Preparation of a fixed-tetraphenylethylene motif bridged ditopic benzo-21-crown-7 and its application for constructing AIE supramolecular polymers

Rhodamine/Cucurbit[8]uril Co-assembled supramolecular aggregates realize the precise and enhancive bioimaging of plant active signals

Fluorescent molecular probes are commonly used to detect active substances. However, in variable living microenvironmental systems, most of conventional aromatic fluorescent probes often suffer from aggregation-caused quenching (ACQ) due to π-π stacking, which severely limit their selective recognition and bioimaging functions. To tackle this challenge, we devise an structurally novel small-molecule-adamantane-modified Rhodamine probe (RAA) and employ a predictable cucurbit[8]uril (Q[8])-involved host-guest supramolecular strategy to optimize molecular aggregation behaviors at the molecular level, thereby creating supramolecular aggregates (RAA@Q[8]) as an innovative fluorescent probe. This encouraging result is important for precise and efficient detection of plant signaling molecules such as salicylic acid (SA) in various environments. Experimental investigations found that RAA@Q[8] was 2.2-fold more sensitive than RAA for detecting SA, with high selectivity and anti-interference, and a low detection limit of 3.0 × 10-8 M. Importantly, RAA@Q[8] realizes the enhanced, precise recognition and bioimaging of SA on pea sprouts and HEK-293 cells. This study offers a guidance for developing efficient chemosensors from small-molecule conception to ultrasensitive supramolecular fluorescent probes that are opposite to the intractable ACQ obstacle.

A Crystalline 3D Supramolecular Polymer Constructed by Clamparene-Based Controllable Self-Assembly and Its Application in Photothermal Conversion

The development of well-defined three-dimensional supramolecular polymers presents significant challenges, particularly in achieving crystalline state structures. This study addresses this challenge by presenting the construction of a crystalline three-dimensional supramolecular polymer through the self-assembly of clamparene (CLP) and a naphthalene diimide derivative (NDIOH) in the solid state. The hierarchical self-assembly progresses from one-dimensional linear supramolecular polymers to two-dimensional supramolecular polymers and ultimately to a crystalline three-dimensional supramolecular polymer. Moreover, the prepared crystalline three-dimensional supramolecular polymer demonstrates effective photothermal conversion. This work advances the understanding and design of functional three-dimensional supramolecular polymers in the crystalline state.

Aggregation-induced emission-active supramolecular polymers: from controlled preparation to applications

Supramolecular polymers are typical self-assemblies, in which repeating monomer units are bonded together with dynamic and reversible noncovalent interactions. Supramolecular polymers can combine the advantages of polymer science and supramolecular chemistry. Aggregation-induced emission (AIE) means that a molecule remains faintly emissive in the dispersed state but intensively luminescent in a highly aggregated state. AIE has brought new opportunities and further development potential to the field of polymeric chemistry. The integration of AIE luminogens with supramolecular interactions can provide new vitality for supramolecular polymers. Therefore, it is essential for scientists to understand the preparation and applications of AIE-active supramolecular polymers. This review focuses on the recent advanced progress in the preparation of AIE-active supramolecular polymers. In addition, we summarize the newly developed supramolecular polymers with an AIE nature and their applications in chemical sensing, and in vitro and in vivo imaging, as well as the visualization of their structure and properties. Finally, the development trends and challenges of AIE-active supramolecular polymers are prospected.

A Highly Efficient Supramolecular Polymer-Based Singlet Oxygen Generator for Photocatalytic Minisci Alkylation

Supramolecular polymers, with their specific functional units and structures, can effectively enhance the absorption and utilization of light energy, thereby facilitating more efficient photocatalytic organic reactions. In the present work, we constructed a supramolecular polymer consisting of benzothiazole derivatives (BTBP) and cucurbit[8]uril (CB[8]). The BTBP monomer, known for its unique chemical structure and properties, has been found to exhibit a remarkable capability in generating singlet oxygen (1O2). As a result of the constraining impact of the macrocyclic molecule, the inclusion of CB[8] resulted in an effective enhancement in the ability to generate 1O2 while forming supramolecular polymer BTBP-CB[8]. When evaluating the quantum yield of 1O2 using Rose Bengal (RB) as a reference photosensitizer (75% in water), BTBP-CB[8] demonstrated an enhanced 1O2 quantum yield compared to BTBP, with an impressive yield of 152.4%, demonstrating that the formation of supramolecular polymer contributes to its ability to generate 1O2. Subsequently, BTBP-CB[8], a highly efficient 1O2 generator, was employed for the photocatalytic Minisci alkylation reaction, resulting in an impressive reaction yield of up to 89%. The supramolecular polymer strategies employed in the construction of photocatalytic systems have exhibited remarkable efficacy in the production of 1O2, underscoring their immense prospects in photocatalysis.

