Molecular-level enhanced clusterization-triggered emission of nonconventional luminophores in dilute aqueous solution

Multifunctional natural starch-based hydrogels: Critical characteristics, formation mechanisms, various applications, future perspectives

With the growth of the global population and increasing concern for environmental issues, the development of sustainable and eco-friendly materials has become increasingly important. Starch, as a renewable resource, is one of the most abundant polysaccharides in nature, with the advantages of good biocompatibility, high biodegradability, and low cost. Starch-based hydrogels (SBHs) have attracted widespread attention due to their unique physical and chemical properties. This article provides a comprehensive review of the latest research progress in SBHs, discussing their main characteristics, formation mechanisms, diverse applications, and future development trends. First, it outlines the biocompatibility, degradability, water absorption and retention, environmental responsiveness, and mechanical strength of SBHs. Then, it elaborates in detail on the formation mechanisms of SBHs, including physical crosslinking (hydrogen bonding, electrostatic interactions, host-guest and coordination interactions), chemical crosslinking (such as initiators, heat, light, radiation, and click reactions), and synergistic effects. Subsequently, it analyzes the applications of SBHs in cutting-edge fields such as flexible sensors, medical dressings, drug delivery, tissue engineering, soil protection, wastewater treatment, and food packaging. Finally, it summarizes the challenges in current research and provides an outlook on future development trends, emphasizing the importance of further optimizing the performance of SBHs to meet broader industrial needs and environmental protection goals. This review not only provides a systematic theoretical framework for the study of SBHs but also charts a course for their innovative applications in the field of sustainable materials, playing a significant role in advancing the continuous development of this area.

Clusteroluminescence from Random Aggregation of Micrometers to Ordered Assembly of Sub-10 Nanometers by Space-Confined Template Synthesis

Clusteroluminescence (CL) clusters in the absence of aromatic or π-conjugated structures have emerged as a new family of luminescent materials due to their abundant sources and inherent biocompatibility. However, there is an inborn challenge in controlling the size of CL clusters from random aggregation of micrometers to ordered assembly of sub-10 nanometers. Such an inherent drawback significantly restricts their progress from theoretical research to practical applications. To address this obstacle, a novel approach using space-confined templates is proposed to synthesize CL clusters with tunable sizes. Space-confined templates with sizes of ≈2-6 nm are constructed to effectively confine non-aromatic molecules, yielding size-controllable and luminescence-tunable CL clusters. The versatility of this synthetic strategy is further proved by using non-conjugated molecules, such as L-valine and L-isoleucine. Finally, the potential applications of the synthesized CL clusters have been implemented in cell nucleus imaging owing to their sub-10 nm size and efficient luminescence. The success of this work not only offers a versatile space-confined approach to synthesize size-tunable CL clusters within sub-10 nm, but also opens new avenues for the deployment of CL clusters in advanced applications.

Against the Wallach's Rule Through Rational Design of Metal-Free Chiral Perovskites Toward Efficient Red Circularly Polarized Phosphorescence

The potential applications of circularly polarized phosphorescent materials in chiroptical devices have attracted considerable interest. Nevertheless, the design of efficient near-infrared/red circularly polarized phosphorescent pure organic materials remains a significant challenge, largely due to the limitations imposed by the energy-gap law and Wallach's rule. In this study, the chiral metal-free perovskite strategy is employed to overcome these restrictions. The introduction of cyclohexylenediammonium cations as the A-site of chiral metal-free perovskites results in the generation of an efficient near-infrared/red phosphorescence at 637 nm with a lifetime of up to 227.98 µs. Furthermore, the photoluminescence quantum yield (PLQY) can reach up to 71.22%, accompanied by an anisotropy factor of 9.8 × 10-3. The figure of merit (FM = PLQY× |glum|) is 6.98 × 10-3, which is the highest value achieved among all the pure organic circularly polarized phosphorescent materials. The work proposes a unique strategy to achieve highly efficient near-infrared/red circularly polarized phosphorescence based on non-conjugated luminophores, which is accomplished by combining the superior optical and electronic properties of metal-free perovskites with chirality based on the rational molecular design.

General and Versatile Nanoarchitectonics for Amino Acid-Based Glasses via Co-Assembly of Organic Counterions

Amino acid-based biomolecular glasses represent an emerging material to meet the demand for sustainable development. However, most amino acids are difficult to vitrify due to their strong crystallization tendency, limiting further advancements of this field. In this study, we demonstrate that the introduction of counterions effectively suppresses crystallization, as hydrogen bonds within the system stabilize the disordered structures. Based on this, we propose a counterion co-assembly strategy to synthesize a wide range of amino acid-based glasses. This strategy enables the facile fabrication of glass with customizable shapes, high mechanical rigidity, and tunable multicolor fluorescence, ranging from blue to red depending on the excitation wavelength. Furthermore, this strategy allows the integration and enhancement of counterion properties within the glass matrix. Through the co-assembly of phosphorescent counterions, we synthesized a series of long-persistent luminescent glasses with significantly extended afterglow lifetimes. This work presents an effective approach for the synthesis of amino acid-based glasses and provides insights into the development of supramolecular glasses with tailored functionalities.

