses verify the formation of bowtie-like metallacycles with two triangular cavities. Notably, the fluorescence quantum yields of most assemblies exceed 98%, amongst the highest values for metallacycles.Additionally, such metallacycles exhibit sensitive fluorescence responses toward picric acid with a detection limit of 2.8 × 10^(-6)mol/L. This study not only provides a rational strategy for preparing highly emissive bowtie-shaped metallacycles, but also sheds light on their usage in the detection of picric acid and associated compounds.

Chiral Coordination Metallacycles/Metallacages for Enantioselec-tive Recognition and Separation

In recent years,chiral discrete supramolecular coordination complexes have attracted increasing interest as simple enzyme mimetics owing to their aesthetic architectures and potential applications in chiral science.This review summarizes the recent advances on chiral coordination metallacy-cles/metallacages with inherent cavities for enanti on selective recog nition and separation,including their design principles and synthesis,the in troduc-tion of chirality and functionality,structural adaptability,and host-guest bonding in enantioselective process.Finally,the perspectives on the remain-ing challenges and future opportunities are presented.

Fabrication of Neutral Supramolecular Polymeric Films via Post-electropolymerization of Discrete Metallacycles

Self-assembly post-modification has proven to be an efficient strategy to build higher-order supramolecular architectures and functional materials. In this study, we successfully realized the construction＇of a new family of neutral supramolecular polymeric films containing well-defined metallacycles as the main scaffolds through combination Of coordination-driven self-assembly with post-electropolymerization. The obtained neutral polymeric materials were fully characterized by the cyclic voltammogram （CV）, SEM, and TEM. The thickness of the films was able to be well regulated by the number of scanning cycles. Moreover, we found that the shape of the metallacycles and the number of triphenylamine moieties played important roles in the formation of the final polymer films. We believe that the introduction of the neutral metallacycles into the final polymer structures not only enriches the library of supramolecular polymeric films but also provides a new platform to study neutral molecule detection, separation, and capture.

Metallacycle Expansion and Annulation:Access to Tetrazolo-Fused Osmacycles by Reaction of Cyclic Osmium Carbyne with Sodium Azide

The reaction of a cyclic osmacarbyne complex with sodium azide led to the formation of a ring expansion-annulation product,a unique tetrazole annulated polycyclic metallacycle.The reaction proceeds by insertion of a nitrogen atom into the metal carbon triple bond and the second azide participating in the[2+3]cycloaddition.The successful isolation and characterization of metalla-azirine complex and metallapyridinium derivative strongly validated the mechanism for the formation of the title complex.The work demonstrates a new strategy to enrich the varieties of aza-metallacyclic species.

Our expedition in the construction of fluorescent supramolecular metallacycles

During the past few years, the construction of fluorescent supramolecular metallocycles has attracted extensive attention due to their diverse applications such as sensing, photoelectric devices, and mimicking complicated natural photo-processes. In this review, we will discuss how we entered the field of fluorescent supramolecular metallacycles and what we investigated in this field. The preparation of various fluorescent supramolecular metallacycles and their applications in monitoring the dynamics of coordination-driven self-assembly, sensing, catalysts, and supramolecular gels will be summarized.

Supramolecular Polymer Networks with Enhanced Mechanical Properties:The Marriage of Covalent Polymer and Metallacycle

Main observation and conclusion Supramolecular polymer networks(SPNs)have always been the focus of research due to their novel features of good processability,stimuli-responsiveness,self-healing,and recyclability.Herein,we report the preparation of a metallacycle-linked supramolecular gel via orthogonal metal-ligand interactions and host-guest interactions.A triangular metallacycle with three appended 21-crown-7(21C7)units was obtained by the metal coordination of nickel(II)-salen-based dipyridyl ligands and platinum(II)acceptors.The integration of this metallacycle and traditional copolymer bearing secondary ammonium salts constructed a SPN via host-guest recognition between 21C7 units and ammonium salts,and a supramolecular gel further formed at high concentration.Multiple stimulus responsiveness and self-healing properties of gel were observed.The gel exhibited better stretchability compared to relative gel formed by copolymer alone owing to the synergistic effect of covalent bonds and supramolecular interactions.Moreover,compared to the model gel without metallacycles,the gel showed higher storage and loss moduli,and exhibited stronger stiffness in the self-healing tests performed with rheometer,indicating the metallacycle played an important role in improving the stiffness and self-healing of the gel.Therefore,the feasible approach to the formation of SPNs by the marriage of covalent polymers and metallacycles is expected to open a new way to design novel SPNs.

