An Intelligent AIEgen with Nonmonotonic Multiresponses to Multistimuli

An Acid-Responsive Fluorescent Molecule for Erasable Anti-Counterfeiting

A tetraphenylethylene (TPE) derivative, TPEPhDAT, modified by diaminotriazine (DAT), was prepared by successive Suzuki-Miyaura coupling and ring-closing reactions. This compound exhibits aggregation-induced emission enhancement (AIEE) properties in the DMSO/MeOH system, with a fluorescence emission intensity in the aggregated state that is 5-fold higher than that of its counterpart in a dilute solution. Moreover, the DAT structure of the molecule is a good acceptor of protons; thus, the TPEPhDAT molecule exhibits acid-responsive fluorescence. TPEPhDAT was protonated by trifluoroacetic acid (TFA), leading to fluorescence quenching, which was reversibly restored by treatment with ammonia (on-off switch). Time-dependent density functional theory (TDDFT) computational studies have shown that protonation enhances the electron-withdrawing capacity of the triazine nucleus and reduces the bandgap. The protonated TPEPhDAT conformation became more distorted, and the fluorescence lifetime was attenuated, which may have produced a twisted intramolecular charge transfer (TICT) effect, leading to fluorescence redshift and quenching. MeOH can easily remove the protonated TPEPhDAT, and this acid-induced discoloration and erasable property can be applied in anti-counterfeiting.

Excreted albumin of diabetic microalbuminuria cases exhibits pseudo esterase activity: A new way to explore microalbuminuria, perhaps with more information

BACKGROUND

Microalbuminuria is associated with several clinical conditions of public health concern. Particularly in diabetic patients, there is routine microalbuminuria screening to understand whether the renal complication has progressed to the microalbuminuria stage or not. Therefore, microalbuminuria detection is a matter of considerable interest. For such detection, the clinical labs rely on immunochemical methods. Nevertheless, the immunochemical methods are believed to be less sensitive for the purpose. So, the need arises for continuous research in the field. We believe that pseudoesterase activity of the excreted albumin in microalbuminuria cases is a potential target. This aspect is investigated here and it is shown that the excreted albumin in diabetic microalbuminuria cases retains its pseudoesterase activity, unlike the overt albuminuria cases.

METHODS

The cases of diabetic nephropathy and healthy controls were included in the study. The patients were divided into diabetic controls microalbuminuria, and overt albuminuria group considering the albumin to creatinine ratio (ACR). The urinary proteins of the cases were isolated by centrifugation. The obtained protein pellet was then checked for pseudoesterase activity by electrophoretic and fluorescence-based methods. The CD spectroscopy and LC-MS study was carried out to show the suitability of the substrate for the detection of albumin pseudoesterase activity. To further, understand the structure-function relation, molecular docking studies were carried out.

RESULTS

From the CD and LC-MS study the suitability of the used substrate was confirmed. The electrophoretic and fluorescence study showed that the protein of the microalbuminuria group retained the pseudoesterase activity whereas the same is lost in the overt albuminuria group. The molecular docking studies indicated that a change in albumin structure may result in a change in its pseudoesterase activity.

CONCLUSION

The urinary protein of diabetic microalbuminuria cases exhibits pseudoesterase activity. It distinguishes the excreted protein in the diabetic albuminuria group and the overt albuminuria group. This is the first study that showed the retention of pseudoesterase property in excreted albumin. Further, in this study a simple test is developed that distinguishes the excreted albumin in the microalbuminuria group and overt albuminuria group.

Toward High Contrast and Noninvasive Fluorescence Switches via an O-Fused Ring 5,7-Dihydroxy-4-methyl-2,2,3-triphenylbenzofuran-6(2H)-one Strategy

An unprecedented O-fused ring 5,7-dihydroxy-4-methyl-2,2,3-triphenylbenzofuran-6(2H)-one (3) was first time synthesized. Further, a series of novel dialkyl/fluoroalkyl derivatives of compound 3, 5,7-dialkoxy/fluoroalkoxy-4-methyl-2,2,3-triphenylbenzofuran-6(2H)-one, were obtained with noninvasive fluorescence switching characteristics and aggregation-induced emission properties. Compared with fluoroalkyl derivatives, the alkyl analogs exhibited a significant bathochromic shift in solid-state fluorescence emission. Notably, these noninvasive fluorescent molecular switches could be facilely tuned through light and heat stimulation, which successfully achieved high contrast and reversible fluorescent emission between orange and yellow endowing them with potential applications in data encryption materials. In addition, the single crystal data of compounds 3 and 7-CF3 displayed weak intermolecular interactions in different directions, resulting in twisted conformation and antiparallel slip stacking. Interestingly, the polymer dimethyl silicone film doped with 7-C3F7 also showed an evident light-responsive behavior, meeting the criterion for fluorescent materials in the optical field.