Bioinspired Composite Materials with Amplified Clusteroluminescence: Chemodosimetric Interaction Targeting Hypochlorite in Aqueous Medium

Owing to the advantages of cellulose such as exceptional biocompatibility and biodegradability, we synthesized cellulose-grafted bisindolyl methane (BIM) (1. Cell) composite. This biobased smart material was used as an effective colorimetric and fluorescent sensor for hypochlorite in the aqueous medium with a detection limit of 0.02 μM. Interestingly, cellulose exhibited inherent clusteroluminescence in solution, which was further intensified by the probe acting as a dopant. Both the boronic acid and bisindole groups in probe 1 are essential for this enhanced fluorescence, as boronic acid enables boronate ester formation with cellulose, while the bisindole groups facilitate additional hydrogen bonding interactions. This unique dual functionality produces a strong, solution-phase clusteroluminescent effect, creating a rigid microenvironment that promotes long-range exciton migration and an amplified fluorescence response. Furthermore, the 1. Cell exhibited ∼2.8-fold quenching, while probe 1 alone exhibited negligible fluorescence change in the presence of hypochlorite. Mechanistic investigation reveals that the probe formed a boronate ester via the interaction with cellulose, which was subsequently cleaved in the presence of hypochlorite. The differences in the response might be attributed to the distinct nature of their self-assemblies; 1. Cell could form long-range highly ordered aggregates, while probe 1 alone in the aqueous medium resulted in spontaneous random aggregates. Additionally, we employed cellulose paper strips to explore the practicability of the probe as a paper-based sensor. The chemically modified paper strips, grafted with probe molecules, were found to be stable for a week and could effectively detect hypochlorite in the presence of interfering analytes via the naked eye and fluorescent color-changing response.

Tunable Cluster Luminescence and High Quantum Yield in Amine-Modified Maleic Anhydride Polymers

Cluster luminescent materials (CLgens) with nonconjugated structures have attracted considerable attention. However, their low quantum yield and limited emission wavelengths, which are confined to the blue-green spectrum, continue to restrict their applicability. In this study, maleic anhydride polymer chains were modified with N-tristyrylene-1,2-diamine (TPM-NH2), creating a secondary donor-acceptor structure through freely rotatable phenyl groups and amino-anhydride interactions. This modification facilitated the formation of charge transfer (CT) states and strengthened the through-space interaction (TSI), resulting in a remarkable red shift in emission wavelength from 400 to 640 nm. The flexible ethyl chain acted as a bridging unit within this framework, enhancing through-space charge transfer (TSCT) and elevating the quantum yield (QY) to 28.28%. This research offers a strategy for improving the QY of anhydride copolymers and demonstrates the potential for controllable emission wavelengths, thereby broadening their application domains, including in light-conversion agricultural films.

Intrinsic Multicolor Emissive Aliphatic Linear Polyphosphate Esters From the Charge-Transfer-Induced Enhanced Spatial Electronic Communication

Unconventional fluorescent polymers are attracting increasing attention because of their excellent biocompatibility and wide applications. However, these polymers typically exhibit weak long-wavelength emission. Herein, three novel aliphatic linear polyphosphate esters are prepared via a one-pot polycondensation reaction. Such polymers can generate strong blue, green, yellow, and red fluorescence under different excitations. Experimental and theoretical results showed that the cluster of C═C and phosphate ester groups attracted the negative charge of isolated functional groups, and the alkane chains and hydrogen atoms also provided a negative charge for spatial electronic communication. Then, intrinsic fluorescence arises from the charge-transfer-induced enhanced spatial electronic communication. Additionally, these polymers show potential applications in fluorescence film, ion detection, bacteria imaging, and visualization of the NaCl crystallization process. This work provides a universal design strategy for developing strong long-wavelength emissive polymers and gains new insight into intrinsic emission mechanisms.

Nonconventional Fluorescent Non-Isocyanate Polyurethane Foams for Multipurpose Sensing Applications

Fluorescent foams with interconnected pores are attractive for the detection and quantification of various products. However, many fluorescent probes are suffering from aggregation-caused fluorescence quenching in their solid/aggregated state, are costly, and/or not straightforward to incorporate in foams, limiting their utility for this application. Herein, non-isocyanate polyurethane foams, prepared by the simple water-induced self-blowing process, present a nonconventional fluorescence behaviour, i.e. they are intrinsically fluorescent with a multicolor emission without requiring ex situ traditional fluorescent probes. These foams demonstrate utility for capturing-sensing gaseous formaldehyde (an emblematic indoor air pollutant), as well as for detecting and quantifying various metal ions (Fe2+, Cu2+, Fe3+, Hg2+). They are also able to selectively sense tetracycline antibiotic in a ratiometric way with a high sensitivity. By exploiting the unique multicolor photoluminescent foam properties, a smartphone-compatible device is used for the facile antibiotic quantification. This nonconventional fluorescence behaviour is discussed experimentally and theoretically, and is mainly based on clusteroluminescence originating from multiple hydrogen bonding and hetero-atomic sub-luminophores, thus from aggregation-induced emission luminogens that are naturally present in the foams. This work illustrates that easily accessible non-conventional fluorescent NIPU foams characterized by a modular emission wavelength have an enormous potential for multiple substrates detection and quantification.

