Emissive Platinum(II) Cages with Reverse Fluorescence Resonance Energy Transfer for Multiple Sensing

Highly Efficient Self-Assembly of Heterometallic [2]Catenanes and Cyclic Bis[2]catenanes via Orthogonal Metal-Coordination Interactions

Although catenated cages have been widely constructed due to their unique and elegant topological structures, cyclic catenanes formed by the connection of multiple catenane units have been rarely reported. Herein, based on the orthogonal metal-coordination-driven self-assembly, we prepare a series of heterometallic [2]catenanes and cyclic bis[2]catenanes, whose structures are clearly evidenced by single-crystal X-ray analysis. Owing to the multiple positively charged nature, as well as the potential synergistic effect of the Cu(I) and Pt(II) metal ions, the cyclic bis[2]catenanes display broad-spectrum antibacterial activity. This work not only provides an efficient strategy for the construction of heterometallic [2]catenanes and cyclic bis[2]catenanes but also explores their applications as superior antibacterial agents, which will promote the construction of advanced supramolecular structures for biomedical applications.

Enantiopure trigonal bipyramidal coordination cages templated by in situ self-organized D2h-symmetric anions

The control of a molecule's geometry, chirality, and physical properties has long been a challenging pursuit. Our study introduces a dependable method for assembling D3-symmetric trigonal bipyramidal coordination cages. Specifically, D2h-symmetric anions, like oxalate and chloranilic anions, self-organize around a metal ion to form chiral-at-metal anionic complexes, which template the formation of D3-symmetric trigonal bipyramidal coordination cages. The chirality of the trigonal bipyramid is determined by the point chirality of chiral amines used in forming the ligands. Additionally, these cages exhibit chiral selectivity for the included chiral-at-metal anionic template. Our method is broadly applicable to various ligand systems, enabling the construction of larger cages when larger D2h-symmetric anions, like chloranilic anions, are employed. Furthermore, we successfully produce enantiopure trigonal bipyramidal cages with anthracene-containing backbones using this approach, which would be otherwise infeasible. These cages exhibit circularly polarized luminescence, which is modulable through the reversible photo-oxygenation of the anthracenes.

Enhancing the Photosensitivity of Hypocrellin A by Perylene Diimide Metallacage-Based Host-Guest Complexation for Photodynamic Therapy

The development of supramolecular hosts which can efficiently encapsulate photosensitizers to improve the photodynamic efficacy holds great promise for cancer therapy. Here, we report two perylene diimide-based metallacages that can form stable host-guest complexes with planar conjugated molecules including polycyclic aromatic hydrocarbons and photosensitizers (hypocrellin A). Such host-guest complexation not only prevents the aggregation of photosensitizers in aqueous environments, but also offers fluorescence resonance energy transfer (FRET) from the metallacage to the photosensitizers to further improve the singlet oxygen generation (ΦΔ = 0.66). The complexes are further assembled with amphiphilic polymers, forming nanoparticles with improved stability for anticancer study. Both in vitro and in vivo studies indicate that the nanoparticles display excellent anticancer activities upon light irradiation, showing great potential for cancer photodynamic therapy. This study provides a straightforward and effective approach for enhancing the photosensitivity of conventional photosensitizers via host-guest complexation-based FRET, which will open a new avenue for host-guest chemistry-based supramolecular theranostics.

Precise Regulation the Multiemission Based on Soft Double Salt for Information Encryption

Manipulation of multiemissive luminophores is meaningful for exploring luminescent materials. Herein, we report a soft double salt assembly strategy that could result in well-organized nanostructures and different luminescence based on multiple weak intermolecular interactions thanks to the existence of electrostatic attraction between the anionic and cationic platinum(II) complexes. The cationic complexes B1 and B2 can coassemble with anionic complex A, respectively, and the emission switches from monomeric and excimeric emission to the triplet metal-metal-to-ligand charge transfer (3MMLCT) along with morphology changes from 0-dimensional (0-D) nanospheres to 3-dimensional (3-D) nanostructures. It is demonstrated that an isodesmic growth mechanism is adopted during the spontaneous self-assembly process, and the relative negative ΔG values make the anionic and cationic complex molecules prefer to form aggregates based on π-π stacking, Pt···Pt interactions, and electrostatic interactions. The coassembly strategy between anionic and cationic complexes endows them with multicolor luminescent and apparent color as optical materials for advanced information encryption.

