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Supramolecular coordination complexes (SCCs) are predictable and size-tunable supramolecular self-assemblies constructed through directional coordination bonds between readily available organic ligands and metallic receptors. Based on planar and 3D structures, SCCs can be mainly divided into two categories: metallacycles (e.g., rhomboidal, triangular, rectangular, and hexagonal) and metallacages (e.g., tetrahedral, hexahedral, and dodecahedral). The directional coordination bonds enable the efficient formation of metallacycles and metallacages with well-defined architectures and geometries. SCCs exhibit several advantages, including good directionality, strong interaction force, tunable modularity, and good solution processability, making them highly attractive for biomedical applications, especially in cellular imaging and cancer therapy. Compared with their molecular precursors, SCCs demonstrate enhanced cellular uptake and a strengthened tumor accumulation effect, owing to their inherently charged structures. These properties and the chemotherapeutic potential inherent to organic platinum complexes have promoted their widespread application in antitumor therapy. Furthermore, the defined structures of SCCs, achieved viathe design modification of assembly elements and introduction of different functional groups, enable them to combat malignant tumors through multipronged treatment modalities. Because the development of cancer-treatment methodologies integrated in clinics has evolved from single-modality chemotherapy to synergistic multimodal therapy, the development of functional SCCs for synergistic cancer therapy is crucial. While some pioneering reviews have explored the bioapplications of SCCs, often categorized by a specific function or focusing on the specific metal or ligand types, a comprehensive exploration of their synergistic multifunctionality is a critical gap in the current literature.

A new class of 120° dendritic di-Pt(II) acceptor subunits has been designed and synthesized, from which six-component hexagonal metallodendrimers were easily formed with 120° dendritic dipyridine donors via [3 + 3] coordination-driven self-assembly. The structures of all metallodendrimers are confirmed by multinuclear NMR, ESI-TOF-MS/ESI-FTMS, and elemental analysis. MMFF force-field simulations indicates that all metallodendrimers have a hexagonal ring with an internal radius of approximately 1.4 nm.

The self-assembly of irregular metallo-supramolecular hexagons and parallelograms has been achieved in a self-selective manner upon mixing 120° unsymmetrical dipyridyl ligands with 60° or 120° organoplatinum acceptors in a 1:1 ratio. The polygons have been characterized using 31P and 1H multinuclear NMR spectroscopy and electrospray ionization mass spectrometry (ESI-MS) as well as X-ray crystallography. Geometric features of the molecular subunits direct the self-selection process, which is supported by molecular force field computations.

Supramolecular coordination complexes formed by coordination-induced assembly not only avoid the loss of activity of precursors but also provide an efficient way for controlled release, which can be further used in various fields of biology such as drug delivery, cell imaging, and tumor treatment. In this work, a PtIImetallaclip (4) was prepared from 4-[4-(1,2,2-triphenylvinyl)phenyl]pyridine (1), 5,10,15-triphenyl-20-(pyridin-4-yl)porphyrin (2), 90oPt, and glycol-chain-modified isophthalic acid (3) in an acetone/water mixture through the “coordination-driven self-assembly” method. 31P and 1H NMR spectroscopy and high-resolution mass spectrometry were used to characterize the obtained metallaclip 4. 4can self-assemble into fluorescent nanostructures in aqueous solution because of the tetraphenylethylene unit and its amphiphilic nature. Importantly, the fluorescent nanoparticles not only can be employed for cell imaging but also can generate singlet oxygen (1O2) under 660 nm laser irradiation and the release of Ptdrug in the tumor issue for cancer therapy. The work may provide a new way for scientists to construct functional biomaterials with multiple applications via molecular self-assembly.

Enzyme-responsive nanomaterials are emerging as important candidates for bioanalytical and biomedical applications due to their good biocompatibilities and sensitivities. However, the lack of promising operation platforms compatible with enzyme responsiveness greatly limits the scope and functionality of smart materials. Herein, we report the design and synthesis of a naphthalene-functionalized organoplatinum(II) metallacycle 1by means of coordination-driven self-assembly, which is subsequently exploited as the organometallic platform to enable enzyme-responsive supramolecular materials. Specifically, a [2 + 2] self-assembled metallacycle 1first self-assembles into nanosheets in aqueous solution, which can further transform into vesicles with the introduction of β-cyclodextrin (β-CD) because of the formation of a bola-type supramolecular amphiphile β-CD-1. Interestingly, these vesicles show rare α-amylase responsiveness, as demonstrated by structurally transforming back into nanosheets after the addition of α-amylase to their solutions due to the enzyme-induced degradation of cyclodextrins. We also demonstrate the potential application of the self-assembled vesicles in amylase-responsive controlled release.

Materials with aggregation-induced emission (AIE) properties are of growing interest due to their widespread applications. AIEgens, such as tetraphenylethylene units, display varying emission behaviors during their conformational changes. However, the structure–property relationships of the intermediate conformations have rarely been explored. Herein, we show that the conformational restriction on TPE units can affect the structural relaxation in the excited state and the resulting photophysical behaviors. Specifically, three metallacages of different sizes were prepared via the coordination-driven self-assembly of a TPE-based tetrapyridyl donor with length-increasing Pt(II) acceptors. While the metallacages share similar scaffolds, they exhibit a trend of red-shifted fluorescence and attenuated quantum yield with the increase of their sizes. Furthermore, spectroscopic and computational studies together with a control experiment were conducted, revealing that the degree of cage tension imposed on the excited-state conformational relaxation of TPE moieties resulted in their distinct photophysical properties. The precise control of conformation holds promise as a strategy for understanding the AIE mechanism as well as optimizing the photophysical behaviors of materials on the platform of supramolecular coordination complexes.