π-π conjugated PDI supramolecular regulating the photoluminescence of imine-COFs for sensitive smartphone visual detection of levofloxacin

As the contamination and enrichment in food chain of levofloxacin (LV) antibiotics have caused a significant threat to life safety, the instant detection of LV has become an urgent need. Here, a PDI-functionalized imine-based covalent organic framework (PDI-COF300) was prepared by the electrostatic self-assembly method as fluorescent probe for smartphone visual detection of LV, which exhibited excellent fluorescence quantum yield (82.68%), greater stability, high sensitivity with detection limit of 0.303 μM. Based on the results of molecular docking and Stern-Volmer equation, the LV detection by PDI-COF300 was mainly a static quenching process through π-π stacked hydrophobic interactions and fluorescence resonance energy transfer. Besides, PDI-COF300 was applied to LV detection in environmental medium and milk samples with recoveries from 85.56% to 108.34% and relative standard deviations <2.70%. This work also provided a new general strategy for using PDI-COF in smartphone devices and fluorescent papers for LV fluorescence detection and microanalysis.

Odd-Even Law Mediated Supramolecular Chirality of Luminescent Dipeptides for Chiroptical Energy Transfer

Inherent luminescent short peptides essentially provide opportunities to rationally manipulate supramolecular chirality and chiral luminescence. Herein, a facile protocol to construct a series of naphthalimide-appended dipeptides is reported that show ultrasound wave-activated supramolecular chirality regulated by odd-even law. Naphthalimide luminophores are conjugated to the dipeptide skeleton with variable alkyl spacers. The presence of tyrosine interferes the kinetic aggregation into achiral nanoparticles without chirality transfer to supramolecular scale. However, ultrasound treatment initiates the nanoparticle-to-helix transition accompanied with the appeared chiral optics, including Cotton effect and circularly polarized luminescence (CPL). The supramolecular chiral parameters, including handedness of helices and chiroptical behaviors, follow the odd-even law of alkyl spacers in dipeptides bearing non-substituted naphthalimides. The amine-substitution boosted the quantum yields of dipeptide whereas no odd-even effect. The two types of dipeptides constituted ideal energy transfer pairs that enable the efficient energy transfer as well as the transportation of odd-even law to dipeptides containing substituted naphthalimides. This work sheds light on the construction of luminescent dipeptides with applications in precise control over chirality transportation and chiral luminescence.

Unconventional Luminescence Polymer with Color-Tunability based on Solvent-Induced Electrostatic Potential Distribution of Fluorophore

Tuning full-color emission of polymers holds significant promise. However, preparing unconventional luminescence polymers with color-tunability in dilute solution and understanding the relationship between non-covalent interactions and luminescent behavior remains a great challenge. We report two emitters (P1 and P2) incorporating tetracoordinate boron. The P1 with non-conjugated D-π-A structure, exhibited red delayed fluorescence at 645 nm with quantum yield of 9.15 % in aggregates. Notably, the emission wavelength of P1 can be tuned from 418 to 588 nm at different solvent. Similarly, the emission wavelength of P2 can also be adjusted by manipulating the interactions between the solvent and fluorophore. Experimental characterization and theoretical calculations indicate that the B←N bond and electronic interactions between solvent and fluorophore significantly regulate the equilibrium the electrostatic potential (ESP) and the intramolecular O⋅⋅⋅O interactions of P1, thereby modulating its emission wavelength. Additionally, these polymers showed excellent potential in fluoride ions detection. This work provides new insights into the complex effects of intermolecular interactions on luminescent properties.

PBI derivatives/surfactant-based fluorescent ensembles: Sensing of multiple aminoglycoside antibiotics and interaction mechanism studies

Fluorescent aggregates and ensembles have been widely applied in fabrication of fluorescent sensors due to their capacity of encapsulating fluorophores and modulating their photophysical properties. In the present work, fluorescent ensembles based on anionic surfactant SDS assemblies and perylene derivatives (PBIs) were particularly constructed. Three newly synthesized neutral PBI derivatives with different structures, PO, PC1 and PC2, were used for the purpose to evaluate probe structure influence on constructing fluorescent ensembles. The one with hydrophilic side chains, PO, experienced distinct photophysical modulation effect by SDS assemblies. The ensemble based on PO@SDS assemblies displayed effective fluorescence variation to antibiotic aminoglycosides (AGs). To improve cross-reactivity and discrimination capability of ensembles, a second probe, coumarin, was introduced into PO@SDS assemblies. The resultant ternary sensor, CM-PO@SDS, exhibited good qualitative and quantitative detection capabilities, and achieved differentiation of eight AGs and mixed AG samples both in aqueous solution and actual biological fluid, like human serum. Sensing mechanism studies revealed that hydrogen bonding, electrostatic and hydrophobic interactions are involved in the sensing process. This surfactant-based fluorescent ensemble provides a simple and feasible method for assessing AGs levels. Meanwhile, this work may provide some insights to design reasonable probes for constructing effective single-system based discriminative fluorescent amphiphilic sensors.

