Aqueous Platinum(II)-Cage-Based Light-Harvesting System for Photocatalytic Cross-Coupling Hydrogen Evolution Reaction

Self-Assembly of a Water-Soluble Pd16 Square Bicupola Architecture and Its Use in Aerobic Oxidation in Aqueous Medium

Designing supramolecular architectures with uncommon geometries has always been a key goal in the field of metal-ligand coordination-driven self-assembly. It acquires added significance if functional building units are employed in constructing such architectures for fruitful applications. In this report, we address both these aspects by developing a water-soluble Pd16L8 coordination cage 1 with an unusual square orthobicupola geometry, which was used for selective aerobic oxidation of aryl sulfides. Self-assembly of a benzothiadiazole-based tetra-pyridyl donor L with a ditopic cis-[(tmeda)Pd(NO3)2] acceptor [tmeda = N,N,N',N'-tetramethylethane-1,2-diamine] produced 1, and the geometry was determined by single-crystal X-ray diffraction study. Unlike the typically observed tri- or tetrafacial barrel, the present Pd16L8 coordination assembly features a distinctive structural topology and is a unique example of a water-soluble molecular architecture with a square orthobicupola geometry. Efficient and selective aerobic oxidation of sulfides to sulfoxides is an important challenge as conventional oxidation generally leads to the formation of sulfoxide along with toxic sulfone. Cage 1, designed with a ligand containing a benzothiadiazole moiety, demonstrates an ability to photogenerate reactive oxygen species (ROS) in water, thus enabling it to serve as a potential photocatalyst. The cage showed excellent catalytic efficiency for highly selective conversion of alkyl and aryl sulfides to their corresponding sulfoxides, therefore without the formation of toxic sulfones and other byproducts, under visible light in aqueous medium.

Supramolecular Sequential Light-Harvesting Systems for Constructing White LED Device and Latent Fingerprint Imaging

The fabrication of supramolecular light-harvesting systems (LHS) with sequential energy transfer is of significance in utilizing light energy. In this study, we report the non-covalent self-assembly of a sequential LHS by pillar[5]arene-based host-guest interaction in water and its applications in white light-emitting diode (LED) device and latent fingerprint imaging. The host-guest complex WP5 ⊃ ${ \supset }$ G self-assembles into nanoparticles in water and shows enhanced aggregation-induced emission (AIE) effect. The nanoparticles can be further used to construct sequential LHS with fluorescent dyes 4,7-di(2-thienyl)-benzo[2,1,3]thiadiazole (DBT) and sulforhodamine 101 (SR101). Impressively, the system shows white-light emission when the molar ratio of WP5 ⊃ ${ \supset }$ G/DBT/SR101 is 1100/2/16. The material can be coated on a LED bulb to achieve white-light emission. In addition, the sequential LHS exhibit multicolor fluorescence including red emission, which have been successfully applied to high-resolution imaging of latent fingerprints. Therefore, we demonstrated a general strategy for the construction of sequential LHS in water based on macrocyclic host-guest interaction and explored its multi-functional applications in white-light LED device and imaging of latent fingerprints, which will promote future development and application of supramolecular LHSs.

Pt(II)/Pd(II)-Based Metallosupramolecular Architectures as Light Harvesting Systems and their Applications

The development of artificial light-harvesting systems mimicking the natural photosynthesis method is an ever-growing field of research. Numerous systems such as polymers, metal complexes, POFs, COFs, supramolecular frameworks etc. have been fabricated to accomplish more efficient energy transfer and storage. Among them, the supramolecular coordination complexes (SCCs) formed by non-covalent metal-ligand interaction, have shown the capacity to not only undergo single and multistep energy migration but also to utilize the harvested energy for a wide variety of applications such as photocatalysis, tunable emissive systems, encrypted anti-counterfeiting materials, white light emitters etc. This review sheds light on the light-harvesting behavior of both the 2D metallacycles and 3D metallacages where design ingenuity has been executed to afford energy harvesting by both donor ligands as well as metal acceptors.

Multi-step FRET systems based on discrete supramolecular assemblies

Fluorescence resonance energy transfer (FRET) from the excited state of the donor to the ground state of the acceptor is one of the most important fluorescence mechanisms and has wide applications in light-harvesting systems, light-mediated therapy, bioimaging, optoelectronic devices, and information security fields. The phenomenon of sequential energy transfer in natural photosynthetic systems provides great inspiration for scientists to make full use of light energy. In recent years, discrete supramolecular assemblies (DSAs) have been successively constructed to incorporate donor and multiple acceptors, and to achieve multi-step FRET between them. This perspective describes recent advances in the fabrication and application of DSAs with multi-step FRET. These DSAs are categorized based on the non-covalent scaffolds, such as amphiphilic nanoparticles, host-guest assemblies, metal-coordination scaffolds, and biomolecular scaffolds. This perspective will also outline opportunities and future challenges in this research area.

