Functional 1,8-Naphthalimide AIE/AIEEgens: Recent Advances and Prospects

Fluorescent Probes for Selective Recognition of Hypobromous Acid: Achievements and Future Perspectives

Reactive oxygen species (ROS) have been implicated in numerous pathological processes and their homeostasis facilitates the dynamic balance of intracellular redox states. Among ROS, hypobromous acid (HOBr) has a high similarity to hypochlorous acid (HOCl) in both chemical and physical properties, whereas it has received relatively little attention. Meanwhile, selective recognition of endogenous HOBr suffers great challenges due to the fact that the concentration of this molecule is much lower than that of HOCl. Fluorescence-based detection systems have emerged as very important tools to monitor biomolecules in living cells and organisms owing to distinct advantages, particularly the temporal and spatial sampling for in vivo imaging applications. To date, the development of HOBr-specific fluorescent probes is still proceeding quite slowly, and the research related to this area has not been systematically summarized. In this review, we are the first to review the progress made so far in fluorescent probes for selective recognition and detection of HOBr. The molecular structures, sensing mechanisms, and their successful applications of these probes as bioimaging agents are discussed here in detail. Importantly, we hope this review will call for more attention to this rising field, and that this could stimulate new future achievements.

Design and Application of Receptor-Targeted Fluorescent Probes Based on Small Molecular Fluorescent Dyes

In recent years, a variety of receptor-targeted fluorescent probes have been developed and widely used to realize the visualization of certain receptors, which facilitates the early diagnosis and treatment of diseases. In this Review, we focus on the recent achievements in design, chemical structure, imaging characterization, and potential applications of receptor-targeted fluorescent probes from the past 10 years. The development and application of receptor-targeted fluorescent probes will expand our knowledge of the distribution and function of disease-related receptors, shed light on the drug discovery for clinical diseases where receptors are implicated, and feed into the diagnosis and treatment of a plethora of diseases, including tumors.

Fluorescent 4-amino-1,8-naphthalimide Tröger's bases (TBNaps) possessing (orthogonal) 'α-amino acids', esters and di-peptides and their solvent dependent photophysical properties

The synthesis of fifteen luminescent bis-naphthalimide based Tröger's bases (TBNaps) derived from 4-amino-1,8-naphthalimide (4-Amino-Nap) precursors is described; these scaffolds possess α-amino acids, esters or di-peptides conjugated at the imide site and show minor fluorescence in aqueous solution while being highly emissive in organic solvents. The investigation shows that these TBNaps possessing ICT excited state properties are capable of generating either positive or negative solvatochromic effects in response to changes in polarity and/or the hydrogen bonding capabilities of the medium.

Naphthalimide based fluorescent organic nanoparticles in selective sensing of Fe3+ and as a diagnostic probe for Fe2+/Fe3+ transition

Fluorescent organic nanoparticles (FONPs) have attracted considerable attention as a practical and effective platform for sensing and imaging applications. The present article delineates the fabrication of FONPs derived from the naphthalimide based histidine appended amphiphile, NID. The self-assembly of NID in 99 vol% water in DMSO led to the formation of FONPs through J-type aggregation. Aggregation-induced emission (AIE) was observed due to the pre-associated excimer of NID with bluish green emission at 470 nm along with intramolecular charge transfer (ICT). The emission of NID FONPs was utilized for selective sensing of Fe³⁺ and bioimaging of Fe³⁺ inside mammalian cells. The fluorescence intensity of the FONPs was quenched with the gradual addition of Fe³⁺ due to the formation of a 1 : 1 stoichiometric complex with the histidine residue of NID. The morphology of the FONPs transformed from spherical to spindle upon the complex formation of NID with Fe³⁺. The limit of detection (LOD) of this AIE based turn-off chemosensor for Fe³⁺ was found to be 12.5 ± 1.2 μM having high selectivity over other metal ions. On the basis of the very low cytotoxicity and selective sensing of Fe³⁺, NID FONPs were successfully employed for bioimaging of Fe³⁺ ions through fluorescence quenching within mammalian cells (NIH3T3, B16F10). Considering the varying oxidative stress inside different cells, NID FONPs were used for detecting Fe²⁺ to Fe³⁺ redox state transition selectively inside cancer cells (B16F10) in comparison to non-cancerous cells (NIH3T3). Selective sensing of cancer cells was substantiated by co-culture experiment and flow cytometry. Hence, NID FONPs can be a selective diagnostic probe for cancer cells owing to their higher H₂O₂ content.