Stable Persistent Room-Temperature Phosphorescent Hydrogels Based on Ionically Crosslinked Nonaromatic Carboxylate Polymers

Developing pure organic room-temperature phosphorescent (RTP) hydrogels is important for expanding the practical applications of phosphorescent materials. However, most of the reported RTP hydrogels containing aromatic phosphors suffer from short phosphorescent lifetimes, unstable underwater RTP emissions, and complex preparation processes. Herein, novel nonaromatic RTP hydrogels are prepared by using two types of non-traditional luminescent polymers, sodium alginate and a polymeric carboxylate, which are not RTP emissive or very weakly emissive in aqueous environments. The prepared hydrogels exhibit the following features: I) color-tunable RTP emissions with ultra-long lifetimes up to 451.1 ms, II) excellent anti-swelling properties and stable persistent RTP emission even after being immersed in deionized water for months, III) efficient and large-scale preparation of hydrogel fibers by wet spinning technique. Experiment results and theoretical calculations show that the stable and long-lifetime RTP emissions of the hydrogels originate from the introduction of more nonconventional chromophores which are strongly crosslinked with ionic bonding between carboxylate groups and calcium ions and enhanced through-space interactions between them. This work provides a reliable strategy for designing nonaromatic hydrogels with stable and persistent RTP.

Elucidation of the photoluminescence mechanism and determination of the configuration content of arabinose isomer solution by fluorescence analysis

A fluorescence method has been successfully constructed to accurately measure the D/L-Arb configuration content in optical isomers, and its application in ion detection has been expanded, which has greater sensitivity and universality than the circular dichroism (CD) method. It also promotes the study of the emission mechanism of nonconventional luminogens.

Cyclodextrin supramolecular assembly confined luminescent materials

The macrocyclic supramolecular assembly confinement effect not only induces or extends the fluorescence/phosphorescence luminescence behavior of guest molecules but has also been widely applied in the research fields of chemistry, biology, and materials. This review primarily describes recent advances in cyclodextrin (CD) supramolecular assembly confined luminescent materials. Taking advantage of their hydrophobic cavity, CDs and their derivatives effectively encapsulate guest molecules and special functional groups or further assemble and polymerize to restrict the motion of guest chromophores, inducing and enhancing the luminescence behavior and realizing intelligent stimulus-responsive luminescence depending on changes in temperature, light, redox reactions and solvent polarity, which are successfully applied in targeted cell imaging, sensing, information encryption, anti-counterfeiting and flexible electronic light-emitting devices. With the emergence of new chromophores and CD primitives, spatial confinement within CD supramolecular assemblies will further realize the rapid development of supramolecular science and technology in circularly polarized luminescence, fluorescence/phosphorescence cascade energy transfer, light-harvesting energy-transfer systems and long persistent luminescent materials.

Monitoring Binding of Protamine with DNA Using Protein Charge Transfer Spectra

In this work, novel intrinsic electronic absorption (250-400 nm) with a molar extinction coefficient of 752 M-1cm-1 at 250 nm, arising from photoinduced electron transfer involving charged amino acid side chains and the polypeptide backbone, along with luminescence (300-500 nm) with quantum yield of 0.011 from subsequent charge recombination, was observed in salmon sperm Protamine (PRM). The absorption of PRM was attributed to the previously identified Peptide Backbone-to-Side chain Charge Transfer (PBS-CT) from the polypeptide backbone to the abundant cationic headgroups of Arginine in PRM, while the luminescence was believed to originate from charge recombination within the charge-separated excited states of PRM. Remarkably, since Arg is the only charged residue in the PRM sequence, the PRM Protein Charge Transfer Spectra (ProCharTS) is both totally and uniquely Arg specific. Interestingly, the peak of PRM luminescence emission spectrum was independent of the excitation wavelength, unlike other proteins such as human serum albumin, displaying unconventional luminescence. Aggregation-induced effects on PRM absorbance and luminescence were ruled out, as both PRM absorbance and luminescence increase maintained linearity with increasing concentration in the 25-150 μM range. Nucleoprotamine complex formation, resulting from the binding of PRM with calf-thymus genomic DNA (gDNA), was monitored through increased scattering by the nucleoprotamine complex, a decrease in gDNA/PRM absorbance, a decrease in gDNA/PRM ellipticity, and shifts of nucleoprotamine complex band upon agarose gel electrophoresis. Upon binding with gDNA (700 μM base pair concentration), PRM ProCharTS absorbance at 260 nm decreased by 72%. This decrease was attributed to the formation and subsequent precipitation of nucleoprotamine complex upon PRM-gDNA binding. The application of ProCharTS absorbance to indirectly monitor DNA-protein binding in a label-free approach was thus demonstrated.