Development of highly sensitive dual-enhanced fluorescence quenching immunochromatographic test strips based on Pt nanoprobes

The fluorescence-quenching method is crucial in vitro analysis, particularly for immunochromatographic test strips (ICTs) using noble metal nanoparticles as probes. However, ICTs still fall short in meeting the requirements for the detection of traces biomarkers due to the noble metal nanoparticles can only quench fluorescence of the dyes within a confined distance. Interestingly, noble metal nanoparticles, such as Pt NPs cannot only perform fluorescence-quenching ability based on the Förster resonance energy transfer (FRET), but also show perfect oxidase-like catalytic performance on many kinds of substrates, such as 3,3',5,5' -tetramethylbenzidine (TMB). We observed that the oxTMB (the oxidation products of TMB) exhibited notable effectiveness in quenching Cy5 fluorescence by the strong inner filter effect (IFE), which obviously improved the fluorescence-quenching efficiency with extremely low background signal. Through the dual-enhanced fluorescence quenching mechanism, the fluorescence quenching constant (Kn) was 661.24-fold that of only Pt NPs on the NC membrane. To validate the feasibility of this technique, we employed two types of biomarkers, namely microRNA (miR-15a-5p) and the signature protein (PSA). The sensitivity of miR-15a-5p was 9.286 × 10-18 mol/L and 17.5-fold more than that based on Pt NPs. As for the PSA, the LOD (0.6265 pg/mL) was 15.5-fold enhancement more sensitive after catalysis. Overall, the dual-enhanced fluorescence quenching rFICTs could act as a practical detection for biomarker in real samples.

Precise Post-Synthetic Modification of Heterometal-Organic Capsules for Selectively Encapsulating Tetrahedral Anions

Post-synthetic modification plays a crucial role in precisely adjusting the structure and functions of advanced materials. Herein, we report the self-assembly of a tubular heterometallic Pd3Cu6L16 capsule that incorporates Pd(II) and CuL1 metalloligands. This capsule undergoes further modification with two tridentate anionic ligands (L2) to afford a bicapped Pd3Cu6L16L22 capsule with an Edshammer polyhedral structure. By employing transition metal ions, acid, and oxidation agents, the bicapped capsule can be converted into an uncapped one. This uncapped form can then revert back to the bicapped structure on the addition of Br- ions and a base. Interestingly, introducing Ag+ ions leads to the removal of one L2 ligand from the bicapped capsule, yielding a mono-capped Pd3Cu6L16L2 structure. Furthermore, the size of the anions critically influences the precise control over the post-synthetic modifications of the capsules. It was demonstrated that these capsules selectively encapsulate tetrahedral anions, offering a novel approach for the design of intelligent molecular delivery systems.

A CuI6L4 Cage Dynamically Reconfigures to Form Suit[4]anes and Selectively Bind Fluorinated Steroids

Simple organic ligands can self-assemble with metal ions to generate metal-organic cages, whose cavities bind guests selectively. This binding may enable new methods of chemical separation or sensing, among other useful functions. Here we report the preparation of a CuI6L4 pseudo-octahedral metal-organic cage, the ligands of which self-assemble from simple organic building blocks. Temperature, solvent, and the presence of different guests governed which structure predominated from a dynamic mixture of cage diastereomers with different arrangements of right- or left-handed metal vertices. Dissolution in dimethyl sulfoxide or the binding of tetrahedral guests led to a chiral tetrahedral T-symmetric framework, whereas low temperatures favored the achiral S4-symmetric diastereomer. Tetrahedral guests with long arms were encapsulated to form mechanically bonded suit[4]anes, with guest arms protruding out through host windows. The cage was also observed to bind fluorinated steroids, an important class of drug molecules, but not non-fluorinated steroids, providing the basis for new separation processes.

Coordination-Induced Emissive Poly-NHC-Derived Metallacage for Pesticide Detection

Developing sensitive, rapid, and convenient methods for the detection of residual toxic pesticides is immensely important to prevent irreversible damage to the human body. Luminescent metal-organic cages and macrocycles have shown great applications, and designing highly emissive supramolecular systems in dilute solution using metal-ligand coordination-driven self-assembly is demanded. In this study, we have demonstrated the development of a silver-carbene bond directed tetranuclear silver(I)-octacarbene metallacage [Ag4(L)2](PF6)4 (1) based on an aggregation-induced emissive (AIE) cored 1,1',1″,1‴-((1,4-phenylenebis(ethene-2,1,1-triyl))tetrakis(benzene-4,1-diyl))tetrakis(3-methyl-1H-imidazol-3-ium) salt (L). A 36-fold enhanced emission was observed after metallacage (1) formation when compared with the ligand (L) in dilute solution due to the restriction of intramolecular motions imparted by metal-ligand coordination. Such an increase in fluorescence made 1 a potential candidate for the detection of a broad-spectrum pesticide, 2,6-dichloro-nitroaniline (DCN). 1 was able to detect DCN efficiently by the fluorescence quenching method with a significant detection limit (1.64 ppm). A combination of static and dynamic quenching was applicable depending on the analyte concentration. The use of silver-carbene bond directed self-assembly to exploit coordination-induced emission as an alternative to AIE in dilute solution and then apply this approach to solve health and safety concerns is noteworthy and carries a lot of potential for future developments.