Efficient FRET Approaches toward Copper(II) and Cyanide Detections via Host-Guest Interactions of Photo-Switchable [2]Pseudo-Rotaxane Polymers Containing Naphthalimide and Merocyanine Moieties

A supramolecular [2]pseudo-rotaxane containing a naphthalimide-based pillararene host and a spiropyran-based imidazole guest was synthesized and investigated in a semiaqueous solution with 90% water fraction. Upon UV exposure, the close-form structure of nonemissive spiropyran guest could be transformed into the open-form structure of red-emissive merocyanine guest reversibly, which was utilized as a monofluorophoric sensor to detect copper(II) and cyanide ions. Moreover, the naphthalimide host as an energy donor with green photoluminescence (PL) emission at 505 nm was complexed with the merocyanine guest as an energy acceptor with red PL emission at 650 nm in 1:1 molar ratio to generate a [2]pseudo-rotaxane polymer, which was further verified by the diffusion coefficients of DOSY nuclear magnetic resonance (NMR) measurements. Due to the Förster resonance energy transfer (FRET) processes, the bifluorophoric [2]pseudo-rotaxane produced more efficient ratiometric PL behavior to induce a stronger red PL emission than that of the monofluorophoric guest; therefore, the PL sensor responses of the supramolecular [2]pseudo-rotaxane toward copper(II) and cyanide ions could be further amplified via the FRET-OFF processes to turn off red PL emission of the reacted merocyanine acceptor and to recover green PL emission of the naphthalimide donor. Accordingly, the best and prominent values of the limit of detection (LOD) for the host-guest detections toward Cu²⁺ and CN^- were 0.53 and 1.34 μM, respectively. The highest red MC emission with the optimum FRET processes of [2]pseudo-rotaxane was maintained around room temperature (20-40 °C) in wide pH conditions (pH = 3-13), which can be utilized in the cell viability tests to prove the nontoxic and remarkable biomarker of [2]pseudo-rotaxane to detect Cu²⁺ and CN^- in living cells. The developed FRET-OFF processes with ratiometric PL behavior of the bifluorophoric supramolecular [2]pseudo-rotaxane polymer will open a new avenue to the future applications of chemo- and biosensors.

Low molecular weight self-assembling peptide-based materials for cell culture, antimicrobial, anti-inflammatory, wound healing, anticancer, drug delivery, bioimaging and 3D bioprinting applications

In this review, we have focused on the design and development of low molecular weight self-assembling peptide-based materials for various applications including cell proliferation, tissue engineering, antibacterial, antifungal, anti-inflammatory, anticancer, wound healing, drug delivery, bioimaging and 3D bioprinting. The first part of the review describes about stimuli and various noncovalent interactions, which are the key components of various self-assembly processes for the construction of organized structures. Subsequently, the chemical functionalization of the peptides has been discussed, which is required for the designing of self-assembling peptide-based soft materials. Various low molecular weight self-assembling peptides have been discussed to explain the important structural features for the construction of defined functional nanostructures. Finally, we have discussed various examples of low molecular weight self-assembling peptide-based materials for cell culture, antimicrobial, anti-inflammatory, anticancer, wound healing, drug delivery, bioimaging and 3D bioprinting applications.

