Visualization and Manipulation of Solid-State Molecular Motions in Cocrystallization Processes

Fluorescence tracking of inter- and intramolecular motion in zwitterionic aggregate

Ionic aggregates are among the most common forms of matter, yet the investigation of their molecular motion is often constrained by the instability of isolated anions and cations, as well as the lack of real-time monitoring techniques. This study presents a zwitterionic strategy that integrates both cations and anions into one fluorescent organic framework, forming a zwitterionic molecule. The zwitterionic strategy simplifies the intricate cation-anion systems that are typically found in conventional inorganic salts and imparts them with fluorescent properties, facilitating real-time tracking of ionic-interaction-induced molecular motion within ionic aggregates. Specifically, a blue shift in the fluorescence wavelength signified changes in aggregate states due to intermolecular motion, whereas a decrease in intensity was linked to intramolecular-motion-caused conformational changes. This spontaneous molecular motion enabled dynamic switching of the excited state energy-decay pathway, leading to switchable color-light responses. Overall, the zwitterionic strategy offers a novel framework for exploring the properties and behaviors of molecules in ionic aggregates.

Investigation of Aggregation Induced Emission Mechanism of Tetrabenzoheptafulvalene Derivative by Spin-Flip Time-Dependent Density Functional Theory (SF-TDDFT)

This study explores the mechanism of aggregation-induced emission (AIE) in the tetrabenzoheptafulvalene derivative, 10,10',11,11'-tetrahydro-5,5'-bidibenzo[a,d][7]annulenylidene (abbreviated as THBDBA) in tetrahydrofuran (THF) solution. THBDBA is AIE-active because in THF solution, it emits significantly less emission (or almost non-emissive) and the fluorescence quantum yield increases by 230 times in aggregate state. We adopted spin-flip time-dependent density functional theory (SF-TDDFT), widely acknowledged for its ability to locate the conical intersection (CI) in medium to large-sized molecules (due to its balanced and reliable description of both ground and excited states and ability to capture double excitation and multireference characters at low computational cost). The functional used is long-range corrected ωPBEh (i. e., LRC-ωPBEh). The strategies used are the excited state deactivation processes by taking into account the S1/S0 surface crossing, referred to as the 'minimum energy conical intersection' (MECI). Reduction of oscillator strength near the minimum energy gap (MEG) structure or CI is also another parameter used to study fluorescence quenching. For the monomer (i. e., in solution), our findings reveal a significant reduction in oscillator strength (f) for de-excitation near the MEG structure and CI, which led us to conclude that in solution, the flapping motion of the phenyl rings plays a vital role to reach the CI. In a smaller scale, a dimer system was chosen to represent the aggregate state. The higher energy gap as well as higher f-value at MEG structure with just the model dimer system indicates that in the actual aggregate (or the crystal) the MECI might be absent. This is because in the aggregate the flapping motion of the phenyl rings will be highly restricted (because of the steric and electrostatic confinements by a large number of monomers from all sides), thereby favoring radiative transitions for energy dissipation. This study consequently elucidates the AIE mechanism of the chosen tetrabenzoheptafulvalene derivative, shedding light on its photophysical properties.

Boosting The Solid-State Luminescence of Phenazine Derivatives by Enhancing Intermolecular Hydrogen Bonds and π-π Interactions in Cocrystals

Six monosubstituted phenazine derivatives were designed and synthesized for constructing cocrystals to investigate their structure-property relationship. It was found that 2-substituted phenazines could form cocrystals with 2,6-dimethylphenylboronic acid (DBA). These cocrystals exhibited red-shifted and enhanced luminescence relative to their individual components, especially 2NP-DBA whose luminescence efficiency was nearly 100 times higher than that of 2NP. By analyzing the single-crystal structures of the cocrystals and their components, enhanced hydrogen bonds and π-π interactions between molecules were detected in cocrystals, which suppressed the nonradiative transition pathways. Consequently, all three cocrystals demonstrated enhanced luminescence with strong continuous π-π interactions, which differed from the previously reported luminescence enhancement resulting from the destruction of π-π interactions. An in-depth investigation of these cocrystals can not only provide a better understanding of the structure-property relationship of organic luminescent materials, but also help develop organic luminescent materials with intense solid-state luminescence and strong π-π interactions. In addition, the optical response of these cocrystals to acidic vapors has been successfully applied in anti-counterfeiting.