Two trigonal prismatic metallacages 1and 2bearing triphenylamine and anthracene moieties are designed and synthesized to fabricate artificial light-harvesting systems (LHSs). These two cages are prepared via the coordination-driven self-assembly of two anthracene–triphenylamine-based tripyridyl ligand 3, three dicarboxylates, and six 90° Pt(II) acceptors. The design of the anthracene–triphenylamine chromophore makes possible the tunable excited-state property (like the emissive transition energy and lifetime) as a function of the solvent polarity, temperature, and concentration. The synergistic photophysical footprint of these metallacages, defined by their high absorptivity and emission quantum yield (QY) relative to the free ligand 3, signifies them as a superior light sensitizer component in an LHS. In the presence of the fluorescent dye Nile Red (NR) as an energy acceptor, the metallacages display efficient (>93%) excited energy transfer to NR through an apparent static quenching mechanism in viscous dimethyl sulfoxide solvent.

The accurate control of multicomponent self-assembly to fabricate a single assembly is still a challenge. Herein we describe multicomponent coordination-driven self-assembly with appropriately designed stoichiometric ratios to control the formation of fused C3vpolygons. Each of the assemblies involves two donors and one acceptor molecule, combined in the proper ratios assembling to give two rhomboidal trefoils and two triangular trefoils. The structures were characterized by 1H NMR, 31P NMR, 1H–1H NOESY NMR, DOSY NMR, ESI-MS, DLS, and TEM. Both the rhomboidal trefoils and triangular trefoils exhibit flat conformations on the basis of their calculated structures.

Despite rapid progress in recent years, it has remained challenging to prepare well-defined metal–organic complex-based suprastructures. As a result, the physicochemical mechanisms leading to their geometrical complexity remain perplexing. Here, a porphyrin-based metallacage was used as a building block to construct octahedra via self-assembly, and the mechanism for the evolution of the metallacages into octahedra was disclosed by both experiments and theoretical simulations.

Chiral metal–organic complexes hold great promise as new functional materials that exhibit unique stereochemical and optical properties. Here, we report the formation of optically pure pillar[5]arene-based platinum chiral metallacycles. By coordination with 60° and 90° Pt(II) acceptors, planar chiral platinum triangles were self-assembled efficiently and characterized by multiple spectroscopic techniques. Optical studies indicated that these metallacycles had chiral properties: pSenantiomers showed a negative Cotton effect, and pRenantiomers exhibited a positive Cotton effect. In addition, these metallacycles also exhibited circularly polarized luminescence.

Coordination-driven Pt metallacycles have shown potential in controllable modular self-assembly, which has made a vital contribution to biomedicine, catalysis, and multiresponsive materials. Herein, pillar[5]arene units were integrated into one skeleton through coordination-driven self-assembly, resulting in the formation of a hexagonal Pt(II) metallacycle decorated with six pillar[5]arenes. The host–guest interactions of the as-prepared metallacycle (pillar[5]arenes as hosts) and 1-butyl-4-[4-(diphenylamino)styryl]pyridinium (guest) were investigated. The metallacycle was found to facilitate the coaggregation between the guests and pillar[5]arenes through a synergistic effect, thus engendering a sharp increase in fluorescence intensity. The resultant aggregate was investigated by DLS and TEM. Our studies imply that the pillar[5]arene-containing metallacycle can serve as a potential platform for realizing emission enhancement effects.

Poor processability of fullerenes is a major remaining drawback for them to be studied monomolecularly and to find real-life applications. One of the strategies to tackle this problem is to encapsulate them within a host, which is however quite often, accompanied by significant alteration of their physical/chemical properties as encountered in chemical modification. To minimize the effect, an electron-deficient entities-based, dissolvable, and fluorescence active supramolecular host was designed and constructed via coordination-driven self-assembly of o-tetrapyridyl perylene bisimide (PBI) with cis-(PEt3)2Pt(OTf)2. The trigonal prism 1possesses a trigonal-prismatic inner cavity with 14.7 Å as the diameter of its inscribed circle. Host–guest chemistry investigations revealed that both C60and C70could be quantitatively encapsulated by the host in a 1:1 ratio. Further studies demonstrated that the produced host–guest complex 1⊃C70is significantly more stable than 1⊃C60, allowing complete transformation of the latter to the former and separation of C70from its mixture with C60. The fullerenes in the inclusion state could rotate freely within the cavity. Electrochemistry and spectroscopy studies disclosed that the encapsulation of the guests shows little effect upon the reduction of the host and its fluorescence properties. Thus, “like dissolves like” is believed to be the main driving force for the formation of the host–guest complexes. Moreover, the host and host–guest complexes can be fabricated into monomolecular membranes using the conventional Langmuir–Blodgett technique. We propose that these unique host–guest complexes could be used as model ensembles for further studies of the physical/chemical properties of fullerenes in both single molecular and 2D membrane states. In addition, their reversible four-electron reduction property may allow them to find applications in photo/electrocatalysis, organic electronics, etc.

The utilization of structural water in chemical self-assembly has not only effectively eliminated the negative influences of solvents from solutions or gels but has also provided new insight into the fabrication of new materials in bulk. However, up to now, supramolecular polymerization triggered by structural water has been dominated more by serendipity than rational design. After carefully analyzing the chemical structures of artificial monomers and gaining a deep understanding of the water-triggered assembly process, we report herein the bulk formation of polymeric materials from water and low-molecular weight monomers by rational design instead of serendipity.