Recent Advances in Construction Strategies for Fluorescence Sensing Films

A year ago, film-based fluorescent sensors (FFSs) were recognized in the "IUPAC Top Ten Emerging Technologies in Chemistry 2022" due to their extensive application in detecting hidden explosives, illicit drugs, and volatile organic compounds. These sensors offer high sensitivity, specificity, immunity to light scattering, and noninvasiveness. The core of FFSs is the construction of high-performance fluorescent sensing films, which are dependent on the processes of "energy transfer" and "mass transfer" in the active layer and involve complex interactions between sensing molecules and analytes. This Perspective focuses on the latest strategies in constructing these films, emphasizing the design of sensing molecules with various innovative features and structures that enhance the mass transfer efficiency. Additionally, it discusses the ongoing challenges and potential advancements in the field of FFSs.

Construction and Hierarchical Self-Assembly of a Supramolecular Metal-Carbene Complex with Multifunctional Units

Hierarchical combinations involving metal-ligand interactions and host-guest interactions can consolidate building blocks with unique functions into material properties. This study reports the construction and hierarchical self-assembly of multifunctional trinuclear AuI tricarbene complex containing three crown ether units and three ferrocene units. Host-guest interactions between the multifunctional trinuclear AuI tricarbene complex and organic ammonium salts were investigated, revealing that crown ether-based host-guest interactions can effectively regulate the electrochemical properties of the complex. Utilizing bisammonium salt as the cross-linker and multifunctional trinuclear AuI tricarbene complex as the core, a stimuli-responsive and self-healing supramolecular gel with different functional units was obtained.

Diastereoselective Self-Assembly of Low-Symmetry Pdn L2n Nanocages through Coordination-Sphere Engineering

Metal-organic cages (MOCs) are popular host architectures assembled from ligands and metal ions/nodes. Assembling structurally complex, low-symmetry MOCs with anisotropic cavities can be limited by the formation of statistical isomer libraries. We set out to investigate the use of primary coordination-sphere engineering (CSE) to bias isomer selectivity within homo- and heteroleptic Pdn L2n cages. Unexpected differences in selectivities between alternative donor groups led us to recognise the significant impact of the second coordination sphere on isomer stabilities. From this, molecular-level insight into the origins of selectivity between cis and trans diastereoisomers was gained, highlighting the importance of both host-guest and host-solvent interactions, in addition to ligand design. This detailed understanding allows precision engineering of low-symmetry MOC assemblies without wholesale redesign of the ligand framework, and fundamentally provides a theoretical scaffold for the development of stimuli-responsive, shape-shifting MOCs.

Efficient manipulation of Förster resonance energy transfer through host-guest interaction enables tunable white-light emission and devices in heterotopic bisnanohoops

In this study, we synthesized and reported the heterotopic bisnanohoops P5-[8,10]CPPs containing cycloparaphenylenes (CPPs) and a pillar[5]arene unit, which act not only as energy donors but also as a host for binding energy acceptors. We demonstrated that a series of elegant FRET systems could be constructed successfully through self-assembly between donors P5-[8,10]CPPs and acceptors with different emissions via host-guest interaction. These FRET systems further allow us to finely adjust the donors P5-[8,10]CPPs and acceptors (BODIPY-Br and Rh-Br) for achieving multiple color-tunable emissions, particularly white-light emission. More importantly, these host-guest complexes were successfully utilized in the fabrication of white-light fluorescent films and further integrated with a 365 nm LED lamp to create white LED devices. The findings highlight a new application of carbon nanorings in white-light emission materials, beyond the common recognition of π-conjugated molecules.

Isoreticular Preparation of Tetraphenylethylene-based Multicomponent Metallacages towards Light-Driven Hydrogen Production

Multicomponent metallacages can integrate the functions of their different building blocks to achieve synergetic effects for advanced applications. Herein, based on metal-coordination-driven self-assembly, we report the preparation of a series of isoreticular tetraphenylethylene-based metallacages, which are well characterized by multinuclear NMR, ESI-TOF-MS and single-crystal X-ray diffraction techniques. The suitable integration of photosensitizing tetraphenylethylene units as faces and Re catalytic complexes as the pillars into a single metallacage offers a high photocatalytic hydrogen production rate of 1707 μmol g-1  h-1 , which is one of the highest values among reported metallacages. Femtosecond transient absorption and DFT calculations reveal that the metallacage can serve as a platform for the precise and organized arrangement of the two building blocks, enabling efficient and directional electron transfer for highly efficient photocatalytic performance. This study provides a general strategy to integrate multifunctional ligands into a certain metallacage to improve the efficiency of photocatalytic hydrogen production, which will guide the future design of metallacages towards photocatalysis.

Capture of Singlet Oxygen Modulates Host-Guest Behavior of Coordination Cages

The anthracene panels of two tetrahedral MII 4 L6 cages, where MII =CoII or FeII , were found to react with photogenerated singlet oxygen (1 O2 ) in a hetero-Diels-Alder reaction. ESI-MS analysis showed the cobalt(II) cages to undergo complete transformation of all anthracene panels into endoperoxides, whereas the iron(II) congeners underwent incomplete conversion. The reaction was found to be partially reversible in the case of the 1-FeII cage. The dioxygen-cage cycloadducts were found to bind a set of guest molecules more weakly than the parent cages, with affinity dropping by more than two orders of magnitude in some cases. The light-driven cycloaddition reaction between cage and 1 O2 thus served as a stimulus for guest release and reuptake.