Tandem Four-Component Reaction to Access Fused Polycycles Exhibiting Aggregation-Enhanced Through-Space Charge Transfer Emission

Rapid construction of new fluorescence emitters is essential in advancing synthetic luminescent materials. This study illustrated a piperidine-promoted reaction of chiral dialdehyde with benzoylacetonitrile and malonitrile, leading to the formation of the 6/6/7 fused cyclic product in good yield. The proposed reaction mechanism involves a dual condensation/cyclization process, achieving the formation of up to six bonds for fused polycycles. The single crystal structure analysis revealed that the fused cyclic skeleton contains face-to-face naphthyl and cyanoalkenyl motifs, which act as the electronic donor and acceptor, respectively, potentially resulting in through-space charge transfer (TSCT) emission. While the TSCT emissions were weak in solution, a notable increase in luminescence intensity was observed upon aggregation, indicating bright fluorescent light. A series of theoretical analyses further supported the possibility of spatial electronic communication based on frontier molecular orbitals, the distance of charge transfer, and reduced density gradient analysis. This work not only provides guidance for the one-step synthesis of complex polycycles, but also offers valuable insights into the design of aggregation-enhanced TSCT emission materials.

Solvatochromic and Proton-Responsive characteristics of Bi-1,3,4-Oxadiazole derivatives with symmetric dimethylamino substitution

D-A molecules find extensive use in intelligent stimulus-response systems due to their exceptional attributes, including high sensitivity, rapid response, wide compatibility, and structural adaptability. The strength of Intramolecular Charge Transfer (ICT) plays a pivotal role in determining the performance of these devices. To enhance the ICT strength and explore new applications for D-A molecules, we meticulously designed a pair of symmetric dimethylamino-substituted bi-1,3,4-oxadiazole derivatives (DMAOXD and DMAOXDBEN). These symmetric D-A-A-D molecules, with strong electron donor terminals, displayed a modest redshift of less than 25 nm in the UV-vis absorption spectra. However, there was a significant redshift in the emission spectra (140 nm for DMAOXD and 170 nm for DMAOXDBEN) when transitioning from cyclohexane to dimethyl sulfoxide, indicating a pronounced ICT characteristic. Theoretical calculations support the idea that the dimethylaminophenyl unit serves as an electron donor in both DMAOXD and DMAOXDBEN, while the 1,3,4-oxadiazole and central benzene ring act as acceptors. The pronounced ICT characteristic observed in DMAOXD and DMAOXDBEN can be attributed to long-distance electron transfer. Additionally, it's noteworthy that the emission of DMAOXD and DMAOXDBEN solution samples can be quenched by adding trifluoroacetic acid (TFA) and restored by the addition of triethylamine (TEA). Inspired by this, a pattern created with ink samples containing DMAOXD and DMAOXDBEN can be concealed through fumigation with TFA and subsequently revealed by treating them with TEA, suggesting their potential use in data encryption.