Organic Luminescent Cocrystals Based on Benzotriazole Derivatives: Synthesis, Characterization, Crystal Structure and Fluorescence Behavior

Organic cocrystals have garnered significant research attention owing to their distinctive properties and promising applications. However, challenges in molecular structure design and control of intermolecular interactions continue to impede further advancements. In this study, two novel cocrystals were successfully formed from a series of synthesized benzotriazole derivatives. The resulting cocrystals exhibit bright green and yellow fluorescence under 365 nm light. To elucidate the microstructure of the obtained cocrystals, systematic characterization techniques such as solid-state fluorescence emission spectroscopy, Single-crystal X-ray diffraction (SCXRD), Power X-ray diffraction (PXRD) and density functional theory (DFT) were performed. These benzotriazole-based cocrystals demonstrate distinct fluorescent responses to alkaline and acidic environments, respectively. Additionally, preliminary tests for fingerprint recognition yielded satisfactory results. These findings suggest that the two cocrystals hold potential applications in acid-alkali sensing, anti-counterfeiting labels, and smart material development, while also providing valuable insights for the design and optimization of solid-state luminescent materials.

New Molecular Photoswitch Based on the Conformational Transition of Phenothiazine Derivatives and Corresponding Triplet Emission Properties

Molecular photoswitch research has drawn much attention in the last century owing to its great potential in the development of smart materials. However, photoswitches suitable for constructing light-responsive luminescent materials remain limited, especially those involving triplet-state phosphorescence. Herein, we designed a novel molecular photoswitch based on the conformation transition of phenothiazine derivatives, minimizing steric hindrance (-CH3 > -Cl > -F) to regulate the conformation transition process while introducing a cyanobenzene acceptor to promote phosphorescence emission potential. When they were doped into a polymer matrix, varying photoswitch rates were achieved by incorporating different steric hindrance groups into phenothiazine or cyanobenzene groups, accompanied by photoresponsive room-temperature phosphorescence. This study is expected to greatly expand the diversity and applications of organic photoswitch molecules.

Spontaneous aggregation-enhanced electrochemiluminescence via galvanic strategy

Researchers unremittingly strive to develop innovative luminophores to enhance intrinsic electrochemiluminescence (ECL) performance. However, the potential to harness facile strategies, such as manipulating the physical properties of luminophores while retaining functional chemical properties to fabricate cost-effective ECL complexes, remains underexplored. Herein, we reported a novel and efficient one-step galvanic technique to actualize aggregation-enhanced ECL (AEECL) of ruthenium complexes. It marked the first instance of the galvanic process being employed to synthesize aggregate luminophores through electrostatic attraction. The ECL intensity and efficiency of the prepared ruthenium complexes with AEECL properties surpassed traditional ruthenium complexes by 8.9 and 13.6 times, respectively, outperforming most reported luminophores. Remarkably, the target luminophore exhibited high stability across varied scan rates and temperatures. Furthermore, a binder-free and carbon paper-based AEECL analytical device for lidocaine detection was fabricated, achieving a satisfactory detection limit (0.34 nM) and selectivity. The convenient modulation strategy of aggregate structure, along with the transformative leap from insufficient ECL to AEECL, bring forth a new revenue in aggregate science. This research also promises a universally applicable and versatile protocol for future biological analysis and bioimaging applications.

Integration of Wallach's Rule into Intermolecular Charge Transfer: A Visual Strategy for Chiral Purification

Exploring the molecular packing and interaction between chiral molecules, no matter single enantiomer or racemates, is important for recognition and resolution of chiral drugs. However, sensitive and non-destructive analysis methods are lacking. Herein, an intermolecular-charge transfer (ICT) based spectroscopy is reported to reveal the differences in interaction between the achiral acceptor 1,2,4,5-tetracyanobenzene (TCNB) and the chiral donors, including S, R, and racemic naproxen (S/R/rac-NAP). In this process, S-NAP+TCNB and R-NAP+TCNB display a narrower band gap attributed to the newly formed ICT state. In contrast, the mixed rac-NAP and TCNB exhibit almost no significant change due to the strong affinity between the stereoisomers according to the Wallach's rule. Thus, S/R-NAP can be easily distinguished from rac-NAP based on significantly different optical behavior. The single crystal analysis, infrared spectroscopy, fluorescence spectroscopy, and theoretical calculation of naproxen confirm the importance of carboxyl for this differentiation in molecular packing and interaction. In addition, the esterification derivatization of naproxen achieves the manipulation of the intermolecular interaction model of racemates from the absolute Wallach's rule to a coexisting form of Wallach's rule and ICT. Further, visualized chiral purification of naproxen by the simple cocrystallization method is achieved through the collaboration of ICT and Wallach's rule.