Guest-Regulated Generation of Reactive Oxygen Species from Porphyrin-Based Multicomponent Metallacages for Selective Photocatalysis

The development of novel materials for highly efficient and selective photocatalysis is crucial for their practical applications. Herein, we employ the host-guest chemistry of porphyrin-based metallacages to regulate the generation of reactive oxygen species and further use them for the selective photocatalytic oxidation of benzyl alcohols. Upon irradiation, the sole metallacage (6) can generate singlet oxygen (1O2) effectively via excited energy transfer, while its complex with C70 (6⊃C70) opens a pathway for electron transfer to promote the formation of superoxide anion (O2⋅-), producing both 1O2 and O2⋅-. The addition of 4,4'-bipyridine (BPY) to complex 6⊃C70 forms a more stable complex (6⊃BPY) via the coordination of the Zn-porphyrin faces of 6 and BPY, which drives fullerenes out of the cavities and restores the ability of 1O2 generation. Therefore, benzyl alcohols are oxidized into benzyl aldehydes upon irradiation in the presence of 6 or 6⊃BPY, while they are oxidized into benzoic acids when 6⊃C70 is employed as the photosensitizing agent. This study demonstrates a highly efficient strategy that utilizes the host-guest chemistry of metallacages to regulate the generation of reactive oxygen species for selective photooxidation reactions, which could promote the utilization of metallacages and their related host-guest complexes for photocatalytic applications.

Modifying the Oxidative Potentials of Imines in a Dye Loaded Capsule for Photocatalytic Cyclization with Hydrogen Evolution

Modifying redox potential of substrates and intermediates to balance pairs of redox steps are important stages for multistep photosynthesis but faced marked challenges. Through co-clathration of iridium photosensitizer and imine substrate within one packet of a metal-organic capsule to shift the redox potentials of substrate, herein, we reported a multiphoton enzymatic strategy for the generation of heterocycles by intramolecular C-X hydrogen evolution cross-couplings. The cage facilitated a pre-equilibrium substrate-involving clathrate that cathodic shifts the oxidation potential of the substrate-dye-host ternary complex and configuration inversion of substrate via spatial constraints in the confined space. The new two photon excitation strategy enabled the precise control of the multistep electron transfer between each pair (photosensitizer, substrate and the capsule), endowing the catalytic system proceeding smoothly with an enzymatic fashion. Three kinds of 2-subsituted (-OH, -NH2 , and -SH) imines and N-aryl enamines all give the corresponding cyclization products efficiently under visible light irradiation, demonstrating the promising of the microenvironment driven thermodynamic activation in the host-dye-substrate ternary for synergistic combination of multistep photocatalytic transformations.

A water-soluble Pd4 molecular tweezer for selective encapsulation of isomeric quinones and their recyclable extraction

Quinones (QN) are one of the main components of diesel exhaust particulates that have significant detrimental effects on human health. Their extraction and purification have been challenging tasks because these atmospheric particulates exist as complex matrices consisting of inorganic and organic compounds. In this report, we introduce a new water soluble Pd4L2 molecular architecture (MT) with an unusual tweezer-shaped structure obtained by self-assembly of a newly designed phenothiazine-based tetra-imidazole donor (L) with the acceptor cis-[(tmeda)Pd(NO3)2] (M) [ tmeda = N,N,N',N'-tetramethylethane-1,2-diamine]. The molecular tweezer encapsulates some quinones existing in diesel exhaust particulates (DEPs) leading to the formation of host-guest complexes in 1 : 1 molar ratio. Moreover, MT binds phenanthrenequinone (PQ) more strongly than its isomer anthraquinone (AQ), an aspect that enables extraction of PQ with a purity of 91% from an equimolar mixture of the two isomers. Therefore, MT represents an excellent example of supramolecular receptor capable of selective aqueous extraction of PQ from PQ/AQ with many cycles of reusability.

Construction of an Artificial Light-Harvesting System with Photocatalytic Activity Based on Nor-seco-cucurbit[10]uril in Aqueous Solution

A supramolecular assembly was constructed based on the tetraphenylethylene derivatives (TPEs) and nor-seco-cucurbit[10]uril (ns-Q[10]). Upon introduction of the dye Rhodamine B (RB) into the TPEs@ns-Q[10] assembly, an energy transfer process can occur from the TPEs@ns-Q[10] assembly to RB. Moreover, after the addition of Nile Red (NiR), a two-step sequential energy transfer process from the TPEs@ns-Q[10] assembly to RB and then to NiR can occur. Additionally, the dye Eosin Y (ESY) was introduced into the TPEs@ns-Q[10] assembly and an energy transfer process can take place from the TPEs@ns-Q[10] assembly to ESY. To utilize the harvested energy from the TPEs@ns-Q[10]-RB-NiR and TPEs@ns-Q[10]-ESY system, we applied the TPEs@ns-Q[10] assembly-based light-harvesting systems (LHSs) as a catalyst for the advancement of the photocatalytic dehalogenation reaction in aqueous solution. When promoted with 0.5 mol % catalyst, the reaction yield reached 78 and 68%, demonstrating the promising potential of TPEs@ns-Q[10] assembly-based LHSs in the promotion of the photocatalytic dehalogenation reaction.