Hierarchical self-assembly of discrete organoplatinum(II) metallacycles has attracted considerable attention. However, the exact assembly mechanism involving non-covalent interactions has limited the formation and application of self-assembly due to the dynamics of platinum metallacycles. Herein, we report the hierarchical self-assembly of a pyrene-based discrete organoplatinum(II) double-metallacycle that takes advantage of heteroligation-coordination-driven self-assembly and triflate anions' hydrogen bonding, which is extended into a 3-D supramolecular framework by the hydrogen-bonding interactions involving triflate anions. Furthermore, the assembled system displays tunable fluorescence emission and enhanced solid emission. The studies herein disclosed pave the way to prepare platinum(II) metallacycle-based supramolecular functional materials.

Introducing self-assembly strategies into the construction of catalysts has been proven to have great advantages in asymmetric catalysis. We constructed two chiral metalla-triangles by highly efficient coordination-driven self-assembly from a chiral 3,3′-dipyridyl-substituted BINOL donor. They were successfully applied in asymmetric conjugate addition of a series of α,β-unsaturated ketones with trans-styrylboronic acids. The use of these metalla-triangles as supramolecular catalysts is obviously conducive to the enhancement of catalytic activity and stereoselectivity in the presented addition reactions. Under induction of the chiral metalla-triangles, an array of α,β-enones were converted to chiral γ,δ-unsaturated ketones in medium to quantitative yields (40–98%) with high enantioselectivities (87–96% ee).

Post-assembly modification is a useful tool for producing discrete metallasupramolecular structures. However, the simple structural transformation by facile covalent reactions greatly impedes the development of functional organometallic materials. Herein, we describe the successful outcome by means of coordination-driven self-assembly and post-assembly reversible addition–fragmentation chain-transfer polymerization in preparing an amphiphilic supramolecular block copolymer Pt-PBEMA-b-POEGMApossessing H2O2-responsive diblock copolymers arms and a well-defined metallacycle core. The polymer self-assembles into nanoparticles (Pt NPs), which are able to encapsulate palmitoyl ascorbate (PA) and doxorubicin (DOX). After being internalized by cancer cells, PA serves as a prooxidant to elevate the H2O2concentration through cascade reactions to reverse the amphiphilicity of Pt-PBEMA-b-POEGMAthrough a H2O2-responsive removal of the hydrophobic domains, thus promoting the release of DOX. Meanwhile, the released quinone methide depletes the intracellular glutathione to decrease the antioxidation ability of cancer cells, realizing synergistic anticancer efficacy. Due to the sophisticated design and the enhanced permeability and retention effect, the nanomedicine codelivering PA and DOX highly accumulates in the tumor site. In vitro and in vivo results show the excellent antitumor performance of Pt NPs@PA/DOX, which greatly suppresses tumor growth after intravenous administration with negligible systemic toxicity.

Stimuli-responsive complexes have attracted significant interest in supramolecular chemistry and material science. In this study, a new organoplatinum–crown supramolecular complex has been successfully constructed via the coordination of benzo-21-crown-7 (B21C7) units and cis-Pt(PEt3)2(OTf)2. The resulting complex displays intriguing lower critical solution temperature (LCST) and anion-sensitive deassembly behavior. This organoplatinum–crown ether complex with dual-responsive behavior is a promising candidate for stimuli-responsive materials.

In this report, we describe the synthesis of two porphyrin-containing Pt(II) supramolecular assemblies via coordination-driven self-assembly. X-ray crystallographic analysis on one assembly reveals that the metalla-assembly formation imposes large interchromophore distances, leading to a higher 1O2generation efficiency, relative to the corresponding small molecular precursors. The metalla-assemblies were examined as photosensitizers for photodynamic therapy as the potential reduction of the unfavorable self-aggregation phenomenon. In vivo and in vitro investigations demonstrate that the metalla-assemblies exhibit enhanced anticancer activity with minimal dose requirement and side effects comparable to the small molecule precursors. Thus, our work demonstrates that self-assembly provides a promising methodology for enhancing the therapeutic effectiveness of anticancer agents.

Singlet oxygen (1O2), as an important active reagent, has found wide applications in photodynamic therapy (PDT), synthetic chemistry, and materials science. Organic conjugated aromatics serving as hosts to capture and release singlet oxygen have been systematically investigated over the last decades. Herein, we present a [6 + 6] organoplatinum(II) metallacycle by using ∼180° dipyridylanthracene donor and ∼120° Pt(II) acceptor as the building blocks, which enables the capture and release of singlet oxygen with relatively high photooxygenation and thermolysis rate constants. The photooxygenation of the metallacycle to the corresponding endoperoxide was performed by sensitized irradiation, and the resulting endoperoxide is stable at room temperature and can be stored under ambient condition over months. Upon simple heating of the neat endoperoxide under inert atmosphere at 120 °C for 4 h, the resulting endoperoxide can be reconverted to the corresponding parent form and singlet oxygen. The photooxygenation and thermolysis products were characterized by NMR spectroscopy and electrospray ionization time-of-flight mass spectrometric analysis. Density functional theory calculations were conducted in order to reveal the frontier molecular orbital interactions and reactivity. This work provides a new material platform for singlet oxygen related promising applications.

Control over the stimuli-responsive behavior of smart molecular systems can influence their capability to execute complex functionalities. Herein, we report the development of a suite of spiropyran-based multi-stimuli-responsive self-assembled platinum(II) macrocycles (5–7), rendering coordination-assisted enhanced photochromism relative to the corresponding ligands. 5showed shrinking and swelling during photoreversal, while 6and 7are fast and fatigue-free supramolecular photoswitches. 6turns out to be a better fatigue-resistant photoswitch and can retain an intact photoswitching ability of up to 20 reversible cycles. The switching behavior of the macrocycles can also be precisely controlled by tuning the pH of the medium. Our present strategy for the construction of rapid stimuli-responsive supramolecular architectures via coordination-driven self-assembly represents an efficient route for the development of smart molecular switches.