A universal strategy for constructing high-performance silica-based AIE materials for biomedical application

As an emerging fluorophore, aggregation-induced emission luminogens (AIEgens) have received widespread attention in recent years, but the inherent drawbacks of AIEgens, such as the poor water-solubility and insufficient fluorescence stability in complex environments, restrict their performance in practical applications. Herein, we report a universal strategy based on hydrophobic dendritic mesoporous silica (HMSN) that can integrate different AIE molecules to construct multi-color fluorescent AIE materials. Specifically, HMSN with central radial pores was used as a powerful carrier for direct loading AIE molecules and restricting their intramolecular motions. Due to the pore-domain restriction effect and hydrophobic interaction, the obtained silica-based AIE materials have bright fluorescence with a maximum quantum yield of 68.38%, high colloidal/fluorescence stability, and excellent biosafety. Further, these silica-based AIE materials can be conjugated with functional antibodies to obtain probes with different targetability. After integration with immunomagnetic beads, the prepared detection probes achieved the quantitative detection of cardiac troponin I with the limit of detection (LOD) of 0.508 ng/mL. Overall, the targeting probes stemming from silica-based AIE materials can not only achieve cell-specific imaging, but quantify the number of Jurkat cells (LOD = 270 cells/mL) to further determine the specific etiology of the disease.

A luminescent organic cocrystal for detecting 2,4-dinitroaniline

2,4-dinitroaniline (2,4DNBA), a significant hazardous chemical, is extensively used in industry and agriculture. The chemical accumulates in the environment for a long time, causing irreversible damage to the ecosystem. Currently, it is quite challenging to identify it by common analysis and detection techniques. Herein, a luminescent organic cocrystal (TCNB-8HQ) was prepared using 1,2,4,5-tetracyanobenzene (TCNB) as the electron acceptor and 8-hydroxyquinoline (8HQ) as the electron donor. The prepared TCNB-8HQ was used as a fluorescent probe with a fast and specific response to 2,4DNBA. This detection method possessed a linear range of 0.5-200 μmol/L with a detection limit as low as 0.085 μmol/L to detect 2,4DNBA in real samples with satisfactory spiking recovery. As revealed by fluorescence spectrum and UV-vis absorption spectrum, the detection mechanism involved competitive absorption between cocrystal material and 2,4DNBA. Moreover, the feasibility of the system was explored by preparing portable indicator strips for 2,4DNBA from organic cocrystal (TCNB-8HQ). This study not only provided an environmentally friendly gram-level preparation strategy to synthesize the fluorescent material but also investigated their application in chemical detection.

Stimuli-fluorochromic smart organic materials

Smart materials based on stimuli-fluorochromic π-conjugated solids (SFCSs) have aroused significant interest due to their versatile and exciting properties, leading to advanced applications. In this review, we highlight the recent developments in SFCS-based smart materials, expanding beyond organometallic compounds and light-responsive organic luminescent materials, with a discussion on the design strategies, exciting properties and stimuli-fluorochromic mechanisms along with their potential applications in the exciting fields of encryption, sensors, data storage, display, green printing, etc. The review comprehensively covers single-component and multi-component SFCSs as well as their stimuli-fluorochromic behaviors under external stimuli. We also provide insights into current achievements, limitations, and major challenges as well as future opportunities, aiming to inspire further investigation in this field in the near future. We expect this review to inspire more innovative research on SFCSs and their advanced applications so as to promote further development of smart materials and devices.

Understanding the AIE phenomenon of nonconjugated rhodamine derivatives via aggregation-induced molecular conformation change

The bottom-up molecular science research paradigm has greatly propelled the advancement of materials science. However, some organic molecules can exhibit markedly different properties upon aggregation. Understanding the emergence of these properties and structure-property relationship has become a new research hotspot. In this work, by taking the unique closed-form rhodamines-based aggregation-induced emission (AIE) system as model compounds, we investigated their luminescent properties and the underlying mechanism deeply from a top-down viewpoint. Interestingly, the closed-form rhodamine-based AIE system did not display the expected emission behavior under high-viscosity or low-temperature conditions. Alternatively, we finally found that the molecular conformation change upon aggregation induced intramolecular charge transfer emission and played a significant role for the AIE phenomenon of these closed-form rhodamine derivatives. The application of these closed-form rhodamine-based AIE probe in food spoilage detection was also explored.