p-Phenylenediamine-derived carbon nanodots for probing solvent interactions

Carbon nanodots, the luminescent nanoparticles of carbon with size restriction below 10 nm, have attracted inordinate attention in materials science due to their widespread applications in optoelectronic and biological fields. Low toxicity and facile synthesis pathways render them favourites in the above-mentioned areas in the context of green chemistry. This work presents fine applications of p-phenylenediamine-derived carbon nanodots (PD-CNDs) achieved via a facile one-pot hydrothermal method. Adequate characterization using X-ray diffraction and spectroscopic and microscopic studies confirmed spherical particles with an average particle size of 2.8 nm, functionalised with amino, carboxyl, and hydroxyl groups. The carbon framework was functionalised with pyridinic and pyrrolic nitrogens. Upon 365 nm UV light illumination, an aqueous dispersion of PD-CNDs showed red-orange fluorescence. Detailed spectral analysis using UV-visible absorption and fluorescence spectroscopy identified edge states and surface groups as luminescent centres, with a significant contribution arising from the latter. The investigation conducted using a collection of solvents, categorized into polar and nonpolar, indicated the potential of the system for applications based on its solvatochromic nature. The feature enabled the determination of different polarity parameters of the solvents, as well as dielectric constants of solvents and solvent mixtures, with considerable accuracy. The system was potent for predicting the composition of a given pair of solvents. The service of the system is also extended for moisture sensing in organic solvents within an error percentage < 1. High quantum yield values (0.61) combined with solvent composition-dependent optical features ensure broader applications of the system to probe solvent interactions.

Regulating the proximity effect of heterocycle-containing AIEgens

Proximity effect, which refers to the low-lying (n,π*) and (π,π*) states with close energy levels, usually plays a negative role in the luminescent behaviors of heterocyclic luminogens. However, no systematic study attempts to reveal and manipulate proximity effect on luminescent properties. Here, we report a series of methylquinoxaline derivatives with different electron-donating groups, which show different photophysical properties and aggregation-induced emission behaviors. Experimental results and theoretical calculation reveal the gradually changed energy levels and different coupling effects of the closely related (n,π*) and (π,π*) states, which intrinsically regulate proximity effect and aggregation-induced emission behaviors of these luminogens. With the intrinsic nature of heterocycle-containing compounds, they are utilized for sensors and information encryption with dynamic responses to acid/base stimuli. This work reveals both positive and negative impacts of proximity effect in heterocyclic aggregation-induced emission systems and provides a perspective to develop functional and responsive luminogens with aggregation-induced emission properties.

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.

Multi-stimuli-responsive molecular fluorescent probes for bioapplications

Stimuli-responsive fluorescent probes have been widely utilized in detecting the physiological and pathological states of living systems. Numerous stimuli-responsive fluorescent probes have been developed due to their advantages of good sensitivity, high resolution, and high contrast fluorescent signals. In this feature article, the progress of multi-stimuli-responsive probes, including organic molecules and metal complexes, for the detection of various biomarkers for bio-applications is summarized. The feature article focuses on the applications of organic-molecule- and metal-complex-based molecular probes in biological systems for detecting different biomarkers of cancer or other diseases. The current challenges and potential future directions of these probes for applications in biological systems are also discussed.

Unexpected synthesis, delayed emission and solid-state acidochromism of novel 2,7-naphthyridine derivatives obtained from 2-(3,5-diaryl-4H-pyran-4-ylidene)malononitrile

Two novel 2,7-naphthyridine derivatives are unexpectedly synthesized by the reaction of 2-(3,5-diaryl-4H-pyran-4-ylidene)malononitrile and benzylamine, and are achieved through different ring-closing mechanisms. These two derivatives with twisted molecular conformations display phosphorescence, thermally activated delayed fluorescence, and high contrast solid-state acidochromism due to special chemical structures.

A Self-Reporting Fluorescent Salicylaldehyde-Chlorambucil Conjugate as a Type-II ICD Inducer for Cancer Vaccines

Immunogenic cell death (ICD) can activate the anticancer immune response and is highly attractive to improve cancer treatment efficacy. ICD is closely related to endoplasmic reticulum (ER) stress, and a series of ICD inducers has recently been reported based on ER-targeted photodynamic/photothermal agents or metal complexes. However, these ER-targeted ICD inducers suffer from complicated synthesis and heavy-metal cytotoxicity. Inspired by the promising clinical potential of small organic molecules, herein, an ER-targeted fluorescent self-reporting ICD inducer, SA-Cbl, is developed by simple conjugation of the chemotherapeutic drug chlorambucil (Cbl) with salicylaldehyde (SA). SA-Cbl can selectively accumulate in the ER to induce rapid ROS generation and an unfolded protein response process, which leads to a fast release of damage-associated molecular patterns and efficient dendritic cells maturation. Meanwhile, the ER-targeted accumulation and ER-stress-inducing process can be in situ monitored based on the turn-on fluorescence of SA-Cbl, which is highly pH- and polarity-sensitive and can selectively interact with ER proteins. Compared with the traditional chemotherapy drug doxorubicin, the superior anticancer immunity effect of SA-Cbl is verified via an in vivo tumor model. This study thus provides a new strategy for developing fluorescent self-reporting ICD inducers by decoration of chemotherapeutic drugs with pH and polarity-sensitive organic fluorophores.