Carbazole-based artificial light-harvesting system for photocatalytic cross-coupling dehydrogenation reaction

A carbazole-based artificial light-harvesting system (LHS) was successfully fabricated based on the supramolecular assembly of AIE-enhanced donor (CTD), water-soluble phosphate-pillar[5]arene (WPP5), and eosin Y (ESY) acceptor. The formed WPP5-CTD possessed remarkable AIE emission, featuring an ideal energy donor for light harvesting. After encapsulation of ESY, the energy of WPP5-CTD was efficiently transferred to ESY in WPP5-CTD-ESY, and the antenna effect was 38.5, which was much higher than that of recently reported LHSs. Notably, WPP5-CTD-ESY was successfully utilized as a photocatalyst to realize the cross-coupling dehydrogenation reaction of diphenylphosphine oxide and benzothiazole derivatives, suggesting great potential for aqueous photocatalytic applications of this LHS.

Pt(II) Tetrafacial Barrel with Aggregation-Induced Emission for Sensing

A new tetraphenylpyrazine-based tetraimidazole ligand (L) was synthesized and used for subcomponent self-assembly with cis-(tmeda)Pd(NO3)2 and cis-Pt(PEt3)2(OTf)2, leading to the formation of two tetrafacial barrels [Pd8L4(tmeda)8](NO3)16 (1) and [Pt8L4(PEt3)16](OTf)16 (2), respectively. Although ligand L is aggregation-induced emission (AIE) active, barrel 2 showed a magnificently higher AIE activity than ligand L, while 1 failed to retain the AIE properties of the ligand. Pd(II) barrel 1, undergoing an aggregation-caused quenching (ACQ) phenomenon, nullified the AIE activity of the ligand to be used in the photophysical application. The enhanced emission in the aggregated state of Pt(II) barrel 2 was used for the recognition of picric acid (PA), which is explosive in nature and one of the groundwater contaminants in landmine areas. The recognition of picric acid was found to be selective in comparison with that of other nitroaromatic compounds (NACs), which could be attributed to ground-state complex formation and resonance energy transfer between picric acid and barrel 2. The use of new AIE-active assembly 2 for selective detection of PA with a low detection limit is noteworthy.

Self-Assembly of an [M8 L24 ]16+ Intertwined Cube and a Giant [M12 L16 ]24+ Orthobicupola

Through coordination-driven self-assembly, aesthetically captivating structures can be formed by tuning the length or flexibility of various components. The self-assembly of an elongated rigid terphenyl-based tetra-pyridyl ligand (L1) with a cis-Pd(II) acceptor produces an [M12 L16 ]24+ triangular orthobicupola structure (1). When flexibility is introduced into the ligand by the incorporation of a -CH2 - group between the dipyridylamine and terphenyl rings in the ligand (L2), anunique [M8 L24 ]16+ water-soluble 'intertwined cubic structure' (2) results. The inherent flexibility of ligand L2 might be the key factor behind the formation of the thermodynamically stable and 'intertwined cubic structure' in this scenario. This research showcases the ability to design and fabricate novel, topologically distinctive molecular structures by a straightforward and efficient approach.

Cavity-Shape-Dependent Divergent Chemical Reaction inside Aqueous Pd6L4 Cages

Chemical reactions inside the confined pockets of enzyme-mimicking hosts, such as cages and macrocycles, have been an emerging field of interest over the past decade. Although many such reactions are known, the use of such cages toward the divergent synthesis of nonisomeric products has not been well explored. Divergent synthesis is a technique of forming two or more distinct products from the same reagents by changing the catalyst or reaction conditions. Changing the shape of the cage can also change the nature and magnitude of the host-guest interactions. Thus, is it possible for such changes to cause differences in the reaction pathways leading to formation of nonisomeric products? Herein, we report a divergent chemical transformation of anthrone [anthracen-9(10H)-one] inside different water-soluble M6L4 cages. When anthrone was encapsulated inside a newly synthesized M6L4 octahedral cage 1, it dimerized to form dianthrone [9,9'-bianthracen-10,10'(9H,9'H)-dione]. In contrast, when the same chemical reaction was performed inside a M6L4 double-square shaped cage 2, it was oxidized to form anthraquinone [anthracene-9,10-dione]. Similar results were obtained with a different set of isomeric aqueous Pd6 cages 3a (octahedral cage) and 3b (double-square cage), indicating the dependence of the shape of cavity on the divergent synthesis. The present report demonstrates a unique example of different outcomes/results of a reaction depending on the shape of the molecular container, which was driven by the host-guest interactions and the preorganization of the substrates.