Phosphorescence resonance energy transfer from purely organic supramolecular assembly

Phosphorescence energy transfer systems have been applied in encryption, biomedical imaging and chemical sensing. These systems exhibit ultra-large Stokes shifts, high quantum yields and are colour-tuneable with long-wavelength afterglow fluorescence (particularly in the near-infrared) under ambient conditions. This review discusses triplet-to-singlet PRET or triplet-to-singlet-to-singlet cascaded PRET systems based on macrocyclic or assembly-confined purely organic phosphorescence introducing the critical toles of supramolecular noncovalent interactions in the process. These interactions promote intersystem crossing, restricting the motion of phosphors, minimizing non-radiative decay and organizing donor-acceptor pairs in close proximity. We discuss the applications of these systems and focus on the challenges ahead in facilitating their further development.

Branched Copolymers with Tunable Clusteroluminescence in High Quantum Yield

A novel type of fluorescence without large conjugated structures called clusteroluminescence (CL) has attracted a great deal of attention in recent years. Despite its many advantages, the emerging CL still encounters difficulties of low quantum yield (QY) and preliminary mechanisms. In this work, the branched structure was introduced into poly(maleic anhydride-alt-vinyl acetate) by chain transfer monomer. The emission wavelength of the branched copolymers is red-shifted with the increase of branching degree, and the absolute QY of solids can reach up to 29.87%. Further characterizations reveal that the branched structure can improve the flexibility of polymer chains, thereby promoting the intrachain interactions of subgroups. Furthermore, in the case of branched anhydride copolymers, the equilibrium between intrachain interactions and nonradiative transitions holds a crucial significance in determining the QY. This endeavor not only offers new insights into the mechanism of CL but also presents a novel approach to surmount the low QY of anhydride copolymers, thus broadening the horizons of CLgens to unexplored domains.

A Nitro-Modified Luminescent Hydrogen-Bonded Organic Framework for Non-Contact and High-Contrast Sensing of Aromatic Amines

The global demand for intelligent sensing of aromatic amines has consistently increased due to concerns about health and the environment. Efforts to improve material design and understand mechanisms have been made, but highly efficient non-contact sensing with host-guest structures remains a challenge. Herein, we report the first example of non-contact, high-contrast sensing of aromatic amines in a hydrogen-bonded organic framework (HOF) based on a nitro-modified stereo building block. Direct observation of binding interactions of trapped amines is achieved, leading to charge separation-induced emission quenching between host and guests. Non-contact sensing of aniline and diphenylamine is realized with quenching efficiencies up to 91.7 % and 97.0 %, which shows potential for versatile applications. This work provides an inspiring avenue to engineer multifunctional HOFs via co-crystal preparations, thus enriching applications of porous materials with explicit mechanisms.

Highly efficient color-tunable organic co-crystals unveiling polymorphism, isomerism, delayed fluorescence for optical waveguides and cell-imaging

Photofunctional co-crystal engineering strategies based on donor-acceptor π-conjugated system facilitates expedient molecular packing, consistent morphology, and switchable optical properties, conferring synergic 'structure-property relationship' for optoelectronic and biological functions. In this work, a series of organic co-crystals were formulated using a twisted aromatic hydrocarbon (TAH) donor and three diverse planar acceptors, resulting in color-tunable solid and aggregated state emission via variable packing and through-space charge-transfer interactions. While, adjusting the strength of acceptors, a structural transformation into hybrid stacking modes ultimately results in color-specific polymorphs, a configurational cis-isomer with very high photoluminescence quantum yield. The cis-isomeric co-crystal exhibits triplet-harvesting thermally activated delayed fluorescence (TADF) characteristics, presenting a key discovery in hydrocarbon-based multicomponent systems. Further, 1D-microrod-shaped co-crystal acts as an efficient photon-transducing optical waveguides, and their excellent dispersibility in water endows efficient cellular internalization with bright cell imaging performances. These salient approaches may open more avenues for the design and applications of TAH based co-crystals.