Lysine-mediated surface modification of cellulose nanocrystal films for multi-channel anti-counterfeiting

Utilizing advanced multiple channels for information encryption offers a powerful strategy to achieve high-capacity and highly secure data protection. Cellulose nanocrystals (CNCs) offer a sustainable resource for developing information protection materials. In this study, we present an approach that is easy to implement and adapt for the covalent attachment of various fluorescence molecules onto the surface of CNCs using the Mannich reaction in aqueous-based medium. Through the use of the Mannich reaction-based surface modification technique, we successfully achieved multi-color fluorescence in the resulting CNCs. The resulting CNC derivatives were thoroughly characterized by two dimensional heteronuclear single quantum coherence nuclear magnetic resonance (2D HSQC NMR) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron (XPS) spectroscopy. Notably, the optical properties of CNCs were well maintained after modification, resulting in films exhibiting blue and red structural colors. This enables the engineering of highly programmable and securely encoded anti-counterfeit labels. Moreover, subsequent coating of the modified CNCs with MXene yielded a highly secure encrypted matrix, offering advanced security and encryption capabilities under ultraviolet, visible, and near-infrared wavelengths. This CNC surface-modification enables the development of multimodal security labels with potential applications across various practical scenarios.

Research progress of fluorescent composites based on cyclodextrins: Preparation strategies, fluorescence properties and applications in sensing and bioimaging

Fluorescence analysis has been regarded as one of the commonly used analytical methods because of its advantages of simple operation, fast response, low cost and high sensitivity. So far, various fluorescent probes, with noble metal nanoclusters, quantum dots, organic dyes and metal organic frameworks as representatives, have been widely reported. However, single fluorescent probe often suffers from some deficiencies, such as low quantum yield, poor chemical stability, low water solubility and toxicity. To overcome these disadvantages, the introduction of cyclodextrins into fluorescent probes has become a fascinating approach. This review (with 218 references) systematically covers the research progress of fluorescent composites based on cyclodextrins in recent years. Preparation strategies, fluorescence properties, response mechanisms and applications in sensing (ions, organic pollutants, bio-related molecules, temperature, pH) and bioimaging of fluorescent composites based on cyclodextrins are summarized in detail. Finally, the current challenges and future perspectives of these composites in relative research fields are discussed.

Design and evaluation of fluorescent chitosan-starch hydrogel for drug delivery and sensing applications

Composite bio-based hydrogels have been obtaining a significant attention in recent years as one of the most promising drug delivery systems. In the present study, the preparation of composite chitosan-starch hydrogel using maleic acid as a cross-linker was optimized with the help of response surface methodology. The synthesized hydrogel was fluorescent owing to clustering of large number of functional groups. Different analytical techniques, including XRD, FTIR, SEM, XPS, fluorescence and BET were utilized to characterize the prepared hydrogel. XRD analysis confirmed the formation of non-crystalline hydrogel with random arrangement of macromolecular chains. The composite hydrogel exhibited good swelling percentage with pH sensitivity, hemocompatibility and degradability. BET analysis confirmed that the variation in concentration of crosslinker significantly influences the pore volume of the hydrogel. The synthesized composite chitosan-starch hydrogel was utilized as a prospective candidate for controlling drug release. Cefixime as a model drug was loaded onto the synthesized hydrogel utilizing the swelling diffusion method. SEM micrographs showed uniform distribution of drug molecules in the drug loaded hydrogel. In vitro drug release experiments indicated the swelling dependent drug release behaviour of chitosan-starch hydrogel with higher drug release at pH 7.4 (93.08 %) compared to pH 1.2 (67.85 %). The composite chitosan-starch hydrogel was able to prolong and control the drug release up to 12 h. The drug release from the hydrogel followed Korsmeyer-Peppas and Makoid-Banakar model with Fickian diffusion mechanism. Further, the composite hydrogel displayed excitation dependent fluorescence emission with most intense blue emission band at 425 nm with an excitation wavelength of 350 nm. The inclusion of cefixime drug in the hydrogel matrix significantly reduced the fluorescence intensity; the decrease was linearly correlated to the concentration of the drug. Moreover, the fluorescence emission the chitosan-starch hydrogel was found to be dependent upon pH. The synthesized hydrogel is expected to be a potential candidate for controlled drug release as well as for fluorescent sensing applications.