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.

Adjusting and visualizing the stability of an acyl chloride through the delocalization effect and introducing AIEgens

Acyl chloride is an important functional group in acylation reactions, though its compounds are difficult to store and transport due to their high reactivity. In this research, phenanthro[9,10-d]imidazole is introduced into an acyl chloride agent of TPEPCl to enhance the stability via the delocalization effect. Meanwhile, rarely reported acyl chloride crystals have been achieved which could further prove its stability. The tetraphenylethylene group is also employed to visually monitor the changes of TPEPCl via fluorescent variation with the help of aggregation-induced emission (AIE) characteristics. The reactivity of TPEPCl could be stimulated by a strong alkaline solution or high temperature. Crystallography analyses of acyl TPE-PI derivatives are also discussed and the relationship between the delocalization structure and stability is determined. These findings help to stabilize, control and monitor the reactivities of active functional materials for applications.

Fluorescent In Situ 3D Visualization of Dynamic Corrosion Processes of Magnesium Alloys

Magnesium (Mg) alloys as implant materials with excellent biodegradation ability have promising clinical applications for tissue repair and restoration. Although the corrosion processes of Mg alloys in biophysiological media are closely related with their biodegradation ability, only limited methods have been developed for characterization of their corrosion processes, including electrochemical analysis, weight loss measurement, and hydrogen evolution analysis. Moreover, these methods suffer from drawbacks of poor spatiotemporal resolution, static observation, and tedious operation. To tackle these challenges, we herein developed a fluorescent probe PSPA for in situ 3D monitoring of the dynamic corrosion processes of Mg alloys on the basis of its selective turn-on detection ability toward magnesium hydroxide [Mg(OH)₂], which is the main corrosion product of Mg alloys in biophysiological media. As far as we know, this is the first example of a fluorescent probe for the monitoring of corrosion processes of Mg alloys in biophysiological media. We believe this fluorescence analysis method with easy operation and high spatiotemporal resolution advantages will contribute greatly to the clinical applications of Mg alloy implants.

Ratiometric Monitoring of Biogenic Amines by a Simple Ammonia-Response Aiegen

Herein, we developed a paper-based smart sensing chip for the real-time, visual, and non-destructive monitoring of food freshness using a ratiometric aggregation-induced emission (AIE) luminogen (i.e., H+MQ, protonated 4-(triphenylamine)styryl)quinoxalin-2(1H)-one) as pH sensitive indicators. Upon exposure to amine vapors, the deprotonation of H+MQ occurs and triggers its color change from blue to yellow, with the fluorescence redshift from blue to amaranth. Consequently, we successfully achieved the sensitive detection of ammonia vapors by recording the bimodal color and fluorescence changes. Given the high sensitivity of H+MQ to ammonia vapor, a paper-based smart sensor chip was prepared by depositing H+MQ on the commercial qualitative filter paper through a physical deposition strategy. After being placed inside the sealed containers, the developed H+MQ-loaded paper chip was applied to the real-time monitoring of biogenic amine contents according to its color difference and ratio fluorescence change. The detection results were further compared with those obtained by the high-performance liquid chromatography method, which verified the feasibility of the designed paper chip for the food spoilage degree evaluation. Briefly, this work indicates that the designed H+MQ-loaded paper chip could be a promising approach for improving food freshness monitoring.

Progress on Exploring the Luminescent Properties of Organic Molecular Aggregates by Multiscale Modeling

Luminescent molecular aggregates have attracted worldwide attention because of their potential applications in many fields. The luminescent properties of organic aggregates are complicated and highly morphology-dependent, unraveling the intrinsic mechanism behind is urgent. This review summarizes recent works on investigating the structure-property relationships of organic molecular aggregates at different environments, including crystal, cocrystal, amorphous aggregate, and doped systems by multiscale modeling protocol. We aim to explore the influence of intermolecular non-covalent interactions on molecular packing and their photophysical properties and then pave the effective way to design, synthesize, and develop advanced organic luminescent materials.