Applications of Supramolecular Polymers Generated from Pillar[n]arene-Based Molecules

Supramolecular chemistry enables the manipulation of functional components on a molecular scale, facilitating a "bottom-up" approach to govern the sizes and structures of supramolecular materials. Using dynamic non-covalent interactions, supramolecular polymers can create materials with reversible and degradable characteristics and the abilities to self-heal and respond to external stimuli. Pillar[n]arene represents a novel class of macrocyclic hosts, emerging after cyclodextrins, crown ethers, calixarenes, and cucurbiturils. Its significance lies in its distinctive structure, comparing an electron-rich cavity and two finely adjustable rims, which has sparked considerable interest. Furthermore, the straightforward synthesis, uncomplicated functionalization, and remarkable properties of pillar[n]arene based on supramolecular interactions make it an excellent candidate for material construction, particularly in generating interpenetrating supramolecular polymers. Polymers resulting from supramolecular interactions involving pillar[n]arene find potential in various applications, including fluorescence sensors, substance adsorption and separation, catalysis, light-harvesting systems, artificial nanochannels, and drug delivery. In this context, we provide an overview of these recent frontier research fields in the use of pillar[n]arene-based supramolecular polymers, which serves as a source of inspiration for the creation of innovative functional polymer materials derived from pillar[n]arene derivatives.

A cavitand-based supramolecular artificial light-harvesting system with sequential energy transfer for photocatalysis

A novel artificial light-harvesting system, featuring sequential energy transfer processes, has been successfully constructed, which demonstrated white light emission through a precise adjustment of the donor-acceptor ratio. To better mimic natural photosynthesis, the system is employed as a nanoreactor for the photocatalysis of a cross-dehydrogenative coupling (CDC) reaction in aqueous solution.

Construction of an efficient artificial light-harvesting system based on hyperbranched polyethyleneimine and improvement of photocatalytic performance

An artificial light-harvesting system (ALHS) was developed in aqueous solution by employing the electrostatic co-assembly of a tetraphenylethylene derivative modified with two sulfonate groups (TPE-BSBO) and hyperbranched polyethyleneimine (PEI) as the energy donors, and 4,7-bis(2-thienyl)-2,1,3-benzothiadiazole (DBT) as the energy acceptors. The ALHS exhibits not only high efficiency in energy transfer and conversion but also a significant enhancement in the generation of reactive oxygen species (ROS), especially superoxide anion radicals (O2˙-), facilitating its utilization in photocatalytic oxidation reactions.

A supramolecular artificial light-harvesting system based on a luminescent platinum(II) metallacage

A trigonal luminescent metallacage was constructed by the coordination-driven self-assembly of m-pyridine-modified tetraphenylene ligands with organic Pt(II) acceptors, which exhibited excellent Aggregation-Induced Emission (AIE) properties. An efficient artificial light-harvesting system was successfully constructed by selecting the metallacage as the donor and the hydrophobic fluorescent dye Nile Red (NiR) as the donor molecule in a system of acetone/water (1/9, v/v), The absorption spectra of NiR and the emission spectra of the metallacage showed considerable overlap, achieving energy transfer from the metallacage to NiR.

Excited-Multimer Mediated Supramolecular Upconversion on Multicomponent Lanthanide-Organic Assemblies

Upconversion (UC) is a fascinating anti-Stokes-like optical process with promising applications in diverse fields. However, known UC mechanisms are mainly based on direct energy transfer between metal ions, which constrains the designability and tunability of the structures and properties. Here, we synthesize two types of Ln8L12-type (Ln for lanthanide ion; L for organic ligand L1 or L2R/S) lanthanide-organic complexes with assembly induced excited-multimer states. The Yb8(L2R/S)12 assembly exhibits upconverted multimer green fluorescence under 980 nm excitation through a cooperative sensitization process. Furthermore, upconverted red emission from Eu3+ on the heterometallic (Yb/Eu)8L12 assemblies is also realized via excited-multimer mediated energy relay. Our findings demonstrate a new strategy for designing UC materials, which is crucial for exploiting photofunctions of multicomponent lanthanide-organic complexes.