The dianthracene-based rhomboidal organoplatinum(II) metallacycle 1was successfully obtained via coordination-driven self-assembly involving the combination of diplatinum(II) acceptor 2and dipyridyl donor 3. A dilute acetone solution of the prepared metallacycle exhibited temperature-responsive fluorescence involving a gradual red-shifted fluorescent change from cyan to yellow over a wide temperature range from 77 to 297 K. Notably, a linear correlation was observed between the emission maximum and temperature in the low-temperature region from 77 to 137 K. Additionally, the supramolecular coordination complex in the solid state showed reversible mechanochromic fluorescence behavior with an obvious color change between green and yellow. Further investigation revealed that a morphology change before and after grinding was responsible for the observed mechanofluorochromic phenomenon. These studies provide new insight into the preparation of well-defined supramolecular organoplatinum(II) metallacycles capble of responding to multiple stimuli.

Here, we present a method for the building of new bicyclic heterometallic cross-linked supramolecular polymers by hierarchical unification of three types of orthogonal noncovalent interactions, including platinum(II)–pyridine coordination-driven self-assembly, zinc–terpyridine complex, and host–guest interactions. The platinum–pyridine coordination provides the primary driving force to form discrete rhomboidal metallacycles. The assembly does not interfere with the zinc–terpyridine complexes, which link the discrete metallacycles into linear supramolecular polymers, and the conjugation length is extended upon the formation of the zinc–terpyridine complexes, which red-shifts the absorption and emission spectra. Finally, host–guest interactions via bis-ammonium salt binding to the benzo-21-crown-7 (B21C7) groups on the platinum acceptors afford the cross-linked supramolecular polymers. By continuous increase of the concentration of the supramolecular polymer to a relatively high level, supramolecular polymer gel is obtained, which exhibits self-healing properties and reversible gel–sol transitions stimulated by various external stimuli, including temperature, K+, and cyclen. Moreover, the photophysical properties of the supramolecular polymers could be effectively tuned by varying the substituents of the precursor ligands.

The design and synthesis of novel three-dimensional (3-D) supramolecular dendrimers is described. The coordination-driven self-assembly of a 120° diplatinum acceptor and tritopic pyridyl donors bearing [G-0]−[G-3] Fréchet-type dendrons results in a series of supramolecular dendrimers under mild conditions, possessing a robust adamantanoid core of well-defined shape and size. The assemblies were identified using multinuclear (31P and 1H) NMR spectroscopy and electrospray ionization mass spectrometry, as well as pulsed-field-gradient spin−echo (PGSE) NMR measurement together with computational simulations. Isotopically resolved mass spectral data support the existence of the [6 + 4] assembly of adamantanoid dendrimers, and the NMR results are consistent with the formation of these symmetrical assemblies. PGSE NMR measurements together with MMFF force-field modeling clearly reveal the structural feature of the 3-D supramolecular dendrimers with varying sizes.

The syntheses, characterization, and emission properties of three tetragonal prismatic cages, 4a–4c, constructed from eight 90° Pt(II) acceptors, four linear dipyridyl ligands, and two tetraphenylethene (TPE)-based sodium benzoate ligands, are described. These cages are emissive in dilute solutions due to the metal-coordination-induced partial restriction of intramolecular rotation of their TPE units, while the dipyridyl moieties, which act as the pillars as well as the solvents, strongly influence these emissions. Specifically, cages 4aand 4b, bearing a 4,4′-dipyridine and a 1,2-di(4-pyridyl)ethylene as their pillar parts, respectively, display good emissions in common organic solvents at 485–493 nm that are derived from the TPE units. In contrast, cage 4c, with its BODIPY-based dipyridyl unit, exhibits two emission bands at 462–473 and 540–545 nm, originating from the TPE and BODIPY fluorophores, respectively. Moreover, cage 4bhas been employed as a turn-on fluorescent sensor for thiol-containing amino acids via a self-destructive reaction, while the cage can also be regenerated via the addition of Pt(II) acceptors. The studies described herein not only enrich the ongoing research on fluorescent materials but also pave the way to prepare stimuli-responsive supramolecular coordination complexes.

In this work, spectroscopic techniques and quantum chemistry calculations were used to investigate the photophysical properties of various multinuclear platinum complexes with different conformational geometries. This suite of complexes includes a Pt–pyridyl square, a Pt–carboxylate triangle, and a mixed Pt–pyridyl–carboxylate rectangle, as well as two mononuclear Pt model complexes. Studying the individual molecular precursors in the context of larger assemblies is important to provide a complete understanding of the factors governing the observed photophysical properties of a given system. The absorption and emission bands of the parent linear dipyridyl donor (ligand 1) are largely preserved in the [4 + 4] square and the multicomponent [4 + 2 + 2] rectangle (3and 4, respectively), with significant red shifts. The [3 + 3] Pt–carboxylate triangle containing p-phthalic acid is nonemissive. Phosphorescence and nanosecond transient spectroscopy on 3and 4reveal that the introduction of platinum atoms enhances spin–orbital coupling, thereby increasing the rate of intersystem crossing. This phenomenon is consistent with the low fluorescence quantum yields and short fluorescence lifetimes of 3and 4. Moreover, the electronic structures for the ground state and low-lying excited states of these compounds were studied using quantum chemistry calculations. The fluorescent states of the platinum complexes are local excited states of ligand-centered π–π* transition features, whereas the nonfluorescent states are intramolecular charge-transfer states. These low-lying intramolecular charge-transfer states are responsible for the nonemissive nature of small molecules 1and 2and triangle 5. As the interactions between these components determine the properties of their corresponding assemblies, we establish novel excited-state decay mechanisms which dictate the observed spectra.