Construction of an Artificial Sequential Light-Harvesting System and White-Light Material Utilizing Supramolecular Gels

The molecular (pyren-1-yloxy)-acetic acid (Py) with excellent fluorescence properties was synthesized from 1-hydroxypyrene (Hp) and formed a supramolecular gel with an acid-base stimulus response in dimethylformamide and water. On the basis of gel, the fluorescent dye perylene 3, 9-dicarbxylic acid, and rhodamine 6g were added successively to construct a step-by-step artificial light-harvesting system, so that the fluorescence color changed from blue-purple to green to red, and white light emission was realized by adjusting the ratio of donors and acceptors.

Pillar[5]arene-Based Fluorescent Supramolecular Polymers Without Conventional Chromophores

Fluorescent supramolecular polymers have garnered significant attention due to their successful integration of supramolecular polymers and fluorescence, offering vast potential for applications in sensing, imaging, optoelectronics, and photonics. In this study, we present a novel supramolecular polymer based on P5-OH, derived from mono-substituted pillararene macrocycles. Notably, these formed supramolecular polymeric aggregates exhibit a prominent blue emission, representing a rare instance of fluorescent polymers devoid of conventional chromophores. Furthermore, through the modification of alkyl chain ending groups attached to pillar[5]arenes, slight shifts in the emission peak could be observed. This research expands the scope of functional supramolecular polymeric systems utilizing pillararenes, providing valuable insights for the design of innovative luminescent materials and optical devices.

A rational design of polymers through donor modulation to weaken the aggregation-caused quenching effect for NIR-II fluorescence imaging

The great tissue penetration depth and low tissue autofluorescence of NIR-II fluorescence imaging make it attractive for in vivo diagnosis. However, the aggregation-caused quenching (ACQ) effect is among the dominant obstacles that weaken NIR-II imaging and restrict its application. Herein, the donor unit, 2,8-dibromo-6H,12H-5,11-methanodibenzo[b,f] [1,5]diazocine with a V-configuration, was introduced to prepare the donor-acceptor (D-A) polymer P-TB with a twisted backbone, while the planar D-A polymer P-TP was used as a control. P-TB and P-TP were prepared by Stille Coupling with DPP as the acceptor. The main absorption peaks of P-TB and P-TP are located at 610 nm and 640 nm, and the emission peaks of P-TB and P-TP are 1060 nm and 930 nm, respectively. Significantly, the V-shaped P-TB showed no obvious ACQ effect within 600 μM, and the same phenomenon was demonstrated during in vivo NIR-II imaging in mice, which proves that the introduction of V-configuration donor units is beneficial for weakening the ACQ effect. This work outlines a prospective tactic for the design of conventional NIR-II fluorescent polymers by modulating the configuration of the donor units.

The aqueous supramolecular chemistry of crown ethers

This mini-review summarizes the seminal exploration of aqueous supramolecular chemistry of crown ether macrocycles. In history, most research of crown ethers were focusing on their supramolecular chemistry in organic phase or in gas phase. In sharp contrast, the recent research evidently reveal that crown ethers are very suitable for studying abroad range of the properties and applications of water interactions, from: high water-solubility, control of Hofmeister series, "structural water", and supramolecular adhesives. Key studies revealing more details about the properties of water and aqueous solutions are highlighted.

Artificial light-harvesting systems based on supramolecular self-assembly multi-component metallogels

This paper proposes a strategy for fabricating new artificial light-harvesting systems (ALHSs) based on supramolecular multi-component metallogels. Al³⁺ was introduced into a solution of an acylhydrazone compound (L) in DMSO or DMF to form the L-Al³⁺ assembly. After adding Al³⁺ to the L solution, a noticeable blue shift appeared in the fluorescence spectra of L. Moreover, L could form a gel (L-B-gel) with 1,3:2,4-dibenzylidene sorbitol (B) in a DMSO-H₂O binary solution. Finally, we obtained a multi-component metallogel (L-Al³⁺-B-gel) and successfully fabricated two ALHSs (L-Al³⁺/rhodamine 6G (Rh6G) and L-Al³⁺/rhodamine B (RhB)). In these systems, the L-Al³⁺ supramolecular assembly acts as the donor, while Rh6G and RhB act as acceptors. Additionally, we confirmed an energy-transfer process from the L-Al³⁺ component to Rh6G and RhB separately. The proposed fabrication strategy will facilitate the development of ALHSs.