A Two-Step Fluorescence-Resonance Energy Transfer System Constructed by Platinum(II) Metallacycle Based Molecular Recognition

Considerable progress in the construction of efficient fluorescence-resonance energy transfer (FRET) systems has promoted the development of artificial energy transfer materials. However, despite recent advances, the exploration of efficient and easy strategies to fabricate novel supramolecular systems with FRET activities is still a challenge. Here, we report that a two-step FRET system was successfully achieved, driven by platinum metallacycle based host-guest interactions. The two-step FRET system is used for the preparation of a white-light-emitting diode and serves as a nanoreactor for the photosynthetic process. This work offers a strategy for the fabrication of FRET systems and opens opportunities for functional materials constructed by platinum(II) metallacycle based host-guest interactions.

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.

An artificial light-harvesting system constructed from a water-soluble metal-organic barrel for photocatalytic aerobic reactions in aqueous media

An artificial light-harvesting system constructed from a water-soluble host-guest complex can be regarded as a high-level conceptual model of its biological counterpart and can convert solar energy into chemical energy in an aqueous environment. Herein, a water-soluble metal-organic barrel Ga-tpe with twelve sulfonic acid units was obtained by subcomponent self-assembly between Ga3+ ions and tetra-topic ligands with tetraphenylethylene (TPE) cores. By taking advantage of host-guest interactions, cationic dye rhodamine B (RB) was constrained in the pocket of Ga-tpe to promote the Förster resonance energy transfer (FRET) process for efficient photocatalytic aerobic oxidation of sulfides and cross-dehydrogenative coupling (CDC) reaction in aqueous media.

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

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

Near-Infrared Emissive Cascaded Artificial Light-Harvesting System with Enhanced Antibacterial Efficiency

Combination of platinum(II) metallacycles and photodynamic inactivation presents a promising antibacterial strategy. Herein, a cascaded artificial light-capturing system is developed in which an aggregation-induced emission-active platinum(II) metallacycle (PtTPEM) is utilized as the antenna, sulforhodamine 101 (SR101) as a key conveyor, and the near-infrared emissive photosensitizer Chlorin-e6 (Ce6) as the final energy acceptor. The well-dispersed Ce6 in the proximity of energy donors not only avoids self-quenching in the physiological environment but also contributes to energy transfer from donor to acceptor, thereby significantly improving the 1 O2 generation ability of the light-harvesting system under white light irradiation. By integrating the platinum(II) metallacycle and 1 O2 , a more efficient synergistic antibacterial effect is achieved at low concentrations, along with a significant decrease in dark toxicity caused by PtTPEM.

Synthesis of an Adaptable Molecular Barrel and Guest Mediated Stabilization of Its Metastable Higher Homologue

Structural and functional modulation of three-dimensional artificial macromolecular systems is of immense importance. Designing supramolecular cages that can show stimuli mediated reversible switching between higher-order structures is quite challenging. We report here construction of a Pd₆ trifacial barrel (1) by coordination self-assembly. Surprisingly, barrel 1 was found to exhibit guest-responsive behavior. In presence of fullerenes C₆₀ and C₇₀, 1 unprecedentedly transformed to its metastable higher homologue Pd₈ tetrafacial barrel (2), forming stable host-guest complexes (C₆₀)₃⊂2 and (C₇₀)₂⊂2, respectively. Again, encapsulated fullerenes could be extracted from the cavity of 2 using 1,2-dichlorobenzene, leading to its facile conversion to the parent trifacial barrel 1. Such reversible structural interconversion between an adaptable molecular barrel and its guest stabilized higher homologue is an uncommon observation.

Rigidification-Induced Emissive Metal-Carbene Complexes for Artificial Light Harvesting

A tetraphenylethylene (TPE)-based flexible imidazolium (L) salt was used to develop a di-nuclear silver(I)-tetracarbene (1) complex. Coordination-induced rigidity upon formation of 1 exhibited a 6-fold increase in emission intensity in acetonitrile compared to starting L. Despite TPE being a well-known aggregation-induced emissive moiety, Ag^I-N-heterocyclic carbene (NHC) complex 1 had a remarkably higher fluorescence emission (4-fold) in dilute solution when compared with L in its aggregated state. Finally, this enhanced emission was used to institute a new platform for an artificial light-harvesting system. 1 acted as an energy donor and efficiently transferred energy to Eosin Y (ESY) with a high saturation at a 67:1 (1/ESY) molar ratio. Use of rigidification-induced emission of the Ag^I-NHC complex to fabricate a light-harvesting scaffold is a new approach and can greatly impact the generation of smart materials.