Reversible and Turn-On Fluorescence Detection of Phosphate in Aqueous Solution and Living Cell Imaging by Supramolecular Metallacycles with AIE-Active Ligands

Luminescent supramolecular metallacycles have attracted great interest as a new promising class of sensing substrates. In this work, two tetraphenylethene (TPE)-based diimidazole and dipyrazole ligands with the aggregation-induced emission (AIE) feature were designed for the construction of supramolecular tetragonal metallacycles 1-4 with two 90° mononuclear [(bpy)M]2+ or dinuclear [(bpy)2M2]4+ acceptors (bpy = 2,2'-dipyridine; M = Pd, Pt), in which the fluorescence can be quenched to an "off" state due to the ligand-to-metal charge transfer (LMCT). Metallacycle 1 was utilized as a fluorescence sensor for phosphate (PO43-) detection in aqueous solution by means of disassembly, leading to the release of the ligand. Additionally, the metallacycle can be regenerated through self-assembly via the introduction of Pd(II) acceptors. PO43- was detected using TPE-based metallacycles over a wide concentration range, with a detection limit as low as 2.1 × 10-8 M. Furthermore, sensor 1 also presented the semiquantitative visual detection ability for PO43- in the test paper mode via fluorescence changes. The aforementioned studies not only enhance the current research on fluorescent materials but also offer a strategy for the creation of stimuli-responsive supramolecular coordination complexes.

Triphenylamine-Functionalized Coordination Cage as a Supramolecular Fluorescence Sensor for Sequential Detection of Aluminum Ions and Nitrofurantoin

Coordination cages with a well-defined nanocavity are a class of promising supramolecular materials for molecular recognition and sensing. However, their applications in sequential sensing of multiple types of pollutants are highly desirable yet extremely limiting and challenging. Herein, we demonstrate a convenient strategy to develop a supramolecular fluorescence sensor for sequentially detecting environmental pollutants of aluminum ions and nitrofurantoin. A coordination cage (Ni-NTB), adopting an octahedral structure with triphenylamine chromophores occupying on the faces, is weakly emissive in solution due to the intramolecular rotations of the phenyl rings. Ni-NTB exhibits sensitive and selective fluorescence "off-on-off" processes during consecutive sensing of Al³⁺ and nitrofurantoin, an antibacterial drug. These sequential detection processes are highly interference-tolerant and visually observable with the naked eye. Mechanism studies reveal that the fluorescence switch is controllable by tuning the degree of intramolecular rotations of the phenyl rings and the pathway of intermolecular charge transfer, which is associated with the host-guest interaction. Moreover, the fabrication of Ni-NTB on test strips enabled a quick naked-eye sequential sensing of Al³⁺ and nitrofurantoin in seconds. Hence, this novel supramolecular fluorescence "off-on-off" sensing platform provides a new approach to developing supramolecular functional materials for monitoring environmental pollution.

[2,2] Paracyclophanes-based double helicates for constructing artificial light-harvesting systems and white LED device

The construction of efficient artificial light-harvesting systems (ALHSs) is of vital importance in utilizing solar energy. Herein, we report the non-covalent syntheses of double helicates PCP-TPy1/2 and Rp,Rp-PCP-TPy1/2 by metal-coordination interaction and their applications in ALHSs and white light-emitting diode (LED) device. All double helicates exhibit significant aggregation-induced emission in tetrahydrofuran/water (1:9, v/v) solvent. The aggregated double helicates can be used to construct one-step or sequential ALHSs with fluorescent dyes Eosin Y (EsY) and Nile red (NiR) with the energy transfer efficiency up to 89.3%. Impressively, the PMMA film of PCP-TPy1 shows white-light emission when doped 0.075% NiR, the solid of double helicates (Rp,Rp-) PCP-TPy2 can be used as the additive of a blue LED bulb to achieve white-light emission. In this work, we provided a general method for the preparation of novel double helicates and explored their applications in ALHSs and fluorescent materials, which will promote future construction and application of helicates as emissive devices.