Clustering-triggered emission mechanism of carboxymethyl β-cyclodextrin aqueous solution and efficient recognition of Fe3+ in mixed ions

Most nonconventional luminogens enjoy good water solubility and biocompatibility, showing unique application prospects in fields like biological imaging. Although clustering-triggered emission (CTE) mechanisms have been proposed to explain such emissions, the have not been thoroughly elucidated, which limits their development and application. Here, the photoluminescence properties of carboxymethyl β-cyclodextrin (CM-β-CD) aqueous solution are utilized to further investigate the effects of changes in concentration, in order to elucidate the emission mechanism through cryo-transmission electron microscopy (cryo-TEM), small-angle X-ray scattering (SAXS), molecular interaction analysis, and theoretical calculation. The results showed that the size distribution, morphology, and distance between water aggregates were successfully correlated with the cluster emission centers. The emission mechanism of nonconventional luminogen solutions was more clearly and intuitively elucidated, which has a promoting effect on the emission and application of this field. It is interesting that temperature-dependent emission spectra show the blue-shift phenomenon of PL with increasing excitation wavelengths. Moreover, due to its strong static quenching effect for Fe3+, CM-β-CD can efficiently detect Fe3+ in mixed-ion aqueous solutions. It provides a strategy to clarify the CTE mechanism of nonconventional luminogen solutions more clearly and its application of mixed-ion detection.

Narrowband clusteroluminescence with 100% quantum yield enabled by through-space conjugation of asymmetric conformation

Different from traditional organic luminescent materials based on covalent delocalization, clusteroluminescence from nonconjugated luminogens relies on noncovalent through-space conjugation of electrons. However, such spatial electron delocalization is usually weak, resulting in low luminescent efficiency and board emission peak due to multiple vibrational energy levels. Herein, several nonconjugated luminogens are constructed by employing biphenyl as the building unit to reveal the structure-property relationship and solve current challenges. The intramolecular through-space conjugation can be gradually strengthened by introducing building units and stabilized by rigid molecular skeleton and multiple intermolecular interactions. Surprisingly, narrowband clusteroluminescence with full width at half-maximum of 40 nm and 100% efficiency is successfully achieved via an asymmetric conformation, exhibiting comparable performance to the traditional conjugated luminogens. This work realizes highly efficient and narrowband clusteroluminescence from nonconjugated luminogens and highlights the essential role of structural conformation in manipulating the photophysical properties of unconventional luminescent materials.

Harvesting Multicolor Photoluminescence in Nonaromatic Interpenetrated Metal-Organic Framework Nanocrystals via Pressure-Modulated Carbonyls Aggregation

Interpenetrated metal-organic frameworks (MOFs) with nonaromatic ligands provide a unique platform for adsorption, catalysis, and sensing applications. However, nonemission and the lack of optical property tailoring make it challenging to fabricate smart responsive devices with nonaromatic interpenetrated MOFs based on ligand-centered emission. In this paper, the pressure-induced aggregation effect is introduced in nonaromatic interpenetrated Zn4O(ADC)4(Et3N)6 (IRMOF-0) nanocrystals (NCs), where carbonyl groups aggregation results in O─O distances smaller than the sum of the van der Waals radii (3.04 Å), triggering the photoluminescence turn-on behavior. It is noteworthy that the IRMOF-0 NCs display an ultrabroad emission tunability of 130 nm from deep blue (440 nm) to yellow (570 nm) upon release to ambient conditions at different pressures. The eventual retention of through-space n-π* interactions in different degrees via pressure treatment is primarily responsible for achieving a controllable multicolor emission behavior in initially nonemissive IRMOF-0 NCs. The fabricated multicolor phosphor-converted light-emitting diodes based on the pressure-treated IRMOF-0 NCs exhibit excellent thermal, chromaticity, and fatigue stability. The proposed strategy not only imparts new vitality to nonaromatic interpenetrated MOFs but also offers new perspectives for advancements in the field of multicolor displays and daylight illumination.

Recent Progress in Nonconventional Luminescent Macromolecules and their Applications

Traditional π-conjugated luminescent macromolecules typically suffer from aggregation-caused quenching (ACQ) and high cytotoxicity, and they require complex synthetic processes. In contrast, nonconventional luminescent macromolecules (NCLMs) with nonconjugated structures possess excellent biocompatibility, ease of preparation, unique luminescence behavior, and emerging applications in optoelectronics, biology, and medicine. NCLMs are currently believed to produce inherent luminescence due to through-space conjugation of overlapping electron orbitals in solid/aggregate states. However, as experimental facts continue to exceed expectations or even overturn some previous assumptions, there is still controversy about the detailed luminous mechanism of NCLMs, and extensive studies are needed to further explore the mechanism. This Perspective highlights recent progress in NCLMs and classifies and summarizes these advances from the viewpoint of molecular design, mechanism exploration, applications, and challenges and prospects. The aim is to provide guidance and inspiration for the huge fundamental and practical potential of NCLMs.