Water-soluble phosphate-pillar[5]arene (WPP5)-based artificial light-harvesting system for photocatalytic cross-coupling dehydrogenation

A novel water-soluble phosphate-pillar[5]arene (WPP5)-based artificial light-harvesting system (LHS) was successfully fabricated through the supramolecular assembly of phenyl-pyridyl-acrylonitrile derivative (PBT), WPP5, and organic pigment Eosin Y (ESY). Initially, after host-guest interaction, WPP5 could bind well with PBT and form WPP5 ⊃ PBT complexes in water, which further assembled into WPP5 ⊃ PBT nanoparticles. WPP5 ⊃ PBT nanoparticles performed an outstanding aggregation-induced emission (AIE) capability because of the J-aggregates of PBT in WPP5 ⊃ PBT nanoparticles, which were appropriate as fluorescence resonance energy transfer (FRET) donors for artificial light-harvesting. Moreover, due to the emission region of WPP5 ⊃ PBT overlapped well with the UV-Vis absorption of ESY, the energy of WPP5 ⊃ PBT (donor) could be significantly transferred to ESY (acceptor) via FRET process in WPP5 ⊃ PBT-ESY nanoparticles. Notably, the antenna effect (AE_{WPP5⊃PBT-ESY}) of WPP5 ⊃ PBT-ESY LHS was determined to be 30.3, which was much higher than that of recent artificial LHSs for photocatalytic cross-coupling dehydrogenation (CCD) reactions, suggesting a potential application in photocatalytic reaction. Furthermore, through the energy transfer from PBT to ESY, the absolute fluorescence quantum yields performed a remarkable increase from 14.4% (for WPP5 ⊃ PBT) to 35.7% (for WPP5 ⊃ PBT-ESY), further confirming their FRET processes in WPP5 ⊃ PBT-ESY LHS. Subsequently, in order to output the harvested energy for catalytic reactions, WPP5 ⊃ PBT-ESY LHSs were used as photosensitizers to catalyze the CCD reaction of benzothiazole and diphenylphosphine oxide. Compared to free ESY group (21%), a significant cross-coupling yield of 75% in WPP5 ⊃ PBT-ESY LHS was observed, because more UV region energy of PBT was transferred to ESY for CCD reaction, which suggested more potential in improving the catalytic activity of organic pigment photosensitizers in aqueous systems.

[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.

Self-assembled supramolecular artificial light-harvesting nanosystems: construction, modulation, and applications

Artificial light-harvesting systems, an elegant way to capture, transfer and utilize solar energy, have attracted great attention in recent years. As the primary step of natural photosynthesis, the principle of light-harvesting systems has been intensively investigated, which is further employed for artificial construction of such systems. Supramolecular self-assembly is one of the feasible methods for building artificial light-harvesting systems, which also offers an advantageous pathway for improving light-harvesting efficiency. Many artificial light-harvesting systems based on supramolecular self-assembly have been successfully constructed at the nanoscale with extremely high donor/acceptor ratios, energy transfer efficiency and the antenna effect, which manifests that self-assembled supramolecular nanosystems are indeed a viable way for constructing efficient light-harvesting systems. Non-covalent interactions of supramolecular self-assembly provide diverse approaches to improve the efficiency of artificial light-harvesting systems. In this review, we summarize the recent advances in artificial light-harvesting systems based on self-assembled supramolecular nanosystems. The construction, modulation, and applications of self-assembled supramolecular light-harvesting systems are presented, and the corresponding mechanisms, research prospects and challenges are also briefly highlighted and discussed.

Construction of artificial light-harvesting systems based on a variety of polyelectrolyte materials and application in photocatalysis

In the present work, we designed and synthesized a cationic cyano-substituted p-phenylenevinylene derivative (PPTA), which can form supramolecular assemblies through electrostatic interaction with a type of polyelectrolyte material anionic guar gum (GP5A). A polyelectrolyte-based artificial light-harvesting system (LHS) was constructed by selecting a fluorescent dye sulforhodamine 101 (SR101) that matched its energy level as an energy acceptor. The energy harvested by the acceptors was used in the aqueous phase cross dehydrogenation coupling (CDC) reaction with a yield of up to 87%. In addition, the general applicability of polyelectrolyte materials to build artificial LHS was demonstrated by three other polyelectrolyte materials sodium polyphenylene sulfonate (RSS), sodium carboxymethyl cellulose (CMC), and sodium polyacrylate (PAAS), in which the CDC reaction was also carried out by these three LHSs and obtained high yields. This work not only provides a new method to construct LHSs by using polyelectrolyte materials, but also provides a beneficial exploration for further applying the energy harvested in LHSs to the field of photocatalysis in an aqueous solution.

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.