Photocatalysis in Water-Soluble Supramolecular Metal Organic Complex

As an emerging subset of organic complexes, metal complexes have garnered considerable attention owing to their outstanding structures, properties, and applications. In this content, metal-organic cages (MOCs) with defined shapes and sizes provide internal spaces to isolate water for guest molecules, which can be selectively captured, isolated, and released to achieve control over chemical reactions. Complex supramolecules are constructed by simulating the self-assembly behavior of the molecules or structures in nature. For this purpose, massive amounts of cavity-containing supramolecules, such as metal-organic cages (MOCs), have been extensively explored for a large variety of reactions with a high degree of reactivity and selectivity. Because sunlight and water are necessary for the process of photosynthesis, water-soluble metal-organic cages (WSMOCs) are ideal platforms for photo-responsive stimulation and photo-mediated transformation by simulating photosynthesis due to their defined sizes, shapes, and high modularization of metal centers and ligands. Therefore, the design and synthesis of WSMOCs with uncommon geometries embedded with functional building units is of immense importance for artificial photo-responsive stimulation and photo-mediated transformation. In this review, we introduce the general synthetic strategies of WSMOCs and their applications in this sparking field.

Real-Time Temperature Sensing Using a Ratiometric Dual Fluorescent Protein Biosensor

Accurate temperature control within biological and chemical reaction samples and instrument calibration are essential to the diagnostic, pharmaceutical and chemical industries. This is particularly challenging for microlitre-scale reactions typically used in real-time PCR applications and differential scanning fluorometry. Here, we describe the development of a simple, inexpensive ratiometric dual fluorescent protein temperature biosensor (DFPTB). A combination of cycle three green fluorescent protein and a monomeric red fluorescent protein enabled the quantification of relative temperature changes and the identification of temperature discrepancies across a wide temperature range of 4-70 °C. The maximal sensitivity of 6.7% °C^-1 and precision of 0.1 °C were achieved in a biologically relevant temperature range of 25-42 °C in standard phosphate-buffered saline conditions at a pH of 7.2. Good temperature sensitivity was achieved in a variety of biological buffers and pH ranging from 4.8 to 9.1. The DFPTB can be used in either purified or mixed bacteria-encapsulated formats, paving the way for in vitro and in vivo applications for topologically precise temperature measurements.

Tetramine Aspect Ratio and Flexibility Determine Framework Symmetry for Zn8 L6 Self-Assembled Structures

We derive design principles for the assembly of rectangular tetramines into Zn8 L6 pseudo-cubic coordination cages. Because of the rectangular, as opposed to square, geometry of the ligand panels, and the possibility of either Δ or Λ handedness of each metal center at the eight corners of the pseudo-cube, many different cage diastereomers are possible. Each of the six tetra-aniline subcomponents investigated in this work assembled with zinc(II) and 2-formylpyridine in acetonitrile into a single Zn8 L6 pseudo-cube diastereomer, however. Each product corresponded to one of four diastereomeric configurations, with T, Th , S6 or D3 symmetry. The preferred diastereomer for a given tetra-aniline subcomponent was shown to be dependent on its aspect ratio and conformational flexibility. Analysis of computationally modeled individual faces or whole pseudo-cubes provided insight as to why the observed diastereomers were favored.

Artificial Light-Harvesting System Based on Zinc Porphyrin and Benzimidazole: Construction, Resonance Energy Transfer, and Amplification Strategy for Electrochemiluminescence

Constructing robust and efficient luminophores is of significant importance in the development of electrochemiluminescence (ECL) amplification strategies. Inspired by the resonance energy transfer in natural light-harvesting systems, we propose a novel ECL amplification system based on ECL resonance energy transfer (ECL-RET), which integrates two luminophores, benzimidazole (BIM) and zinc(II) tetrakis(4-carboxyphenyl)porphine (ZnTCPP), into one framework. Through disassembling and reconstruction processes, numerous BIM surround ZnTCPP in the constructed ZIF-9-ZnTCPP. Combined with the overlapped spectra between the emission of BIM and the absorption of ZnTCPP, the energy of multiple BIM (donor) can be concentrated to a single ZnTCPP (acceptor) to amplify the ECL emission of the acceptor. This work provides a convenient way to design an efficient ECL-RET system, which initiates a brand-new chapter in the development of ECL amplification strategies.

Solvato-Controlled Assembly and Structural Transformation of Emissive Poly-NHC-Based Organometallic Cages and Their Applications in Amino Acid Sensing and Fluorescence Imaging

Stimuli-induced structural transformation of supramolecular cages has drawn increasing attention because of their sensitive feature to external variations as model systems to simulate biological processes. However, combining structural transformation and useful functions has remained a difficult task. This study reports the solvato-controlled self-assembly of two unique topologies with different emission characteristics, a water-soluble Ag₈ L₄ cage (A) and an Ag₄ L₂ cage (B), produced from the same sulfonate-pendant tetraphenylethene (TPE) bridged tetrakis-(1,2,4-triazolium) ligand. Both cages show interesting solvent-responsive reversible structural transformation, and the change of fluorescence signals can efficiently track the process. Additionally, water-soluble cage A exhibits unique properties in thermochromism, thiol amino acid sensing, and subcellular imaging in aqueous media.

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.