Aggregation-Induced Emission (AIE), Life and Health

Light has profoundly impacted modern medicine and healthcare, with numerous luminescent agents and imaging techniques currently being used to assess health and treat diseases. As an emerging concept in luminescence, aggregation-induced emission (AIE) has shown great potential in biological applications due to its advantages in terms of brightness, biocompatibility, photostability, and positive correlation with concentration. This review provides a comprehensive summary of AIE luminogens applied in imaging of biological structure and dynamic physiological processes, disease diagnosis and treatment, and detection and monitoring of specific analytes, followed by representative works. Discussions on critical issues and perspectives on future directions are also included. This review aims to stimulate the interest of researchers from different fields, including chemistry, biology, materials science, medicine, etc., thus promoting the development of AIE in the fields of life and health.

Natural Coumarin Isomers with Dramatically Different AIE Properties: Mechanism and Application

Aggregation-induced emission luminogens (AIEgens) are of great importance in optoelectronics and biomedical fields. However, the popular design philosophy by combining rotors with traditional fluorophores limits the imagination and structural diversity of AIEgens. Inspired by the fluorescent roots of the medicinal plant Toddalia asiatica, we discovered two unconventional rotor-free AIEgens, 5-methoxyseselin (5-MOS) and 6-methoxyseselin (6-MOS). Interestingly, a slight structural difference of the coumarin isomers leads to completely contrary fluorescent properties upon aggregation in aqueous media. Further mechanism investigation indicates that 5-MOS forms different extents of aggregates with the assistance of protonic solvents, leading to electron/energy transfer, which is responsible for its unique AIE feature, i.e., reduced emission in aqueous media but enhanced emission in crystal. Meanwhile, for 6-MOS, the conventional restriction of the intramolecular motion (RIM) mechanism is responsible for its AIE feature. More interestingly, the unique water-sensitive fluorescence property of 5-MOS enables its successful application for wash-free mitochondria imaging. This work not only demonstrates an ingenious tactic to seek new AIEgens from natural fluorescent species but also benefits the structure design and application exploration of next-generation AIEgens.

Tunable Red Clusteroluminescence Polymers Prepared by a Simple Heating Process

Clusteroluminescence (CL) has drawn much attention in recent years. However, the design of red emission clusteroluminogens (CLgens) with tunable CL is still in its infancy. Herein, we report a simple heating process to prepare red emission poly(maleic anhydride-alt-vinyl acetate) (PMV) derivatives with a tunable maximum emission wavelength between 620 and 675 nm. First, heating above the glass transition temperature (T_g) would promote the movement of polymer chains and facilitate the formation of clusters in both solid and solution states. Then, heating beyond the decomposition temperature at which vinyl acetate converts into C═C is favorable to the formation of new clusters and large through-space conjugation among subgroups in polymer chains. Their synergistic effects realize the adjustable emission wavelength and higher quantum yield of polymers. Additionally, low-cost and eco-friendly core-shell PMV particles are prepared as agricultural light conversion agents and exhibit great compatibility with polyethylene.

The Effect of Molecular Conformations and Simulated "Self-Doping" in Phenothiazine Derivatives on Room-Temperature Phosphorescence

The research of purely organic room-temperature phosphorescence (RTP) materials has drawn great attention for their wide potential applications. Besides single-component and host-guest doping systems, the self-doping with same molecule but different conformations in one state is also a possible way to construct RTP materials, regardless of its rare investigation. In this work, twenty-four phenothiazine derivatives with two distinct molecular conformations were designed and their RTP behaviors in different states were systematically studied, with the aim to deeply understand the self-doping effect on the corresponding RTP property. While the phenothiazine derivatives with quasi-axial (ax) conformation presented better RTP performance in aggregated state, the quasi-equatorial (eq) ones were better in isolated state. Accordingly, the much promoted RTP performance was achieved in the stimulated self-doping state with ax-conformer as host and eq-one as guest, demonstrating the significant influence of self-doping on RTP effect.