Naphthalimide Imidazolium-Based Supramolecular Hydrogels as Bioimaging and Theranostic Soft Materials

1,8-Naphthalimide-based imidazolium salts differing for the alkyl chain length and the nature of the anion were synthesized and characterized to obtain fluorescent probes for bioimaging applications. First, their self-assembly behavior and gelling ability were investigated in water and water/dimethyl sulfoxide binary mixtures. Only salts having longer alkyl chains were able to give supramolecular hydrogels, whose properties were investigated by using a combined approach of fluorescence, resonance light scattering, and rheology measurements. Morphological information was obtained by scanning electron microscopy. In addition, conductive properties of organic salts in solution and gel state were analyzed. Imidazolium salts were successfully tested for their possible application as bioimaging and cytotoxic agents toward three cancer cell lines and a nontumoral epithelial cell line. Characterization of their behavior was performed by MTT and cell-based assays. Finally, the biological activity of hydrogels was also investigated. Collectively, our findings showed that naphthalimide-based imidazolium salts are promising theranostic agents and they were able to preserve their biological properties also in the gel phase.

Live cell imaging by 3-imino-(2-phenol)-1,8-naphthalimides: The effect of ex vivo hydrolysis

A series of 3-amino-N-substituted-1,8-naphthalimides and their salicylic Schiff base derivatives were synthesized. The structure of the obtained compounds was confirmed using ¹H and ¹³C NMR, FT-IR spectroscopy and elemental analysis and COSY and HMQC for the representative molecules. The photophysical (UV-Vis, PL) and biological properties of all of the prepared compounds were studied. It was found that the amine with the n-hexyl group in EtOH had the highest PL quantum yield (Ф = 85%) compared to the others. Moreover, the chelating properties of the azomethines with the n-hexyl group (1a, 1b, 1c) were tested against various cations (Al³⁺, Ba²⁺, Co²⁺, Cu²⁺, Cr³⁺, Fe²⁺, Fe³⁺, Mn²⁺, Ni²⁺, Pb²⁺, Sr²⁺ and Zn²⁺) in an acetonitrile, acetone and PBS/AC mixture. Compounds that contained the electron withdrawing groups (-Br, -I) had the ability to chelate most of the studied cations, while the unsubstituted derivative chelated only the trivalent cations such as Al³⁺, Cr³⁺ and Fe³⁺ in acetonitrile. The effect of the environment on the keto-enol tautomeric equilibrium was also demonstrated, especially in the case of the derivative with a bromine atom. The biological studies showed that the tested molecules had no cytotoxicity. Additionally, the ability to image intracellular organelles such as the mitochondria and endoplasmic reticulum was revealed. The crucial role of the hydrolysis of imines for cellular imaging was presented.

rkDNA-graphene oxide as a simple probe for the rapid detection of miRNA21

In this study we developed a novel diagnostic tool for the detection of miRNA21, based on the fluorescent nucleotide morpholine naphthalimide deoxyuridine (dUrkTP). We incorporated dUrkTP into DNA through primer extension to obtain rkDNA displaying high fluorescence. We then used lambda exonuclease, a specific nuclease for 3́-monophosphate-containing DNA, to separate rkDNA from its complementary sequence. The fluorescence of the free rkDNA was quenched dramatically upon interacting with graphene oxide (GO). Our rkDNA-GO fluorescence probing system exhibited high sensitivity and selectivity for the detection of miRNA21. This inexpensive probing system, employing simple primer extension and exonuclease degradation, required only 30 min to detect its target miRNA. This strategy appears suitable for the detection of diverse types of miRNA.

Enzyme Instructed Self-assembly of Naphthalimide-dipeptide: Spontaneous Transformation from Nanosphere to Nanotubular Structures that Induces Hydrogelation

Understanding the structure-morphology relationships of self-assembled nanostructures is crucial for developing materials with the desired chemical and biological functions. Here, phosphate-based naphthalimide (NI) derivatives have been developed for the first time to study the enzyme-instructed self-assembly process. Self-assembly of simple amino acid derivative NI-Yp resulted in non-specific amorphous aggregates in the presence of alkaline phosphatase enzyme. On the other hand, NI-FYp dipeptide forms spherical nanoparticles under aqueous conditions which slowly transformed into partially unzipped nanotubular structures during the enzymatic catalytic process through multiple stages which subsequently resulted in hydrogelation. The self-assembly is driven by the formation of β-sheet type structures stabilized by offset aromatic stacking of NI core and hydrogen bonding interactions which is confirmed with PXRD, Congo-red staining and molecular mechanical calculations. We propose a mechanism for the self-assembly process based on TEM and spectroscopic data. The nanotubular structures of NI-FYp precursor exhibited higher cytotoxicity to human breast cancer cells and human cervical cancer cells when compared to the nanofiber structures of the similar Fmoc-derivative. Overall this study provides a new understanding of the supramolecular self-assembly of small-molecular-weight hydrogelators.