Hexaphenyltriphenylene-Based Multicomponent Metallacages: Host-Guest Complexation for White-Light Emission

A hexaphenyltriphenylene-based hexatopic pyridyl ligand is designed and used to prepare three hexagonal prismatic metallacages via metal-coordination-driven self-assembly. Owing to the planar conjugated structures of the hexaphenyltriphenylene skeleton, such metallacages show good host-guest complexation with a series of emissive dyes, which have been further used to tune their emission in solution. Interestingly, based on their complementary emission colors, white light emission is achieved in a mixture of the host metallacages and the guests.

Trefoil-Shaped Metal-Organic Cages as Fluorescent Chemosensors for Multiple Detection of Fe3+, Cr2O72-, and Antibiotics

The construction of metal-organic cages (MOCs) with specific structures and fluorescence sensing properties is of much importance and challenging. Herein, a novel phenanthroline-based metal-organic cage, [Cd₃L₃·6MeOH·6H₂O] (1), was synthesized by metal-directed assembly of the ligand 3,3'-[(1E,1'E)-(1,10-phenanthroline-2,9-diyl)bis(ethene-2,1-diyl)]dibenzoic acid (H₂L) and CdI₂ using a solvothermal method. According to single-crystal X-ray analysis, cage 1 exhibits a rare trefoil-shaped structure. Meanwhile, the discrete MOCs are further stacked into a 3D porous supramolecular structure through abundant intermolecular C-H···O interactions. Additionally, through exploration of fluorescence sensing on cations, anions, and antibiotics in aqueous solution, the experimental results indicate that cage 1 has excellent fluorescence sensing abilities for Fe³⁺, Cr₂O₇^2-, and nitrofuran and nitroimidazole antibiotics. The sensing ability of 1 remains unaltered for five cycles toward all analytes. The above results suggested that cage 1 can be considered a potential multiple sensor for the detection of Fe³⁺, Cr₂O₇^2-, and some antibiotics.

Recent progress on small molecular temperature-sensitive fluorescent probes

Temperature is an important biophysical parameter that is closely related with the metabolic activity in living cells. Therefore, the detection of intracellular temperature changes is crucial for exploring temperature-related biological processes. Fluorescence probe is an ideal tool for observing temperature changes in cells, which has many advantages, such as high sensitivity, good selectivity, and noninvasive, and thus aroused the great interest of researchers. In this paper, we summarize the recent progress of organic small molecule temperature-sensitive fluorescence probes in recent years was reviewed. Particularly, we describe the common response mode to the temperature and the practical applications of the probe in living cells and even animal models. Moreover, an outlook regarding temperature detection in clinical applications is discussed. The temperature-sensitive fluorescent probe is a "black box" to many researchers. This review aims to open a window on the prospect of the noninvasive in vivo detection of temperature which is helpful to deeper understand this rich research area.

Spin Crossover Induced by Changing the Identity of the Secondary Metal Ion from PdII to NiII in a Face-Centered FeII 8 MII 6 Cubic Cage

Discrete spin crossover (SCO) heteronuclear cages are a rare class of materials which have potential use in next-generation molecular transport and catalysis. Previous investigations of cubic cage [Fe₈ Pd₆ L₈ ]²⁸⁺ constructed using semi-rigid metalloligands, found that Fe^II centers of the cage did not undergo spin transition. In this work, substitution of the secondary metal center at the face of the cage resulted in SCO behavior, evidenced by magnetic susceptibility, Mössbauer spectroscopy and single crystal X-ray diffraction. Structural comparisons of these two cages shed light on the possible interplay of inter- and intramolecular interactions associated with SCO in the Ni^II analogue, 1 ([Fe₈ Ni₆ L₈ (CH₃ CN)₁₂ ]²⁸⁺ ). The distorted octahedral coordination environment, as well as the occupation of the CH₃ CN in the Ni^II axial positions of 1, prevented close packing of cages observed in the Pd^II analogue. This led to offset, distant packing arrangements whereby important areas within the cage underwent dramatic structural changes with the exhibition of SCO.

Complementarity and Preorganisation in the Assembly of Heterometallic–Organic Cages via the Metalloligand Approach—Recent Advances

The design of new metallocage polyhedra towards pre-determined structures can offer both practical as well as intellectual challenges. In this mini-review we discuss a selection of recent examples in which the use of the metalloligand approach has been employed to overcome such challenges. An attractive feature of this approach is its stepwise nature that lends itself to the design and rational synthesis of heterometallic metal–organic cages, with the latter often associated with enhanced functionality.

Development of a multiplexing potency assay using upconverting nanoparticles-based luminescence resonance energy transfer

A homogeneous particle-based immunoassay using upconverting nanoparticles (UCNPs) has been developed for multiplexing potency analysis of two different therapeutic monoclonal antibodies (mAbs) in a fixed-combination formulation.The UCNP, considered as the best donor lumiphore for luminescence resonance energy transfer (LRET), offers long lasting excitation state and increased signal-to-noise (S/N) ratio due to low autofluorescence effect and light scattering from near infrared (NIR) excitation. In this study, the dose-response curves for each therapeutic mAb were generated using two distinct UCNPs. This proof-of-concept LRET-based immunoassay demonstrated a novel approach for increasing testing throughput and analyzing the potency of mixed therapeutic mAbs in co-formulated products.