Water-Soluble Metallo-Supramolecular Nanoreactors for Mediating Visible-Light-Promoted Cross-Dehydrogenative Coupling Reactions

Water-soluble metallo-supramolecular cages with well-defined nanosized cavities have a wide range of functions and applications. Herein, we design and synthesize two series of metallo-supramolecular octahedral cages based on the self-assembly of two congeneric truxene-derived tripyridyl ligands modified with two polyethylene glycol (PEG) chains, i.e., monodispersed tetraethylene glycol (TEG) and polydispersed PEG-1000, with four divalent transition metals (i.e., Pd, Cu, Ni, and Zn). The resulting monodispersed cages C1-C4 are fully characterized by electrospray ionization mass spectrometry (ESI-MS), nuclear magnetic resonance (NMR) spectroscopy, and single-crystal X-ray diffraction. The polydispersed cages C5-C8 display good water solubilities and can act as nanoreactors to mediate visible-light-promoted C(sp³)-C(sp²) cross-dehydrogenative coupling reactions in an aqueous phase. In particular, the most robust Pd(II)-linked water-soluble polydispersed nanoreactor C5 is characterized by ESI-MS and capable of mediating the reactions with the highest efficiencies. Detailed host-guest binding studies in conjunction with control studies suggest that these cages could encapsulate the substrates simultaneously inside its hydrophobic cavity while interacting with the photosensitizer (i.e., eosin Y).

Highly efficient Förster resonance energy transfer between an emissive tetraphenylethylene-based metal-organic cage and the encapsulated dye guest

The host-guest strategy presents an ideal way to achieve efficient Förster resonance energy transfer (FRET) by forcing close proximity between an energy donor and acceptor. Herein, by encapsulating the negatively charged acceptor dyes eosin Y (EY) or sulforhodamine 101 (SR101) in the cationic tetraphenylethene-based emissive cage-like host donor Zn-1, host-guest complexes were formed that exhibit highly efficient FRET. The energy transfer efficiency of Zn-1⊃EY reached 82.4%. To better verify the occurrence of the FRET process and make full use of the harvested energy, Zn-1⊃EY was successfully used as a photochemical catalyst for the dehalogenation of α-bromoacetophenone. Furthermore, the emission color of the host-guest system Zn-1⊃SR101 could be adjusted to exhibit bright white-light emission with the CIE coordinates (0.32, 0.33). This work details a promising approach to enhance the efficiency of the FRET process by the creation of a host-guest system between the cage-like host and dye acceptor, thus serving as a versatile platform for mimicking natural light-harvesting systems.

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.

A Platinum(II)-Based Molecular Cage with Aggregation-Induced Emission for Enzymatic Photocyclization of Alkynylaniline

Enzymes facilitate chemical conversions through the collective activity of aggregated components, but the marriage of aggregation-induced emission (AIE) with molecular containers to emulate enzymatic conversion remains challenging. Herein, we report a new approach to construct a Pt^II -based octahedral cage with AIE characteristics for the photocyclization of alkynylaniline by restricting the rotation of the pendant phenyl rings peripheral to the Pt^II corner. With the presence of water, the C-H⋅⋅⋅π interactions involving the triphenylphosphine fragments resulted in aggregation of the molecular cages into spherical particles and significantly enhanced the Pt^II -based luminescence. The kinetically inert Pt-NP chelator, with highly differentiated redox potentials in the ground and excited states, and the efficient coordination activation of the platinum corner facilitated excellent catalysis of the photocyclization of alkynylaniline. The enzymatic kinetics and the advantages of binding and activating substrates in an aqueous medium provide a new avenue to develop mimics for efficient photosynthesis.

Artificial supramolecular light-harvesting systems based on a pyrene derivative for photochemical catalysis

A supramolecular polymer based on NPyP and CB[8] was constructed via host–guest interactions with the AIE effect for artificial light-harvesting energy transfer and photocatalysis.

Aggregation-Induced Emission Metallocuboctahedra for White Light Devices

Materials for organic light-emitting devices which exhibit superior emission properties in both the solution and solid states with a high fluorescence quantum yield have been extensively sought after. Herein, two metallocages, S1 and S2, were constructed, and both showed typical aggregation-induced emission (AIE) features with intense yellow fluorescence. By adding blue-emissive 9,10-dimethylanthracene, pure white light emission can be produced in the solution of S1 and S2. Furthermore, due to the remarkable AIE feature and good fluorescence quantum yield in the solid state, metallocages are highly emissive in the solid state and can be utilized to coat blue LED bulbs or integrate with blue-emitting chips to obtain white light. This study advances the usage of metallocages as practical solid-state fluorescent materials and provides a fresh perspective on highly emissive AIE materials.

Non-Covalent Dimer as Donor Chromophore for Constructing Artificial Light-Harvesting System in Water

Dynamic emissive materials in aqueous media have received much attention owing to their ease of preparation, tunable luminescence and environmental friendliness. However, hydrophobic fluorophores usually suffer from aggregation-caused quenching in water. In this work, we constructed an artificial light-harvesting system by using a non-covalent aggregation-induced emission dimer as antenna and energy donor. The dimer is quadruple hydrogen bonded from a ureidopyrimidinone derivative (M) containing a tetraphenylethylene group. The dispersed nano-assemblies based on the dimer in aqueous media were fabricated with the help of surfactant. By loading a hydrophobic acceptor molecule DBT into the nano-assemblies, man-made light-harvesting nanoparticles were fabricated, showing considerable energy transfer efficiency and a relatively high antenna effect. Additionally, the fluorescence color of the system can be gradually tuned by varying the content of the acceptors. This study provides a general way for the construction of an aqueous light-harvesting system based on a supramolecular dimer, which is important for potential application in luminescent materials.