A Bioinspired Adhesive-Integrated-Agent Strategy for Constructing Robust Gas-Sensing Arrays

Gas sensors based on organic molecules are attractive for their tailored molecular structures and controllable functions, but weak interfacial adhesion between sensing materials and supporting substrates has severely hampered their practical applications, particularly in harsh environments. Here, inspired by the combined anchoring-recognizing feature of natural olfactory systems, an adhesive-integrated-agent strategy to integrate the adhesive unit (poly(dimethylsiloxane)) with the sensing unit (organoplatinum(II)) into one chemistry entity, creating robust and sensitive nanobelt array gas sensors is demonstrated. Systematic theoretical and experimental studies reveal that incorporating adhesive units significantly enhances the interfacial adhesion of the array sensors and gas-bridged super-exchange electronic couplings of sensing units ensure their efficient gas-sensing performance. The high shear strength of ≈7.05 × 10⁶ N m^-2 allows these arrays to resist aggressive ultrasonication, tape peeling, or repeated bending without compromising their sensing performance. This molecular engineering strategy opens a new guideline to develop robust gas sensors.

Amphiphilic Asymmetric Diblock Copolymer with pH-Responsive Fluorescent Properties

Stimuli-responsive polymers with changeable fluorescent properties have numerous applications in sensing, bioimaging, and detection. Here we describe the facile synthesis of a pH-responsive amphiphilic asymmetric diblock copolymer of acrylic acid and butyl acrylate that incorporates a polarity-sensitive fluorophore. The asymmetric structure enhances the stimuli-responsive behavior: as the environmental pH decreases, the fluorescent intensity of the asymmetric diblock copolymer gradually increases, whereas its symmetric block counterpart shows limited and stepwise change. Besides, this remarkable difference was demonstrated to be concentration-independent, as similar emission behavior was found for both polymers at lower concentrations. These results indicate that the fluorescence properties of the copolymer can be adjusted by rationally designing the copolymer structure. This work provides a novel and general strategy for the design and synthesis of polymeric materials with encapsulated structures showing stimuli-responsive fluorescent properties to be applied as fluorescent probes with a smoothly varying response curve rather than the simple on-off switch that is typical of block copolymer systems.

Stimuli-Responsive AIEgens

The unique advantages and the exciting application prospects of AIEgens have triggered booming developments in this area in recent years. Among them, stimuli-responsive AIEgens have received particular attention and impressive progress, and they have been demonstrated to show tremendous potential in many fields from physical chemistry to materials science and to biology and medicine. Here, the recent achievements of stimuli-responsive AIEgens in terms of seven most representative types of stimuli including force, light, polarity, temperature, electricity, ion, and pH, are summarized. Based on typical examples, it is illustrated how each type of systems realize the desired stimuli-responsive performance for various applications. The key work principles behind them are ultimately deciphered and figured out to offer new insights and guidelines for the design and engineering of the next-generation stimuli-responsive luminescent materials for more broad applications.

How to Manipulate Through-Space Conjugation and Clusteroluminescence of Simple AIEgens with Isolated Phenyl Rings

Apart from the traditional through-bond conjugation (TBC), through-space conjugation (TSC) is gradually proved as another important interaction in photophysical processes, especially for the recent observation of clusteroluminescence from nonconjugated molecules. However, unlike TBC in conjugated chromophores, it is still challenging to manipulate TSC and clusteroluminescence. Herein, simple and nonconjugated triphenylmethane (TPM) and its derivatives with electron-donating and electron-withdrawing groups were synthesized, and their photophysical properties were systematically studied. TPM was characterized with visible clusteroluminescence due to the intramolecular TSC. Experimental and theoretical results showed that the introduction of electron-donating groups into TPM could red-shift the wavelength and increase the efficiency of clusteroluminescence simultaneously, due to the increased electronic density and stabilization of TSC. However, TPM derivatives with electron-withdrawing groups showed inefficient or even quenched clusteroluminescence caused by the vigorous excited-state intramolecular motion and intermolecular photoinduced electron transfer process. This work provides a reliable strategy to manipulate TSC and clusteroluminescence.