A Highly Selective Fluorescent Probe for Hg2+ Based on a 1,8-Naphthalimide Derivative

Hg2+ has a significant hazardous impact on the environment and ecosystem. There is a great demand for new methods with high selectivity and sensitivity to determine mercury in life systems and environments. In this paper, a novel turn-on Hg2+ fluorescent probe has been reported with a naphthalimide group. The Hg2+ fluorescent probe was designed by the inspiration of the well-known specific Hg2+-triggered thioacetal deprotection reaction. A 1,2-dithioalkyl group was chosen as the specific recognition site of Hg2+. The probe showed weak fluorescence without Hg2+, and the color of the solution was light yellow. In the presence of Hg2+, the probe reacted specifically with the mercury ion to produce an aldehyde and emitted strong fluorescence, and the color of the solution also turned light green, thus realizing the monitoring of the mercury ion. The Hg2+ fluorescent probe showed outstanding sensitivity and selectivity toward Hg2+. Furthermore, the Hg2+ fluorescent probe could work in a wide pH range. The linear relationship between the fluorescence intensity at 510 nm and the concentration of Hg2+ was obtained in a range of Hg2+ concentration from 2.5 × 10-7 to 1.0 × 10-5 M. The detection limit was found to be 4.0 × 10-8 M for Hg2+. Furthermore, with little cell toxicity, the probe was successfully applied to the confocal image of Hg2+ in PC-12 cells.

Perylene diimides: will they flourish as reaction-based probes?

Perylene diimides (PDI) are a well-studied class of functional organic dyes, and in recent years, they have been accepted as promising scaffolds for the design of small molecule/polymer-based chromogenic and fluorogenic reaction-based-probes because of their strong absorption combined with high fluorescence quantum yield in organic solvents, low reduction potential, good electron-acceptor properties, and broad color range properties. Undoubtedly, the intrinsically poor solubility of PDI-based derivatives in water greatly hampers their exploitation as reaction-based probes; however, a vast array of functionalizations now offer design strategies that have resulted in >50% solubility of PDI derivatives in water. A chemodosimeter, wherein chemical transformation is achieved by specific reactions, affords naked-eye visibility, fast response time, sensitivity, ratiometric response, and low cost. The present review focuses on the progress of PDI-based chemodosimeters achieved so far since the inception of this member in the rylene diimide family. This comprehensive review may facilitate the development of more powerful chemodosimeters based on PDI for broad and exciting applications in the future.

Developing fluorescent copper nanoclusters: Synthesis, properties, and applications

Metal nanoclusters exhibit strong fluorescence emission, providing immense potential for developments in biological labeling and imaging. Copper nanoclusters in particular, due to their unique optical properties such as molecular-like absorption and strong luminescence, represent a novel fluorescent nanomaterial for sensing and bioimaging applications. This review describes research progress on Cu nanoclusters in recent years, investigating the synthesis techniques, their properties, and their promising applications. A concluding summary provides an outlook on the future research challenges for Cu nanoclusters and their corresponding synthesis techniques.

1,8-Naphthalimide-Based Polymers Exhibiting Deep-Red Thermally Activated Delayed Fluorescence and Their Application in Ratiometric Temperature Sensing

A series of naphthalimide (NAI)-based red-emissive thermally activated delayed fluorescence (TADF) acrylic monomers has been designed and synthesized. When copolymerized with a host material by Cu(0)-reversible deactivation radical polymerization (Cu(0)-RDRP), polymers exhibiting orange to deep-red TADF were obtained with quantum yields of up to 58% in solution and 31% in the solid state. These emitters exhibit dual emission consisting of high-energy prompt fluorescence from the NAI acceptor (λ_max = 340 nm in toluene) and red-delayed fluorescence from the charge-transfer process (λ_max = 633-711 nm in toluene). This dual emissive property was utilized to create red-to-blue temperature-responsive polymers by copolymerization of NAI-DMAC with N-isopropylacrylamide and a blue fluorescent dopant. These polymers exhibit red TADF at room temperature and blue fluorescence at 70 °C, with a high ratiometric fluorescent thermal response of 32 ± 4% K^-1. Such systems are anticipated to have utility in bioimaging, drug delivery, and temperature sensing, further expanding the range of applications for red TADF materials.