Conformational effect on fluorescence emission of tetraphenylethylene-based metallacycles

Herein,we designed and constructed two metallacycles,1 and 2,to illustrate the conformational effect of isomeric AIE fluoropho res on the platfo rm of supramolecular coordination complexe s(SCCs).Specifically,the dangling phenyl rings in TPE units of the metallacycle 1 align completely outside the main cyclic structure,while in the metallacycle 2,these phenyl rings align half inside and half outside.The experimental results showed that two metallacycles exhibited different behaviors in terms of AIE fluorescence and chemical sensing,which could be attributed to the subtle structural difference of the TPE units.This work repre sents the unification of topics such as self-assembly,AIE,and chemical sensing,and further promotes the understanding for the structure-property relationship of isomeric AIE fluorophores.

A Near-Infrared Organoplatinum(Ⅱ) Metallacycle Conjugated with Heptamethine Cyanine for Trimodal Cancer Therapy

Discrete Pt(Ⅱ)metallacycles have attracted particular attention for the chemotherapeutic treatment of cancer.However,a single chemotherapy cannot simultaneously balance efficiency and safety because the continuous administration throughout the entire therapy period will lead to inefficient therapy and potentially long-term systemic toxicity.Therefore,the development of a novel organoplatinum(Ⅱ)metallacycle with multimodal treatment capabilities is urgently needed to overcome these issues.Herein,a discrete Pt(II)metallacycle(SCY)bearing the near-infrared(NIR)photosensitizer heptamethine cyanine was fabricated and further encapsulated by amphiphilic 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-methoxy(polyethyleneglycol)(DSPEmPEG)to form P@SCY nanoparticles.Heptamethine cyanine,which has excellent photoconversion efficiency,can generate reactive oxygen species(ROS)and heat simultaneously,and the cyanine moiety can target mitochondria in cancer cells due to their quaternary ammonium salt cations,which improve the effect of phototherapy.Due to its excellent phototherapy and chemotherapy properties,P@SCY exhibited remarkable trimodal therapeutic effects[chemo-/photodynamic therapy(PDT)/photothermal therapy(PTT)]against cancer cells(HepG2 cells,MCF-7 cells,and 4T1 cells)in vitro.Furthermore,in vivo results also confirmed thatP@SCY had superior antitumor properties with minimal side effects in the 4T1 tumor model.Thiswork presents a practicable approach to develop a multifunctional organoplatinum(Ⅱ)metallacycle for multimodal tumor therapy.

Cyanostilbene-based near-infrared emissive platinum(Ⅱ) metallacycles for cancer theranostics

In this work,a near-infrared emissive dipyridyl ligand was synthesized and used to prepare three platinum(II)metallacycles with different shapes via metal-coordination-driven self-assembly with different platinum(II)precursors.These metallacycles were further used for both cell imaging and cancer therapy,offering a new type of theranostic agents towards cancer treatment.

Photoacoustic imaging-guided chemo-photothermal combinational therapy based on emissive Pt(Ⅱ)metallacycle-loaded biomimic melanin dots

Pt(Ⅱ)-based metallacycles,as an important family of supramolecular coordination complexes(SCCs),have exhibited excellent antitumor activity at the cell level.However,the biomedical applications of Pt(Ⅱ)-based metallacycles for animal studies are still hindered by their poor stability,non-targeted tumour,and lack of detectable feedback for evaluating therapeutic progress.Herein,we propose a strategy that introduces melanin dots as a biomedical platform to load bright-emission Pt(Ⅱ)-based metallacycles,thereby constructing a theranostic agent that enables photoacoustic imaging(PAI)-guided chemo-photothermal combinational therapy.Melanin dots act as a protective carrier to preserve the integrity of Pt(Ⅱ)-based metallacycles before uptake by tumour tissues.Meanwhile,the PAI signal from melanin dots furnishes more comprehensive information on the tumour.Moreover,the heat generated after NIR laser irradiation can not only trigger the apoptosis of tumour cells but also promote the deeper penetration of Pt(Ⅱ)-based SCCs into tumour tissue,thus enhancing the efficiency of chemotherapy.