In this work, the photophysical properties of coordination-driven self-assembled metallosupramolecular rhomboids with the donor ligands 1,2-bis(3-pyridyl)ethyne (3a) and 1,4-bis(3-pyridyl)-1,3-butadiyne (3b) are investigated by use of both spectroscopic experiments and quantum chemistry calculations. All the geometric conformations of the chair and boat conformers of 3aand 3bare fully optimized using density functional theory. The time-dependent density functional theory method was also used to study the excited-state properties of these self-assembled metallosupramolecular rhomboids. At the same time, steady-state absorption and fluorescence as well as the time-correlated single photon counting techniques are used to measure their various spectral properties. The fluorescence spectra of these self-assembled metallosupramolecular rhomboids are very wide and show an evident two-peak feature, which can be tuned by different excitation wavelengths. It has been demonstrated that the chair conformers of both 3aand 3bare formed preferentially over their boat conformers due to the close proximity of the chelated bisphosphine platinum groups. Moreover, an additional shoulder observed at 416 nm in the fluorescence spectra of 3bindicates the presence of minor amounts of the boat conformer of 3b. In addition, we have also demonstrated that lengthening the acetylene chain of the donor ligand component of these rhomboids results in a red-shifted and broadened absorption band for these metallosupramolecular rhomboids. Furthermore, the nature of the excited states for these metallosupramolecular rhomboids varies with the acetylene chain length of the donor ligands and with the different conformers.

Diverse metal–organic complexes (MOCs), shaped as rectangles, triangles, hexagons, prisms, and cages, can be formed by coordination between metal ions (Pt, Pd, Ru, Rh, Ir, Zn, Co, and Cd) and organic ligands, with potential applications as alternatives to conventional biomedical materials for therapeutic, sensing, and imaging purposes. MOCs have been investigated as anticancer drugs in the treatment of malignant tumors in lung, cervical, breast, colon, liver, prostate, ovarian, brain, stomach, bone, skin, mouth, thyroid, and other cancers. MOCs with one, two, and three cavities have also been investigated as drug carriers and prepared for the loading and release of different drugs. In addition, MOCs can target proteins by the shape effect and recognize sugars and DNA by electrostatic interactions, as well as estradiol by host–guest interactions, etc. This Perspective mainly covers achievements in the biomedical application of MOCs. We aim to identify some key trends in the reported MOC structures in relation to their biomedical activity and potential applications.

Two novel discrete organoplatinum(II) metallacycles are prepared by means of coordination-driven self-assembly of a 90° organoplatinum(II) acceptor, cis-(PEt3)2Pt(OTf)2, with two donors, a pyridyl donor, 9,10-di(4-pyridylvinyl)anthracene, and one of two dicarboxylate ligands. Both metallacycles display aggregation-induced emission as well as solvatochromism. More interestingly, both metallacycles exhibit near-infrared fluorescent emission in the solid state and can be used to detect ammonia gas.

In this work, we present the formation of two open-ended hexagonal-prism tubular macrocycles by the [6 + 12] self-assembly of the symmetric ∼120° organic ligand donor with ∼90° Pt(II) acceptor in a 1:2 ratio. The assembled structures were characterized by multinuclear NMR (1H NMR, 31P{1H} NMR, and 1H–1H COSY NMR), electrospray ionization mass spectrometry (ESI-TOF-MS), traveling wave ion mobility–mass spectrometry (TWIM-MS), and transmission electron microscopy. Molecular modeling was further conducted to get insight into their structured characteristics. We also examined their photophysical properties.

Light-harvesting is one of the key steps in photosynthesis, but developing artificial light-harvesting systems (LHSs) with high energy transfer efficiencies has been a challenging task. Here we report fluorescent hexagonal Pt(II) metallacycles as a new platform to fabricate artificial LHSs. The metallacycles (4and 5) are easily accessible by coordination-driven self-assembly of a triphenylamine-based ditopic ligand 1with di-platinum acceptors 2and 3, respectively. They possess good fluorescence properties both in solution and in the solid state. Notably, the metallacycles show aggregation-induced emission enhancement (AIEE) characteristics in a DMSO–H2O solvent system. In the presence of the fluorescent dye Eosin Y (ESY), the emission intensities of the metallacycles decrease but the emission intensity of ESY increases. The absorption spectrum of ESY and the emission spectra of the metallacycles show a considerable overlap, suggesting the possibility of energy transfer from the metallacycles to ESY, with an energy transfer efficiency as high as 65% in the 4a+ESYsystem.

Considerable progress in platinum metallacycle-based supramolecular polymerization has promoted the fabrication and application of supramolecular materials. However, despite recent advances, supramolecular polymers constructed through platinum metallacycle-based host–guest complexation remain rare because of the dynamics of platinum metallacycles. Here, we achieve linear supramolecular polymerization via platinum metallacycle-based host–guest complexation by following the design rule of suppressing the dynamics of the metallacycles. The establishment of the platinum metallacycle-based host–guest system and the realization of this type of supramolecular polymerization are expected to open opportunities for platinum metallacycle-based functional materials.

The intrinsic relationship between the properties of green fluorescent protein (GFP) and its encapsulated small molecular light machine has spurred many biomimicking studies, aiming at revealing the detailed mechanism and further promoting its wide applications in different disciplines. However, how to build a similar confined microenvironment to mimic the cavity of a β-barrel and the fluorescence turn-on process is a fundamental challenge for both chemists and biologists. Herein, two distinct exo- and endo-functionalized tetraphenylethylene (TPE)-based M12L24nanospheres with precise distribution of anchored TPE moieties and unique photophysical properties were constructed by means of a coordination-driven self-assembly strategy. Under dilute conditions, the nanospheres fluoresce more strongly than the corresponding TPE subcomponents. Meanwhile, the endo-functionalized sphere is able to induce a higher local concentration and more restrained motion of the enclosed 24 TPE units compared with exo-functionalized counterpart and thus induces much stronger emission due to the restriction of the rotation of the pendant TPE units. The biomimetic methodology developed here represents a promising way to understand and construct artificial GFP materials on the platforms of supramolecular coordination complexes.