Morpholine-Functionalized Multicomponent Metallacage as a Vector for Lysosome-Targeted Cell Imaging

Metallacages with suitable cavities and specific functions are promising delivery vectors in biological systems. Herein, we report a morpholine-functionalized metallacage for lysosome-targeted cell imaging. The efficient host-guest interactions between the metallacage and dyes prevent them from aggregation, so their emission in aqueous solutions is well maintained. The fluorescence quantum yield of these host-guest complexes reaches 74.40%. Therefore, the metallacage is further employed as a vector to deliver dyes with different emission colors (blue, green, and red) into lysosomes for targeted imaging. This research affords a type of vector for the delivery of various cargos toward biological applications, which will enrich the usage of metallacages in biomedical engineering.

Highly Efficient Sky-Blue π-Stacked Thermally Activated Delayed Fluorescence Emitter with Multi-Stimulus Response Properties

Organic materials with multi-stimulus response (MSR) properties have demonstrated many potential and practical applications. Herein, a π-stacked thermally activated delayed fluorescence (TADF) material with multi-stimulus response (MSR) properties, named SDMAC, was designed and synthesized using distorted 9,9-dimethyl-10-phenyl-9,10-dihydroacridine as a donor. SDMAC possesses a rigid π-stacked configuration with intramolecular through-space interactions and exhibits aggregation-induced emission enhancement (AIEE), solvatochromic, piezochromic, and circularly polarized luminescence (CPL) under different external stimuli. The rigid molecular structure and efficient TADF properties of SDMAC can be used in displays and lighting. Using SDMAC as an emitter, the maximum external quantum efficiency (EQE) of the fabricated organic light-emitting diodes (OLEDs) is as high as 28.4 %, which make them the most efficient CP-TADF OLEDs based on the through-space charge transfer strategy. The CP organic light-emitting diodes (CP-OLEDs) exhibit circularly polarized electroluminescence (CPEL) signals.

Hexaphenylbenzene-Based Deep Blue-Emissive Metallacages as Donors for Light-Harvesting Systems

We herein report the preparation of a series of hexaphenylbenzene (HPB)-based deep blue-emissive metallacages via multicomponent coordination-driven self-assembly. These metallacages feature prismatic structures with HPB derivatives as the faces and tetracarboxylic ligands as the pillars, as evidenced by NMR, mass spectrometry and X-ray diffraction analysis. Light-harvesting systems were further constructed by employing the metallacages as the donor and a naphthalimide derivative (NAP) as the acceptor, owing to their good spectral overlap. The judiciously chosen metallacage serves as the antenna, providing the suitable energy to excite the non-emissive NAP, and thus resulting in bright emission for NAP in the solid state. This study provides a type of HPB-based multicomponent emissive metallacage and explores their applications as energy donors to light up non-emissive fluorophores in the solid state, which will advance the development of emissive metallacages as useful luminescent materials.

Reversible Multielectron Release from Redox-Active Three-Dimensional Molecular Barrels with Ruthenium-Alkenyl Moieties

Three-dimensional molecular barrels Ru₆-4 and Ru₆-5 were synthesized in high yields from dinuclear ruthenium-vinyl clamps and tritopic triphenylamine-derived carboxylate linkers and characterized by multinuclear NMR spectroscopy including ¹H-¹H COSY and ¹H DOSY measurements, high-resolution electrospray ionization mass spectrometry, and X-ray crystallography. The metal frameworks of the cages adopt the shape of twisted trigonal prisms, and they crystallize as racemic mixtures of interdigitating Δ- and Λ-enantiomers with a tight columnar packing in Ru₆-4. Electrochemical studies and redox titrations revealed that the cages are able to release up to 11 electrons on the voltammetric timescale and that their cage structures persist up to the hexacation level. IR and UV-vis-near-infrared spectroelectrochemical studies confirm substituent-dependent intramolecular electronic communication within the π-conjugated 1,3-divinylphenylene backbone in the tricationic states, where all three divinylphenylene-bridged diruthenium clamps are present in mixed-valent radical cation states. The formation of 1:3 charge-transfer salts with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane as the electron acceptor is also demonstrated.

Modifying the internal substituents of self-assembled cages controls their molecular recognition and optical properties

Self-assembled Fe₄L₆ cage complexes with variable internal functions can be synthesized from a 2,7-dibromocarbazole ligand scaffold, which orients six functional groups to the cage interior. Both ethylthiomethylether and ethyldimethylamino groups can be incorporated. The cages show strong ligand-centered fluorescence emission and a broad range of guest binding properties. Coencapsulation of neutral organic guests is favored in the larger, unfunctionalized cage cavity, whereas the thioether cage has a more sterically hindered cavity that favors 1 : 1 guest binding. Binding affinities up to 10⁶ M^-1 in CH₃CN are seen. The dimethylamino cage is more complex, as the internal amines display partial protonation and can be deprotonated by amine bases. This amine cage displays affinity for a broad range of neutral organic substrates, with affinities and stoichiometries comparable to that of the similarly sized thioether cage. These species show that simple variations in ligand backbone allow variations in the number and type of functions that can be displayed towards the cavity of self-assembled hosts, which will have applications in biomimetic sensing, catalysis and molecular recognition.