Hierarchical assembly of uranyl metallacycles involving macrocyclic hosts

Actinide metallacycles are an emerging class of functional coordination assemblies,but multi-level assembly from metallacycle units toward hierarchical supramolecular structures are still rarely investigated.In this work,we put forward a novel supramolecular inclusion-based method through introducing two macrocyclic hosts,cucurbit[7]uril(CB[7])and cucurbit[8]uril(CB[8])to facilitate hierarchical assembly of uranyl metallacycles with higher complexity,and successfully prepare two different kinds of uranyl metallacycle-based complexes with intriguing hierarchical structures,a CB[7]-based four-member molecular necklace([4]MN)and a CB[8]-involved ring-in-ring supramolecular polymer chain.The results obtained here prove the feasibility of supramolecular inclusion for regulating coordination assembly of uranyl metallacycles and related hierarchical structures.It is believed that this method can be used to achieve the construction of actinide coordination assemblies with higher structural complexity.

SYNTHESIS OF TETRAPHENYLBUTADIENE LANTHANIDE METALLACYCLES

The cyclic derivatives of transition metals have been extensively investigated in recent years since they are believed to serve as key intermediates in various homogeneous catalytic processes of olefine and alkyne metathesis. The synthesis of the title compounds has not been reported before.

Fluorescence-resonance energy transfer(FRET)within the fluorescent metallacycles

During past few years,the construction of fluorescent metallacycles featuring the fluorescenceresonance energy transfer behavior has attracted extensive attention due to their diverse applications such as real-time monitoring the dynamics of coordination-driven self-assembly,photoswitching fluorescence-resonance energy transfer,and light-controlled generation of singlet oxygen for cancer therapy.This review focuses on the recent advances on the design principles,preparation methods,optical properties,and the wide applications of fluorescent metallacycles with the FRET property.

Synthesis of a Novel Discrete Metallacycle Complex Self-assembled into a 3D Hydrogen-binding Supramolecular Structure

A novel discrete dinuclear metaUacyclic copper（Ⅱ） complex, [Cu2L2（H2O）2]·3H2O （1） has been firstly prepared where L is derived from the 1 ; 2 condensation of 2,2＇-bipyridyl-3,3＇-diformylhydrazide and acetone during the formation of the complex. Single-crystal X-ray diffraction analysis determines that the complex consists of dinuclear metallacyclic units [Cu2L2（H2O）2] where two metal centers are linked together through two bis（chelating） bridge ligands L to form a bizarre cavity with size 0.9417 nm× 0.4999 nm× 0.6930 nm. Interestingly, the metal coordination also creates hydrogen bond sites that further aggregate these metallacycles into a 3D supramolecular structure with 2D perpendicular hydrophilic tunnels in crystal.

Heavier Group 14 Congeners of Metalla-isobenzenes:Access to Metalla-isosilabenzene and Metalla-isogermabenzene by One-Pot Reactions

Metalla-isosilabenzenes and metalla-isogermabenzenes have been successfully synthesized by the formal[5+1]-cycloaddition of diethynylsilane or diethynylgermane with simple metal complexes.This is the first example of a heavier Group 14 metalla-isobenzene isomer bearing a cumulative double bond motif within a metallacycle.These novel complexes were fully characterized by NMR spectroscopy and single-crystal X-ray diffraction analysis.The stabilization of the cyclic metal-vinylidene complexes has been analyzed using density functional theory(DFT)calculations.When the metalla-isosilabenzenes bearing Si—H bond were treated with the trityl salt as a hydride scavenger,the formation of silylium cation was observed spectroscopically.Both of metalla-isosilabenzenes and metalla-isogermabenzenes can readily undergo migratory insertion reactions to furnish siloles or germoles.