Development of Yellow-to-Orange Photoluminescence Molecules Based on Alterations in the Donor Units of Fluorinated Tolanes

Since the aggregation-induced emission (AIE) phenomenon was first reported by Tang et al., much effort has been devoted to the development of solid-state luminescent molecules by chemists worldwide. Our group successfully developed fluorinated tolanes as novel compact π-conjugated luminophores with blue photoluminescence (PL) in the crystalline state. Moreover, we reported the yellow-green PL molecules based on their electron-density distributions. In the present study, we designed and synthesized fluorinated tolanes with various amine-based donors and evaluated their photophysical properties. The carbazole-substituted fluorinated tolane exhibited strong PL in the solution state, whereas piperidine- or phenothiazine-substituted fluorinated tolanes showed a dramatic decrease in PL efficiency. Notably, fluorinated tolanes with piperidine or phenothiazine substituents displayed yellow-to-orange PL in the crystalline state; this may have occurred because these tolanes exhibited tightly packed structures formed by intermolecular interactions, such as H···F hydrogen bonds, which suppressed the non-radiative deactivation process. Moreover, fluorinated tolanes with amine-based donors exhibited AIE characteristics. We believe that these yellow-to-orange solid PL molecules can contribute to the development of new solid luminescent materials.

Boosting Near-Infrared Photothermal Conversion by Intermolecular Interactions in Isomeric Cocrystals

Organic cocrystal exhibits excellent photothermal conversion (PTC), but how the intermolecular interactions of cocrystals regulate the PTC is obscure. Here, two isomeric donor molecules (phenanthrene and anthracene) and two electron-withdrawing molecules (7,7,8,8,8-tetracyanodimethylquinone and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinone dimethane) are self-assembled into the four cocrystals (PTQ, PFQ, ATQ, and AFQ). By changing the molecular configuration of the donor and the electron-withdrawing ability of the acceptor, the intrinsic influencing factors of the intermolecular interaction on the PTC were explored. Under near-infrared laser (808 nm) irradiation, the PTC efficiencies of PTQ, PFQ, AFQ, and ATQ are 35.85, 44.74, 57.00, and 60.53%, respectively. Based on the single-crystal X-ray diffraction, ultrafast time-resolved transient absorption, and excited-state theoretical calculations, we found that the π-π stacking in ATQ and AFQ is conducive to promoting the near-infrared light-harvesting ability and the p-π interaction of cocrystals can regulate the nonradiative rotation of -C(C≡N)₂ groups, resulting in a tunable near-infrared PTC via the isomeric cocrystals. Accordingly, the evaporation rate of the porous polyurethane-AFQ foam can reach 1.33 kg·m^-2·h^-1 in the simulated solar-driven water evaporation system. This work provides a strategy to boost the PTC by the intermolecular interactions of cocrystal materials.

Secondary through-space interactions facilitated single-molecule white-light emission from clusteroluminogens

Clusteroluminogens refer to some non-conjugated molecules that show visible light and unique electronic properties with through-space interactions due to the formation of aggregates. Although mature and systematic theories of molecular photophysics have been developed to study conventional conjugated chromophores, it is still challenging to endow clusteroluminogens with designed photophysical properties by manipulating through-space interactions. Herein, three clusteroluminogens with non-conjugated donor-acceptor structures and different halide substituents are designed and synthesized. These compounds show multiple emissions and even single-molecule white-light emission in the crystalline state. The intensity ratio of these emissions is easily manipulated by changing the halide atom and excitation wavelength. Experimental and theoretical results successfully disclose the electronic nature of these multiple emissions: through-space conjugation for short-wavelength fluorescence, through-space charge transfer based on secondary through-space interactions for long-wavelength fluorescence, and room-temperature phosphorescence. The introduction of secondary through-space interactions to clusteroluminogens not only enriches their varieties of photophysical properties but also inspires the establishment of novel aggregate photophysics for clusteroluminescence.

Although mature and systematic theories of molecular photophysics have been developed, it is still challenging to endow clusteroluminogens (CLgens) with designed photophysical properties by manipulating through-space interactions. Here, the authors design three CLgens that show multiple emissions and white-light emission in the crystalline state, and emphasize the important role of secondary through-space interactions between the acceptor and non-conjugated donor units.