A supramolecular polymeric adhesive was prepared from non-viscous, non-polymeric materials by water–participant hydrogen bonds. Pt–pyridine coordination and water–crown ether hydrogen bonding combine to effect the supramolecular polymerization. The supramolecular polymeric adhesive displays strong, reversible adhesion to hydrophilic surfaces, a property that forecasts the application of hydrogen bonding in advanced supramolecular materials.

A double metallacycle was prepared via the size-selective integrative self-sorting of four different building blocks driven by a reversible metal–ligand coordination interaction. A hydrophobic dendron was placed on a metallacycle and a hydrophilic dendron was attached to the other metallacycle, producing a two-faced Janus-type supramolecule with two distinct functionalities. In aqueous media, hierarchical self-assembly of the supramolecular system was induced by the combination of coordination interactions and hydrophobic–hydrophilic interactions resulting in the formation of micrometer-sized fiber-like structures, a morphology distinct from metallacycles bearing only one type of functionality. This study provides a versatile approach for the construction of Janus-type molecules and demonstrates that integrative self-sorting of a supramolecular coordination system can be utilized for the preparation of complex supramolecular systems with predesigned functionalities and morphologies

The recent progress in platinum(II) coordination-driven supramolecular polymers has had a substantial effect on the design of functional soft materials. However, the prospect of realizing polymerization induced by platinum(II) metallacycle-based host–guest interactions has received little attention until recently. Here we report the realization of supramolecular polymerization driven by platinum(II) metallacycle-based host–guest interactions both in the solid state and in solution. On the basis of the disclosed polymerization mechanism, we present a new strategy for the preparation of platinum(II) metallacycle-based supramolecular polymers.

Supramolecular coordination has been developed as an efficient tool to construct a variety of discrete metallacycles and metallacages with well-defined shapes and sizes. However, its application in framework construction has been barely exploited. In this paper, we report the direct synthesis of two diamondoid frameworks from a simple tetrahedral precursor, tetra(4-(4-pyridinyl)phenyl)methane, and two linear difunctional platinum(II) ligands via one-step supramolecular coordination. Controlled by the specific angularity and geometry of the tetrahedral and linear subunits, these frameworks possess a well-defined diamondoid topology with highly regulated periodicity and three-dimensional porosity. Moreover, these rigid frameworks can be directly changed into a metallogel when prepared in DMSO at high concentrations. Interestingly, these diamondoid frameworks exhibit a cationic nature and stimuli-responsive behavior, which potentially endow them with the selective adsorption and controlled release for anionic dyes and drugs in aqueous environments. Thus, this study demonstrates that supramolecular coordination is a facile and efficient approach for the preparation of functional framework materials containing predesigned and well-defined supramolecular coordination assemblies as molecular skeletons.

A series of platinum(II) metallacycles were prepared via the coordination-driven self-assembly of a phenazine-cored dipyridyl donor with a 90° Pt(II) acceptor and various dicarboxylate donors in a 1:1:2 ratio. While the metallacycles display similar absorption profiles, they exhibit a trend of blue-shifted fluorescence emission with the decrease in the bite angles between the carboxylate building blocks. Comprehensive spectroscopic and dynamic studies as well as a computational approach were conducted, revealing that the difference in the degree of constraint imposed on the excited-state planarization of the phenazine core within these metallacycles results in their distinct photophysical behaviors. As such, a small initial difference in the dicarboxylate building blocks is amplified into distinct photophysical properties of the metallacycles, which is reminiscent of the efficient functional tuning observed in natural systems. In addition to the pre-assembly approach, the photophysical properties of a metallacycle can also be modulated using a post-assembly modification to the dicarboxylate building block, suggesting another strategy for functional tuning. This research illustrated the potential of coordination-driven self-assembly for the preparation of materials with precisely tailored functionalities at the molecular level.

Inspired by assemblies in the natural world, researchers have prepared diverse suprastructures with distinct spatial arrangements by artificial self-assembly, including micelles, vesicles, ribbons, films, fibers, and tubes. The field of assembly is undergoing a transition from single-component to multicomponent assembly and single-step to multistep processing. Control over the size, shape, and composition of these building blocks has enabled the formation of suprastructures with substantial structural diversity. More importantly, harnessing noncovalent interactions to create suprastructures in a controlled manner will lead to a better understanding of the formation of complex self-organized patterns. However, for the construction of multiscale self-assemblies with controllable shapes and functions, the selection of a suitable protocol remains challenging.

The local environment surrounding luminophores can significantly influence their photophysical properties. Herein, we report the self-assembly of a highly emissive platinum(II)-based metallacage. In order to accommodate the connectivity of the platinum(II) building block used in the self-assembly process, the luminophore-containing building block adopts a highly twisted geometry relative to its free form, leading to the emergence of an emissive transition with a radiative rate constant an order of magnitude higher than that of the free luminophore. This increased rate constant is the primary driver for the 10-fold increase in quantum yield from 4.2% to 40%. Model complexes with platinum or methyl groups bound to the nitrogen were synthesized. These complexes had lower quantum yields (10% and non-emissive, respectively) due mainly to decreases in radiative rate constants. Computational studies were conducted and indicated that the excited state of the ensembles, as well as the model complexes, is a result of charge transfer to the pyridyl groups, in contrast to the free luminophore, which involves the diphenyl sulfone moiety. The differences in quantum yields can be explained by a twist in the chromophore upon coordination of platinum or methylation on the pyridyl group, leading to intersystem crossing to a triplet state. This state then becomes more emissive with the addition of platinum, which increases the radiative rate constant via the heavy atom effect. The formation of a metallacage also decreases the non-radiative rate constant by inhibiting the intramolecular motions of the incorporated luminophore.