A Polyamine-Based Dinitro-Naphthalimide Conjugate as Substrates for Polyamine Transporters Preferentially Accumulates in Cancer Cells and Minimizes Side Effects in vitro and in vivo

Naphthalimides, such as amonafide and mitonafide in clinical trials, have been developed as antitumor agents for orthotopic tumor. However, the serious side effects in cancer patients limit their applications. Herein, a new class of polyamine-based naphthalimide conjugates 5a-5c, 7a-7b, and 11a-11b with and without the alkylation of the distant nitrogen in the polyamine chain were synthesized and the mechanism was determined. Compared with amonafide, dinitro-naphthalimide conjugate 5c with a 4,3-cyclopropyl motif preferentially accumulates in cancer cells and minimizes side effects in vitro and in vivo. More importantly, 5c at the dosage of as low as 3 mg/kg (57.97%) displays better antitumor effects than the positive control amonafide (53.27%) at 5 mg/kg in vivo. And a remarkably elevated antitumor activity and a reduced toxicity are also observed for 5c at 5 mg/kg (65.90%). The upregulated p53 and the apoptotic cells (73.50%) indicate that the mechanism of 5c to induce apoptosis may result from its enhanced DNA damage. Further investigation indicates that in addition to target DNA, 5c can modulate the polyamine homeostasis by upregulating polyamine oxidase (PAO) in a different way from that of amonafide. And also by targeting PTs overexpressed in most of cancer cells, 5c downregulates the contents of Put, Spd, and Spm, which are in favor of suppressing fast-growing tumor cells. Our study implies a promising strategy for naphthalimide conjugates to treat hepatic carcinoma with notable activities and reduced toxicities at a low dosage.

An AIE fluorescent probe with a naphthalimide derivative and its application for detection of hypochlorite and imaging inside living cells

Hypochlorite (ClO^-) is a highly reactive oxygen species that plays an important role in resistance to attacks by microorganisms. Herein, we report the preparation of a fluorescence probe (NIB-M) through the integration of a naphthalimide moiety and ClO^- to capture diaminomaleonitrile and employ it for the aggregation-induced emission-based (AIE-based) monitoring of ClO^-. In the presence of ClO^-, NIB-M undergoes sequential nucleophilic substitution and HCl elimination reactions that allow it to possess high selectivity, a fast response, and a low detection limit (0.032 μM). Due to the good AIE properties of the parent molecule, a ClO^- test board was facilely prepared by loading NIB-M on a Whatman paper strip-based portable device. The test plate can conveniently and sensitively detect hypochlorite onsite. In addition, the NIB-M probe was used for the imaging of exogenous/endogenous ClO^- inside living cells.

ICT and AIE Characteristics Two Cyano-Functionalized Probes and Their Photophysical Properties, DFT Calculations, Cytotoxicity, and Cell Imaging Applications