Novel Quinolizine AIE System: Visualization of Molecular Motion and Elaborate Tailoring for Biological Application

Molecular motions are ubiquitous in nature and they immutably play intrinsic roles in all actions. However, exploring appropriate models to decipher molecular motions is an extremely important but very challenging task for researchers. Considering aggregation-induced emission (AIE) luminogens possess their unique merits to visualize molecular motions, it is particularly fascinating to construct new AIE systems as models to study molecular motion. Herein, a novel quinolizine (QLZ) AIE system was constructed based on the restriction intramolecular vibration (RIV) mechanism. It was demonstrated that QLZ could act as an ideal model to visualize single-molecule motion and macroscopic molecular motion via fluorescence change. Additionally, further elaborate tailoring of this impressive core achieved highly efficient reactive oxygen species production and realized fluorescence imaging-guided photodynamic therapy applications, which confirms the great application potential of this new AIE-active QLZ core. Therefore, this work not only provides an ideal model to visualize molecular motion but also opens a new way for the application of AIEgens.

In Situ Visualization of Reversible Diels-Alder Reactions with Self-Reporting Aggregation-Induced Emission Luminogens

The dynamic reversible Diels-Alder (DA) reactions play essential roles in both academic and applied fields. Currently, in situ visualization and direct monitoring of the formation and cleavage of covalent bonds in DA reactions are hampered by finite compatibility and expensive precise instruments, especially limited in solid reactions. We herein report a fluorescence system capable of in situ visualization by naked eyes and monitoring DA/retro-DA reactions. With the fluorescence quenching effect, the synthesized TPEMI could work as an innovative self-indicator for both DA termination and retro-DA occurrence. The fluorescence increases during DA reactions, and the mechanism is investigated to establish qualitative and quantitative relations. Besides rapid screening of reaction conditions and monitoring of DA exchange processes, the TPEMI fluorescence system can visualize heterogeneous and solid-state reactions with the AIE character. The TPEMI platform is expected to offer novel insights into reversible DA processes and dynamic covalent chemistry.

Ligand regulated metal–organic frameworks for synergistic photoredox and nickel catalysis

Synergistic photoredox and nickel catalytic cross-coupling systems have created a great attraction as a promising methodology to produce the aryl C−N bonds under mild conditions as well as extreme challenge,...

Hydrogen Bond Organic Frameworks as a Novel Electrochemiluminescence Luminophore: Simple Synthesis and Ultrasensitive Biosensing

Nowadays, continuous efforts have been devoted to searching highly efficient electrochemiluminescence (ECL) emitters for applications in clinical diagnosis and food safety. In this work, triazinyl-based hydrogen bond organic frameworks (Tr-HOFs) were synthesized by N···H hydrogen bond self-assembly aggregation, where 6,6'-(1,4-phenylene)bis(1,3,5-triazine-2,4-diamine) (phenyDAT) was prepared via the cyclization reaction and behaved as a novel ligand. Impressively, the resulting Tr-HOFs showed strong ECL responses with highly enhanced ECL efficiency (21.3%) relative to the Ru(bpy)₃²⁺ standard, while phenyDAT hardly showed any ECL emission in aqueous phase. The Tr-HOFs innovatively worked as a new ECL luminophore to construct a label-free biosensor for assay of kanamycin (Kana). Specifically, the ECL response greatly weakened upon assembly of captured DNA with ferrocene (cDNA-Fc) onto the Tr-HOFs-modified electrode, while the ECL signals were adversely recovered by releasing linked DNA (L-DNA) from double-stranded DNA (dsDNA, hybridization of aptamer DNA (aptDNA) with L-DNA) due to the specific recognition of Kana with the aptDNA combined by the linkage of L-DNA and cDNA-Fc on the electrode. The as-built sensor showed a broadened linear range (1 nM-10 μM) and a limit of detection (LOD) down to 0.28 nM, which also displayed satisfactory results in the analysis of Kana in the milk and diluted human serum samples. This work offers a novel pathway to design an ECL emitter with organic molecules, holding great promise in biomedical analysis and food detection.

Thermal Expansion Properties and Mechanochemical Synthesis of Stoichiometric Cocrystals Containing Tetrabromobenzene as a Hydrogen- and Halogen-Bond Donor

The solution and mechanochemical synthesis of two cocrystals that differ in the stoichiometric ratio of the components (stoichiometric cocrystals) is reported. The components in the stoichiometric cocrystals interact through hydrogen or hydrogen/halogen bonds and differ in π-stacking arrangements. The difference in structure and noncovalent interactions affords dramatically different thermal expansion behaviors in the two cocrystals. At certain molar ratios, the cocrystals are obtained concomitantly; however, by varying the ratios, a single stoichiometric cocrystal is achieved using mechanochemistry.