Constructing polycyclic aromatics-based, highly emissive fluorophores with good solubility and tunable aggregated structures and properties is of great importance for film fabrication, solution processing, and relevant functionality studies. Herein, we describe a general strategy to endow conventional organic fluorophores with enhanced solubility and modulated fluorescent properties via their incorporation into coordination-driven self-assembled metallacycles. A widely used fluorophore, pyrene, was decorated with two pyridyl groups to yield functionalized pyrene 4. Mixing 4with three aromatic dicarboxylates with different lengths and a 90° Pt(II) metal acceptor in a 2:2:4 stoichiometric ratio resulted in the formation of three metallacycles, 1, 2, and 3. The metallacycles display good solubility in polar organic solvents, highly aggregation-dependent fluorescence, and size-dependent emissions at higher concentrations. Moreover, metallacycle 2-based, silica-gel-supported film as fabricated not only is more emissive than the ligand 4-based one but also displays much improved sensing properties for amines in the vapor state, as demonstrated by significantly increased response speed and decreased recovery time. The enhanced solubility, unique fluorescence behavior, and multi-factor modulation character show that coordination-driven self-assembly can be utilized for the development of new fluorophores through simple modification of conventional fluorophores. The fluorophores synthesized this way possess not only complex topological structures but also good modularity and tunability in fluorescence behavior, which are important for grafting multi-stage energy-transfer systems necessary for the development of high-performance sensing materials.

This work provides a platform for the rapid generation of superstructure assemblies with a wide range of lengths that can be used to access a variety of metal–organic complex-based soft superstructures. Metallacage-based microneedles that are nanometers in diameter and millimeters in length were generated in dichloromethane and ethyl acetate; their size could be controlled by adjusting the ratio of the two solvents. Interestingly, microflower structures could be formed by further assembly of the microneedles during solvent evaporation. Our study establishes a feasible method designed to broaden the range of suprastructures with emissions from blue and green to red through the co-assembly of lysine-modified perylene. Similar to the co-assembly of lysine-modified perylene with microflowers, chlorophyll-a and vitamin B12were introduced into the microflowers during the assembly process, which may be exploited in studies of energy capture and nerve repair in the future.

Herein, we present a method for the preparation of supramolecular polymers with tunable fluorescence via the combination of metal–ligand coordination and phenanthrene-21-crown-7 (P21C7)-based host–guest interactions. A suite of rhomboidal metallacycles with different substituents were prepared via the coordination-driven self-assembly of a P21C7-based 60° diplatinum(II) acceptor and 120° dipyridyl donors. Upon variation of the substituents on the dipyridyl donors, the metallacycles exhibit emission wavelengths spanning the visible region (λmax= 427–593 nm). Metallacycle-cored supramolecular polymers were obtained via host–guest interactions between bis-ammonium salts and P21C7. The supramolecular polymers exhibit emission wavelengths similar to those of the individual metallacycles and higher fluorescent efficiency in solution and thin films. Utilizing a yellow-emitting supramolecular polymer thin film with high quantum yield (0.22), a white-light-emitting LED was fabricated by painting the thin film onto an ultraviolet LED. This study presents an efficient approach for tuning the properties of fluorescent supramolecular polymers and the potential of the metallacycle-cored supramolecular polymers as a platform for the fabrication of light-emitting materials with good processability and tunability.

A water-soluble metallosupramolecular hexagon containing pendant methyl viologen (MV) and trimethylammonium units at the vertices has been synthesized via an organoplatinum(II) ← pyridyl coordination-driven self-assembly reaction. The MV units of the metallacycle were further utilized in the formation of a heteroternary complex with cucurbit[8]uril and a galactose-functionalized naphthalene derivative, yielding a metallacycle-cored carbohydrate cluster that was subsequently ordered into nanospheres and tapes, depending upon the concentration.

Cubic metallacages were arranged into multidimensional (one-, two-, and three-dimensional) suprastructures via multistep assembly. Four new shape-controllable, hybrid metallacages with modified substituents and tunable electronic properties were prepared using dicarboxylate ligands with various substituents (sodium sulfonate, nitro, methoxyl, and amine), tetra-(4-pyridylphenyl) ethylene, and cis-(PEt3)2Pt(OTf)2. The as-prepared metallacages were used as building blocks for further assembly. Diverse suprastructures with tunable emissions (λmaxfrom 451 to 519 nm) and various substituents (−SO3Na, −NO2, −OCH3, and −NH2) were prepared depending on the substituents and solvents used.

We report a novel example of supramolecular cages containing a Lewis acidic trigonal boron center. Self-assembly of the tris(pyridyl)borane donor 1with diruthenium (2) or platinum (3), as an electron acceptor, furnished boron-containing trigonal prismatic supramolecular cages 5and 6, which were characterized by 1H NMR and electrospray ionization time-of-flight mass spectroscopy and X-ray crystallography. The molecular structure of cage 5was confirmed as a trigonal prismatic cage with an inner dimension of about 400 Å3. The fluoride binding properties of borane ligand 1and Pt cage 6were studied. UV/vis absorption titration studies demonstrated that the boron center of cage 6undergoes strong binding interaction with the fluoride ion, with an estimated binding constant of 1.3 × 1010M–2in acetone based on the 1:2 binding isotherm. The binding was also confirmed by 1H NMR titration. Photoluminescence titration studies showed that cage 6emitted borane-centered fluorescence (τ = 2.21 ns), which was gradually quenched upon addition of fluoride. When excess fluoride was added to a solution of 6, however, dissociation of the pyridyl ligand from the Pt(II) center was observed.