Two probes, AIE-1 and AIE-2, were synthesized to investigate the effect of substitutional functional group on aggregation (aggregation-caused quenching (ACQ) or aggregation-induced emission (AIE)) and intramolecular charge transfer (ICT) behavior as well as on the cell imaging aspect. The yellow-color non-substituted probe AIE-1 showed weak charge-transfer absorption and an emission band at 377 nm and 432 nm, whereas the yellowish-orange color substituted probe AIE-2 showed a strong charge-transfer absorption and an emission band at 424 nm and 477 nm in THF solvent. The UV-Vis studies of AIE-1 and AIE-2 in THF and THF with different water fractions showed huge absorption changes in AIE-2 with high water fractions due to its strong aggregation behavior, but no such noticeable absorption changes were observed for AIE-1. Interestingly, the fluorescence intensity of AIE-1 at 432 nm gradually decreased with increasing water fractions and became almost non-emissive at 90% water. However, the monomer-type emission of AIE-2 at 477 nm was shifted to 584 nm with a 6-fold increase in fluorescence intensity in THF-H2O (1:9, v/v) solvent mixtures due to the restriction of intramolecular rotation on aggregation in high water fractions. This result indicates that the probe AIE-1 shows ACQ and probe AIE-2 shows AIE behaviors in THF-H2O solvent mixtures. Furthermore, the emission spectra of AIE-1 and AIE-2 were carried out in different solvent and with different concentrations to see the solvent- or concentration-dependent aggregation behavior. Scanning electron microscope (SEM) and dynamic light scattering (DLS) experiments were also conducted to assess the morphology and particle size of two probes before and after aggregation. Both of the probes, AIE-1 and AIE-2, showed less toxicity on HeLa cells and were suitable for cell imaging studies. Density functional theory (DFT) calculation was also carried out to confirm the ICT process from an electron-rich indole moiety to an electron-deficient cyano-phenyl ring of AIE-1 or AIE-2.

Modulation of circularly polarized luminescence through excited-state symmetry breaking and interbranched exciton coupling in helical push-pull organic systems

π-Helical push-pull dyes were prepared and their (chir)optical properties were investigated both experimentally and computationally. Specific fluorescent behaviour of bis-substituted system was observed with unprecedented solvent effect on the intensity of circularly polarized luminescence (CPL, dissymmetry factor decreasing from 10-2 to 10-3 with an increase in solvent polarity) that was linked to a change in symmetry of chiral excited state and suppression of interbranched exciton coupling. The results highlight the potential of CPL spectroscopy to study and provide a deeper understanding of electronic photophysical processes in chiral π-conjugated molecules.

Aggregation induced emission (AIE) active 4-amino-1,8-naphthalimide-Tröger's base for the selective sensing of chemical explosives in competitive aqueous media

The 4-amino-1,8-naphthalimide Tröger's base based AIE-active supramolecular scaffold was synthesized and employed as a highly selective and sensitive fluorescent sensor for nitroaromatic explosives sensing in competitive aqueous media.

Synthesis and investigation of the photophysical, electrochemical and theoretical properties of phenazine–amine based cyan blue-red fluorescent materials for organic electronics

We report a study of the effect of modulating the donor system fused with a central phenazine core to understand the tuning of the optoelectrochemical properties in the designed phenazine–amine derivatives.

Naphthalimide-containing coordination polymer with mechanoresponsive luminescence and excellent metal ion sensing properties

Mechanoresponsive luminescent materials coupled with other functionalities are of particular interest due to their multiple external stimuli responsive properties. In this paper, a new sensitive mechanoresponsive luminescent coordination polymer, [Cd(INI)(DMF)2·DMF] (1) (H2INI = N-(5-isophthalic acid)-1,8-naphthalimide), has been successfully designed and synthesized. Complex 1 exhibits interesting mechanoresponsive and grinding-enhanced luminescence properties, and its luminescence colour changed from weak blue-green to bright blue upon grinding owing to the external pressure-induced destruction of ππ stacked arrangements in local defective areas. Moreover, the luminescence properties and uncoordinated carbonyl groups of well-ground g-1 endow it with excellent sensing ability for Cr3+ ions. This work will provide a new perspective to rationally design multifunctional coordination polymers that can serve as practical multi-responsive sensors to pressure and chemicals.

Fluorescence detection of phosphonates in water by a naphthalimide-based receptor and its derived cryopolymers

The concentration of compound M in cryopolymers has a dramatic influence on the fluorescence response in the presence of phosphonates.

A novel “turn-on” fluorescent probe based on naphthalimide for the tracking of lysosomal Cu2+ in living cells

The lysosome-targeted probe CuNI exhibits highly effective fluorescence detection ability for Cu²⁺ in aqueous solution and cells. The fluorescent enhancement is due to the Cu²⁺-catalyzed hydrolysis of CuNI and the AIE effect of the hydrolysate MFNI.