Synthesis of highly luminescent core-shell nanoprobes in a single pot for ofloxacin detection in blood serum and water

Antibiotics are commonly used as antibacterial medications due to their extensive and potent therapeutic properties. However, the overconsumption of these chemicals leads to their accumulation in the human body via the food chain, amplifying drug resistance and compromising immunity, thus presenting a significant hazard to human health. Antibiotics are classified as organic pollutants. Therefore, it is crucial to conduct research on precise methodologies for detecting antibiotics in many substances, including food, pharmaceutical waste, and biological samples like serum and urine. The methodology described in this research paper introduces an innovative technique for producing nanoparticles using silica as the shell material, iron oxide as the core material, and carbon as the shell dopant. By integrating a carbon-doped silica shell, this substance acquires exceptional fluorescence characteristics and a substantial quantum yield value of 80%. By capitalising on this characteristic of the substance, we have effectively constructed a fluorescent sensor that enables accurate ofloxacin analysis, with a detection limit of 1.3 × 10-6 M and a linear range of concentrations from 0 to 120 × 10-6 M. We also evaluated the potential of CSIONPs for OLF detection in blood serum and tap water analysis. The obtained relative standard deviation values were below 3.5%. The percentage of ofloxacin recovery from blood serum ranged from 95.52% to 103.28%, and from 89.9% to 96.0% from tap water.

Photoluminescence quantum yield of carbon dots: emission due to multiple centers versus excitonic emission

Carbon dots (CDs) are recognized as promising fluorescent nanomaterials with bright emission and large variations of photoluminescence quantum yield (PLQY). However, there is still no unique approach for explanation of mechanisms and recipes for synthetic procedures/chemical composition of CDs responsible for the enhancement of PLQY. Here, we compare photophysical behavior and PLQY of two types of CDs synthesized by different routes, leading to the different extent of oxidation and composition. The first type of CDs represents a conjugated carbon system oxidized by F, N and O heteroatoms, whereas the second type represents a non-conjugated carbon system oxidized by oxygen. Photophysical data, photoemission spectroscopy and microscopy data yield the suggestion that in the first case, a structure with a distinct carbon core and highly oxidized electron-accepting shell is formed. This leads to the excitonic type non-tunable emission with single-exponent decay and high PLQY with a strong dependence on the solvent polarity, being as high as 93% in dioxane and as low as 30% in aqueous medium, but which is vulnerable to photobleaching. In the second case, the oxidized CDs do not indicate a clear core-shell structure and show poor solvatochromism, negligible photobleaching, low PLQY varying in the range of 0.7-2.3% depending on the solvent used, and tunable emission with multi-exponent decay, which can be described by the model of multiple emission centers acting through a clustering-triggered emission mechanism. The obtained results lead to a strategy that allows one to design carbon nanomaterials with principally different PLQYs that differ by orders of magnitude.

Chirality-Regulated Clusteroluminescence in Polypeptides

The low emission efficiency of clusteroluminogens restricts their practical applications in the fields of sensors and biological imaging. In this work, the clusteroluminescence of ordered/disordered polypeptides was observed, and the photoluminescence (PL) intensity of polypeptides can be modulated by the chirality of amino acid residues. Polyglutamates with different chiral compositions were synthesized, and the racemic polypeptides exhibited a significantly higher PL intensity than the enantiopure ones. This emission originates from the n-π* transition between C═O groups of polypeptides and is enhanced by clusterization of polypeptides. CD and Fourier transform infrared spectra demonstrated that the enantiopure and racemic polypeptides form α-helix and random coil structures, respectively. The disordered polypeptides can form more chain entanglements and interchain interactions because of their high flexibility, leading to more clusterizations and stronger PL intensity. The rigidity of ordered helical structures restrains the chain entanglements, and the formation of intrachain hydrogen bonds between amide groups of the backbone impairs the interchain interaction between polypeptides, resulting in lower PL intensity. The PL intensity of the polypeptides can also be manipulated by the addition of urea or trifluoroacetic acid. Our study not only elucidates the chirality/order-based structure-property relationship of clusteroluminescence in peptide-based polymers but also offers implications for the rational design of fluorescent peptides/proteins.

The Balance Effect of π-π Electronic Coupling on NIR-II Emission and Photodynamic Properties of Highly Hydrophobic Conjugated Photosensitizers

Deep NIR organic phototheranostic molecules generally have large π-conjugation structures and show highly hydrophobic properties, thus, forming strong π-π stacking in the aqueous medium, which will affect the phototheranostic performance. Herein, an end-group strategy is developed to lift the performance of NIR-II emitting photosensitizers. Extensive characterizations reveal that the hydrogen-bonding interactions of the hydroxyl end group can induce a more intense π-π electronic coupling than the chlorination-mediated intermolecular forces. The results disclose that π-π stacking will lower fluorescence quantum yield but significantly benefit the photodynamic therapy (PDT) efficiency. Accordingly, an asymmetrically substituted derivative (BTIC-δOH-2Cl) is developed, which shows balanced phototheranostic properties with excellent PDT efficiency (14.6 folds of ICG) and high NIR-II fluorescence yield (2.27%). It proves the validity of the end-group strategy on controlling the π-π interactions and rational tuning the performance of NIR-II organic phototheranostic agents.