Porphyrin-Based Multicomponent Metallacage: Host-Guest Complexation toward Photooxidation-Triggered Reversible Encapsulation and Release

The development of supramolecular hosts with effective host-guest properties is crucial for their applications. Herein, we report the preparation of a porphyrin-based metallacage, which serves as a host for a series of polycyclic aromatic hydrocarbons (PAHs). The association constant between the metallacage and coronene reaches 2.37 × 10⁷ M^-1 in acetonitrile/chloroform (ν/ν = 9/1), which is among the highest values in metallacage-based host-guest complexes. Moreover, the metallacage exhibits good singlet oxygen generation capacity, which can be further used to oxidize encapsulated anthracene derivatives into anthracene endoperoxides, leading to the release of guests. By employing 10-phenyl-9-(2-phenylethynyl)anthracene whose endoperoxide can be converted back by heating as the guest, a reversible controlled release system is constructed. This study not only gives a type of porphyrin-based metallacage that shows desired host-guest interactions with PAHs but also offers a photooxidation-responsive host-guest recognition motif, which will guide future design and applications of metallacages for stimuli-responsive materials.

Self-assembled Pt(II) metallacycles enable precise cancer combination chemotherapy

Coadministration of drug molecules in adequate combinations for cancer treatment reduces the doses of each constituent, overcomes resistance mechanisms, and reduces the influence of tumor heterogeneity. Here we utilize coordination-driven self-assembly to prepare platinum(II) metallacycles comprising two drug molecules with distinct anticancer mechanisms in precise ratios. Nanoformulations fabricated by encapsulating the metallacycles into amphiphilic diblock copolymers efficiently enter cancer cells and release the active drug molecules at the exact loading ratio in the reductive cancer microenvironments, leading to a synergistic anticancer effect and therefore a favorable treatment outcome. This study provides a promising supramolecular methodology for the precise organization and delivery of bioactive molecules for inducing synergistic biological effects that maximize therapeutic efficacy.

Combination chemotherapy, which involves the simultaneous use of multiple anticancer drugs in adequate combinations to disrupt multiple mechanisms associated with tumor growth, has shown advantages in enhanced therapeutic efficacy and lower systemic toxicity relative to monotherapy. Herein, we employed coordination-driven self-assembly to construct discrete Pt(II) metallacycles as monodisperse, modular platforms for combining camptothecin and combretastatin A4, two chemotherapy agents with a disparate mechanism of action, in precise arrangements for combination chemotherapy. Formulation of the drug-loaded metallacycles with folic acid–functionalized amphiphilic diblock copolymers furnished nanoparticles with good solubility and stability in physiological conditions. Folic acids on the surface of the nanoparticles promote their internalization into cancer cells. The intracellular reductive environment of cancer cells induces the release of the drug molecules at an exact 1:1 ratio, leading to a synergistic anticancer efficacy. In vivo studies on tumor-bearing mice demonstrated the favorable therapeutic outcome and minimal side effects of the combination chemotherapy approach based on a self-assembled metallacycle.

A Redox-Active Supramolecular Fe4L6 Cage Based on Organic Vertices with Acid-Base-Dependent Charge Tunability for Dehydrogenation Catalysis

Supramolecular cage chemistry is of lasting interest because, as artificial blueprints of natural enzymes, the self-assembled cage structures not only provide substrate-hosting biomimetic environments but also can integrate active sites in the confined nanospaces for function synergism. Herein, we demonstrate a vertex-directed organic-clip chelation assembly strategy to construct a metal-organic cage Fe₄L₆⁸⁺ (MOC-63) incorporating 12 imidazole proton donor-acceptor motifs and four redox-active Fe centers in an octahedral coordination nanospace. Different from regular supramolecular cages assembled with coordination metal vertices, MOC-63 comprises six ditopic organic-clip ligands as vertices and four tris-chelating Fe(N∩N)₃ moieties as faces, thus improving its acid, base, and redox robustness by virtue of cage-stabilized dynamics in solution. Improved dehydrogenation catalysis of 1,2,3,4-tetrahydroquinoline derivatives is accomplished by MOC-63 owing to a supramolecular cage effect that synergizes multiple Fe centers and radical species to expedite intermediate conversion of the multistep reactions in a cage-confined nanospace. The acid-base buffering imidazole motifs play a vital role in modulating the total charge state to resist pH variation and tune the solubility among varied solvents, thereby enhancing reaction acceleration in acidic conditions and rendering a facile recycling catalytic process.