Stereoisomeric engineering of aggregation-induced emission photosensitizers towards fungal killing

Fungal infection poses and increased risk to human health. Photodynamic therapy (PDT) as an alternative antifungal approach garners much interest due to its minimal side effects and negligible antifungal drug resistance. Herein, we develop stereoisomeric photosensitizers ((Z)- and (E)-TPE-EPy) by harnessing different spatial configurations of one molecule. They possess aggregation-induced emission characteristics and ROS, viz. ¹O₂ and O₂^-• generation capabilities that enable image-guided PDT. Also, the cationization of the photosensitizers realizes the targeting of fungal mitochondria for antifungal PDT killing. Particularly, stereoisomeric engineering assisted by supramolecular assembly leads to enhanced fluorescence intensity and ROS generation efficiency of the stereoisomers due to the excited state energy flow from nonradiative decay to the fluorescence pathway and intersystem (ISC) process. As a result, the supramolecular assemblies based on (Z)- and (E)-TPE-EPy show dramatically lowered dark toxicity without sacrificing their significant phototoxicity in the photodynamic antifungal experiments. This study is a demonstration of stereoisomeric engineering of aggregation-induced emission photosensitizers based on (Z)- and (E)-configurations.

Self-assembled Fluorescent Nanoparticles with Tunable LCST Behavior in Water

The development of stimuli-responsive fluorescent materials in water based on organic molecule has drawn significant interest. Herein, we designed and synthesized an amphiphilic molecule M containing a fixed tetraphenylethylene moiety (FTPE) as hydrophobic part and tri(ethylene glycol) (TEG) chains as hydrophilic part. Notably, the FTPE moiety is aggregation-induced emission (AIE) active, while the TEG chains are thermo-responsive. M can self-assemble into fluorescent nanoparticles (NPs) in water, which showed lower critical solution temperature (LCST) behavior. Moreover, its clouding point can be reversibly tuned upon the concentration variation. Interestingly, the NPs can be acted as a fluorescence thermometer in aqueous media owing to their unique AIE and LCST behaviors. Our work herein not only provides an integration strategy to construct stimuli-responsive fluorescent materials but also shows great potential in biological applications including bioimaging and biosensors.

Hierarchical lyotropic liquid crystalline behaviors of supramolecular polymers influenced by alkyl chain branching

The peripheral chain branching in monomeric structures influences the hierarchical supramolecular assembly and lyotropic liquid crystalline properties.

Crown Ether-Based Supramolecular Polymers: From Synthesis to Self-Assembly

Supramolecular polymers not only possess many advantages of traditional polymers, but also have many unique characteristics. Supramolecular polymers can be constructed by self-assembly of various noncovalent interactions. Host-guest interaction, as one important type of noncovalent interactions, has been widely applied to construct supramolecular polymers. From the perspective of classification of the recognition system motifs, host-guest recognition motifs mainly include crown ether, cyclodextrin, calixarene, cucurbituril, and pillararene-based host-guest recognition pairs. Crown ethers, as the first-generation macrocyclic hosts, have played a very important part in the development of supramolecular chemistry. Due to the easy modification of crown ethers, various crown ether derivatives have been prepared by attaching some functional groups to the edges of crown ethers, which endowed them with some interesting properties and made them ideal candidates for the fabrication of supramolecular polymers. This review gives a review of the preparation of crown ether-based supramolecular polymers (CSPs) and summarizes crown ether-based recognition pairs, organization methods, topological structures, stimuli-responsiveness, and functional characteristics.

Efficient artificial light-harvesting system constructed from supramolecular polymers with AIE property

Supramolecular luminescent materials in water have attracted much interest due to their excellent tunability, multi-color emission, and environment-friendly behavior. However, hydrophobic chromophores are often affected by poor solubility and aggregation-caused quenching effects in aqueous media. Herein, we report a water-phase artificial light-harvesting system based on an AIE-type supramolecular polymer. Specifically, dispersed nanoparticles in water were prepared from an AIE chromophore-bridged ditopic ureidopyrimidinone (M) based supramolecular polymer with the assistance of surfactants. By co-assembling the hydrophobic chromophores NDI as energy acceptor into the nanocarriers, artificial light-harvesting systems (M-NDI) could be successfully constructed, exhibiting efficient energy transfer and high antenna effects. Furthermore, the spectral emission of the system could be continuously tuned with a relatively small number of acceptors. This work develops an efficient supramolecular light-harvesting system in water, which has potential applications in dynamic luminescent materials.

Regulation of the Switchable Luminescence of Tridentate Platinum(II) Complexes by Photoisomerization

Organoplatinum (II) complexes are promising candidates for the construction of smart supramolecular materials due to their unique flat structures. This accompanied by intriguing luminescent properties, prompts the molecules to aggregate after external stimuli. Nevertheless, the utilization of photo-responsive subunits to modulate their assemble behaviors and functions are still rarely explored. In this work, azobenzene (azo)-appended tridentate platinum (II) complexes with different linkers have been designed and synthesized. The intermolecular hydrogen bonding, π-π stacking, and metal-metal interactions were finely controlled through the tiny alteration of the linkers, which was found to play a vital role in self-assembly, and photophysical and photoisomerization properties. Some of them exhibited dual emission bands originating from metal-perturbed triplet intraligand (3IL) and metal-metal to ligand charge transfer (3MMLCT) excited states due to the different intermolecular interactions. Based on this, the manipulation of switchable luminescence as well as the controllable morphologies have been realized by photoisomerization.