A Self-Assemble Supramolecular Film with Humidity Visualization Enabled by Clusteroluminescence

Clusteroluminescence (CL) has recently gained significant attention due to its unique through-space interactions associated with a high dependence on the aggregation of subgroups. These distinct features could easily transform the stimuli into visual fluorescence and monitor the fluctuation of the environment but have not received sufficient attention before. In this work, supramolecular films are designed based on the neutralization reaction of anhydride groups and the self-assembly of dynamic covalent disulfide bonds in NaOH aqueous solution. The self-assembly of hydrophilic carboxylate chromophores and hydrophobic disulfide-containing five-membered rings could be observed by the variation of the aggregation state of carboxylate in CL. Furthermore, the dynamic cross-linking films obtained with water-sensitive carboxylate chromophores could alter the aggregation distance stimulated by surrounding water vapor, causing the emission wavelength to change from 534 to 508 nm by varying the relative humidity. This work not only provides an approach to monitor the self-assembly of clusteroluminogens but also offers new strategies for designing stimuli-responsive materials that utilize the intrinsic features of CL.

Hyperbranched Polyborosiloxanes: Non-traditional Luminescent Polymers with Red Delayed Fluorescence

Non-traditional fluorescent polymers have attracted significant attention for their excellent biocompatibility and diverse applications. However, designing and preparing non-traditional fluorescent polymers that simultaneously possess long emission wavelengths and long fluorescence lifetime remains challenging. In this study, a series of novel hyperbranched polyborosiloxanes (P1-P4) were synthesized. As the electron density increases on the monomer diol, the optimal emission wavelengths of the P1-P4 polymers gradually red-shift to 510, 570, 575, and 640 nm, respectively. In particular, P4 not only exhibits red emission but also demonstrates delayed fluorescence with a lifetime of 9.73 μs and the lowest critical cluster concentration (1.76 mg/mL). The experimental results and theoretical calculations revealed that the synergistic effect of dual heteroatom-induced electron delocalization and through-space O⋅⋅⋅O and O⋅⋅⋅N interaction was the key factor contributing to the red-light emission with delayed fluorescence. Additionally, these polymers showed excellent potential in dual-information encryption. This study provides a universal design strategy for the development of unconventional fluorescent polymers with both delayed fluorescence and long-wavelength emission.

Molecularly imprinted polymers-isolated AuNP-enhanced CdTe QD fluorescence sensor for selective and sensitive oxytetracycline detection in real water samples

A molecularly imprinted polymers (MIPs)-isolated AuNP-enhanced fluorescence sensor, AuNP@MIPs-CdTe QDs, was developed for highly sensitive and selective detection of oxytetracycline (OTC) in aqueous medium. The developed sensor combined the advantages of strong fluorescence signal of metal-enhanced fluorescence (MEF), high selectivity of MIPs, and stability of CdTe QDs. The MIPs shell with specific recognition served as an isolation layer to adjust the distance between AuNP and CdTe QDs to optimize the MEF system. The sensor demonstrated the detection limit as low as 5.22 nM (2.40 μg/L) for a concentration range of 0.1-3.0 μM OTC and good recovery rates of 96.0-103.0% in real water samples. In addition, high specificity recognition for OTC over its analogs was achieved with an imprinting factor of 6.10. Molecular dynamics (MD) simulation was utilized to simulate the polymerization process of MIPs and revealed H-bond formation as the mainly binding sites of APTES and OTC, and finite-difference time-domain (FDTD) analysis was employed to obtain the distribution of electromagnetic field (EM) for AuNP@MIPs-CdTe QDs. The experimental results combined with theoretical analyses not only provided a novel MIP-isolated MEF sensor with excellent detection performance for OTC but also established a theoretical basis for the development of a new generation of sensors.

Designing Nonconventional Luminescent Materials with Efficient Emission in Dilute Solutions via Modulation of Dynamic Hydrogen Bonds

Nonconventional luminescent materials (NLMs) which do not contain traditional aromatic chromophores are of great interest due to their unique chemical structures, optical properties, and their potential applications in various areas, such as cellular imaging and chemical sensing. However, most reported NLMs show weak or no emission in dilute solutions, which severely limits their applications. In this work, dynamic hydrogen bonds were utilized to design NLMs with efficient emission in dilute solutions. To further validate the results, polymers P1 and P2 were successfully prepared and investigated. It was found that the luminescence quantum efficiency of P1 and P2 at a concentration of 0.1 mg/mL in water solution was 8.9 and 0.6%, respectively. The high efficiency can be attributed to the fact that polymer P1 has more intra- or intermolecular dynamic hydrogen bonds and other short interactions than P2 in dilute solutions, allowing P1 to achieve the through-space conjugation effect to increase the degree of system conjugation, restrict molecular motion, and decrease nonradiative transitions, which can effectively improve luminescence. In addition, polymer P2 exhibits the characteristics of clustering-triggered emission, excitation wavelength-dependent and concentration-dependent fluorescence properties, excellent photobleaching resistance, low cytotoxicity, and selective recognition of Fe³⁺. The present study investigates the manipulation of luminescence properties of NLMs in dilute solutions through the modulation of dynamic hydrogen bonds. This approach can serve as a semi-empirical technique for designing and building innovative NLMs in the times ahead.