Hierarchical self-assembly (HAS) is a multilevel organization process that first assembles elementary molecular units into ordered secondary structures via noncovalent interactions, which further act as the building blocks to form more complex multifunctional superstructures at the next level(s). The HAS strategy has been used as a versatile method for the preparation of soft-matter nanoarchitectures of defined size and morphologies, tunable luminescence, and biological importance. However, such preparation can be greatly simplified if well-defined dynamic structures are employed as the cores that upon linking form the desired nanoarchitectures. Discrete supramolecular coordination complexes (SCCs) with well-defined shapes, sizes, and internal cavities have been widely employed to construct hierarchical systems with functional diversity. This Account summarizes the prevailing strategies used in recent years in the preparation of SCC-based HASs and illustrates how the combination of dynamic metal–ligand coordination with other interactions was used to obtain hierarchical systems with interesting properties.

Herein, we report the formation of multinuclear Ir4, Ir6, and Ir12supramolecular complexes via the bridge-driven self-assembly of tetrazolyl ligands. The synthesis of dimeric half-sandwich Ir units was made by the reaction of half-sandwich Ir units and tetrazolyl ligands in a molar ratio of 1:2. The use of different ligands containing multiple tetrazolyl units resulted in the formation of different Ir supramolecular architectures. The reaction of [Cp*IrCl2]2, AgOTf, and 1,2- or 1,3-ditetrazolyl benzene in a molar ratio of 1:3:1 resulted in the formation of rectangular tetranuclear or truncated trigonal pyramidal hexanuclear Ir complexes, respectively. On the other hand, the reaction of [Cp*IrCl2]2, AgOTf, and 1,3,5-tritetrazolyl benzene in a molar ratio of 6:18:4 produced a supramolecular dodecanuclear iridium complex. The molecular structure of the complex resembled a truncated tetrahedral structure with a large inner cavity, as determined by X-ray crystallography.

The synthesis, characterization, and temperature-responsive properties of two fluorescent organoplatinum(II) metallacycles are reported. Metallacycles M1and M2were prepared via the coordination-driven self-assembly of a 120° triarylamine ligand L1and a 120° diplatinum(II) acceptor Pt-1or 180° diplatinum(II) acceptor Pt-2, respectively. M1and M2are hexagonal metallacycles, comprising of three or six freely rotating anthracene pendants on their periphery, respectively. In response to the temperature variation between −20 and 60 °C, the ligand displays irregular emission changes, whereas both metallacycles show reversible absorption and emission spectral changes in THF. The changes in their green emission intensity also exhibit a linear correlation with the temperature variation, with an average sensitivity of −0.67% and −0.77% per °C for M1and M2, respectively. Furthermore, in coordinating solvents, such as DMF and CH3CN, M1and M2show different behaviors: in the lower temperature range, i.e., below 30 °C, their spectral changes are similar to those observed in THF; however, at a higher temperature the metallacycles were presumably destroyed by the solvents and displayed ratiometric fluorescent responses, including a cyan emission of the ligand L1.

Herein, we report the preparation of a multifunctional metallacage-core supramolecular gel by orthogonal metal coordination and host–guest interactions. A tetragonal prismatic cage with four appended 21-crown-7 (21C7) moieties in its pillar parts was first prepared via the metal-coordination-driven self-assembly of cis-Pt(PEt3)2(OTf)2, tetraphenylethene (TPE)-based sodium benzoate ligands and linear dipyridyl ligands. Further addition of a bisammonium linker to the cage delivered a supramolecular polymer network via the host–guest interactions between the 21C7 moieties and ammonium salts, which formed a supramolecular gel at relatively higher concentrations. Due to the incorporation of a TPE derivative as the fluorophore, the gel shows emission properties. Multiple stimuli responsiveness and good self-healing properties were also observed because of the dynamic metal coordination and host–guest interactions used to stabilize the whole network structure. Moreover, the storage and loss moduli of the gel are 10-fold those of the gel without the metallacage cores, indicating that the rigid metallacage plays a significant role in enhancing the stiffness of the gel. The studies described herein not only enrich the functionalization of fluorescent metallacages via elegant ligand design but also provide a way to prepare stimuli-responsive and self-healing supramolecular gels as robust and smart materials.

Herein, we report the synthesis of two novel ionic Ti complexes possessing three [N,O]-type bidentate ligands from the reaction of Fe metallascorpionate ligands possessing extended alcohol groups and TiCl4. The reaction of substituted hydroxyphenyl tetrazole and Fe(ClO4)3in a molar ratio of 3:1 afforded iron scorpionate metalloligands possessing extended arms, which were characterized by IR spectroscopy and ESI-TOF-MS spectrometry. Their molecular structures were also confirmed as neutral Fe-centered scorpionate complexes by X-ray crystallography, in which the extended alcohol groups adopted a tripodal geometry. Moreover, two different crystals of iron scorpionate metalloligand grown from CH2Cl2and CH3OH were studied, revealing that, in the latter crystal, the tripod arms are folded and aligned toward the C3-rotational axis of the molecule, whereas the tripod arms are unfolded and spread outward from the rotational axis in the former crystal. These metalloligands are solvatochromatic; a bathochromic shift was observed as the solvent polarity increased. From the reaction, the aforesaid Fe complexes were further reacted with TiCl4in a molar ratio of 1:1 to produce ionic [TiL3]+[FeCl4]−(L= substituted hydroxyphenyl tetrazole) complexes from the transmetalation of Ti and Fe. The complexes were characterized by various analytical methods including UV/vis and IR spectroscopies, electrospray time-of-flight mass spectrometry (ESI-TOF-MS), and X-ray crystallography.