Supramolecular polymers based on host-guest interactions for the construction of artificial light-harvesting systems

In the present work, artificial light-harvesting systems with a fluorescence resonance energy transfer (FRET) process were successfully obtained in the aqueous solution. We designed and synthesized an amphiphilic pyrene derivative with two 4-vinylpyridium arms (Pmvb), which can interact with cucurbit[8]uril (CB[8]) to form supramolecular polymer through host-guest interactions in aqueous solution. The formation of supramolecular polymers results in a significant enhancement of fluorescence, which makes Pmvb-CB[8] an ideal energy donor to construct artificial light-harvesting systems in the aqueous solution. Subsequently, two different fluorescence dyes Rhodamine B (RhB) and Sulforhodamine 101 (SR101) were introduced as energy acceptors into the solution of Pmvb-CB[8] respectively, to fabricate two different artificial light-harvesting systems. The obtained artificial light-harvesting systems can achieve an efficient energy transfer process from Pmvb-CB[8] to RhB or SR101 with high energy transfer efficiency.

Amphiphilicity-Controlled Polychromatic Emissive Supramolecular Self-Assemblies for Highly Sensitive and Efficient Artificial Light-Harvesting Systems

Dynamic sequential control of photoluminescence by supramolecular approaches has become a great issue in supramolecular chemistry. However, developing a systematic strategy to construct polychromatic photoluminescent supramolecular self-assemblies for improving the efficiency and sensitivity of artificial light-harvesting systems still remains a challenge. Here, a series of amphiphilicity-controlled supramolecular self-assemblies with polychromatic fluorescence based on lower-rim hexyl-modified sulfonatocalix[4]arene (SC4A6) and N-alkyl-modified p-phenylene divinylpyridiniums (PVPn, n = 2-7) as efficient light-harvesting platforms is reported. PVPn shows wide ranges of polychromatic fluorescence by co-assembling with SC4A6, whose emission trends significantly depend on the modified alkyl-chains of PVPn. The formed PVPn-SC4A6 co-assemblies as light-harvesting platforms are extremely sensitive for transferring the energy to two near-infrared emissive acceptors, Nile blue (NiB) and Rhodamine 800. After optimizing the amphiphilicity of PVPn-SC4A6 systems, the PVPn-SC4A6-NiB light-harvesting systems achieve an ultrasensitive working concentration for NiB (2 nm) and an ultrahigh antenna effect up to 91.0. Furthermore, the two different kinds of light-harvesting nanoparticles exhibit good performance on near-infrared imaging in the Golgi apparatus and mitochondria, respectively.

Noncovalent Polymerization-Activated Ultrastrong Near-Infrared Room-Temperature Phosphorescence Energy Transfer Assembly in Aqueous Solution

Noncovalent macrocycle-confined supramolecular purely organic room-temperature phosphorescence (RTP) is a current research hotspot. Herein, a high-efficiency noncovalent polymerization-activated near-infrared (NIR)-emissive RTP-harvesting system in aqueous solution based on the stepwise confinement of cucurbit[7]uril (CB[7]) and β-cyclodextrin-grafted hyaluronic acid (HACD), is reported. Compared with the dodecyl-chain-bridged 6-bromoisoquinoline derivative (G), the dumbbell-shaped assembly G⊂CB[7] presents an appeared complexation-induced RTP signal at 540 nm via the first confinement of CB[7]. Subsequently, benefitting from the stepwise confinement encapsulation of the β-cyclodextrin cavity, the subsequent noncovalent polymerization of the binary G⊂CB[7] assembly enabled by HACD can contribute to the further-enhanced RTP emission intensity approximately eight times in addition to an increased lifetime from 59.0 µs to 0.581 ms. Moreover, upon doping a small amount of two types of organic dyes, Nile blue or tetrakis(4-sulfophenyl)porphyrin as an acceptor into the supramolecular confinement assembly G⊂CB[7] @ HACD, efficient RTP energy transfer occurs accompanied by a long-lived NIR-emitting performance (680 and 710 nm) with a high donor/acceptor ratio. Intriguingly, the prepared RTP-harvesting system is successfully applied for targeted NIR imaging of living tumor cells by utilizing the targeting ability of hyaluronic acid, which provides a new strategy to create advanced water-soluble NIR phosphorescent materials.

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.

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.