Fluorescent supramolecular hierarchical self-assemblies from glycosylated 4-amino- and 4-bromo-1,8-naphthalimides

The investigation into the self-assembly formation of the glycan based 4-amino- and 4-bromo-1,8-naphthalimide (Nap) structures1–3is presented.

An Unprecedented Blueshifted Naphthalimide AIEEgen for Ultrasensitive Detection of 4-Nitroaniline in Water via "Receptor-Free" IFE Mechanism

The development of a new naphthalene appended naphthalimide derivative (NMI) with aggregation-induced enhanced emission (AIEE) property for the sensitive detection of 4-nitroaniline (4-NA) in aqueous media is presented here. The newly designed naphthalimide AIEEgen has an exceptional blue-shifted condensed state emission that is devoid of any receptor site, accomplished ultrasensitive detection of 4-NA, which is one of the broad-spectrum pesticides that belong to the class III toxic chemical, at parts per billion level (LOD/36 ppb, K_sv =4.1×10⁴  m^-1 ) in water with excellent selectivity even in the presence of potentially competing aliphatic and aromatic amines. The reported probe is the first of its kind, demonstrating major advantages of receptor-free inner filter effect (IFE) mechanism for the sensitive detection of 4-NA using an AIEEgenic probe. Excellent sensitivity for 4-NA is also achieved on paper-based test-strip for low-cost on-site detection.

AIE-active fluorescent polymeric nanoparticles about dextran derivative: preparation and bioimaging application

Aggregation-induced emission (AIE), as a special phenomenon of fluorescence, can elegantly overcome the fluorescence quenching caused by common fluorescent materials under high concentration conditions and has attracted interest of researchers in many fields. Particularly AIE-active polymer nanoparticles have been widely utilized in a modern biomedical research. In this work, we prepared a novel kind of AIE-active fluorescent polymeric nanoparticals (Dex-OH-CHO) through a facile esterification between a new hydrophobic AIE-active 1, 8-naphthalimide derivative and the hydrophilic dextran. The structure and optical properties of Dex-OH-CHO were characterized in detail by FTIR, ¹H NMR, XPS, TEM and fluorescence spectra. The results showed that Dex-OH-CHO emitted light-blue fluorescence in aqueous solution with high fluorescent quantum yield (Φ = 24.43%, concentration is 20 μg/mL), low CMC (5 μg/mL), good photostability, high water solubility and well dispersivity. Moreover, good biocompatibility and ideal cell uptake made Dex-OH-CHO had a great application potential in biological imaging.

Alkyl Conformation and π-π Interaction Dependent on Polymorphism in the 1,8-Naphthalimide (NI) Derivative

The 1,8-naphthalimide (NI) derivative Lumogen F Violet 570 exhibits different photoluminescence (PL) and aggregation-caused quenching properties due to its crystal polymorphism, which depends on the solvent evaporation process in tetrahydrofuran solution. In the slow drying process, molecules aggregated into an energetically more stable form (time-dependent density functional theory calculation), of which the PL peak maximum was 453 nm, corresponding to blue emission at the 365 nm excitation. However, the fast evaporation process induces an energetically less stable form, with a PL peak maximum of 508 nm, corresponding to green emission. The main difference between the two crystal structures is the alkyl conformation, as confirmed by X-ray single-crystal analysis. Due to the different alkyl conformations, NI groups aggregated into more obliquely aligned structures that emit blue PL, which plays a role in weakening the π-π interactions between molecules relative to green PL crystals. We found that the conformational stable molecular stacking induced instability in the electronic energy levels of the blue crystal compared to the green crystal.

A benzothiazole-rhodol based luminophor: ESIPT-induced AIE and an application for detecting Fe2+ ion

Herein, we designed and synthesized a luminophor, Rh-F, which is an intergrant of rhodol and 2-hydroxy benzothiazole by introducing a benzothiazole unit onto the ortho-position of the phenolic hydroxy of rhodol. Rh-F exhibited excellent fluorescence properties such as a large Stokes shift (>180 nm) and the synergistic effect of aggregation-induced emission (AIE) and an excited state intramolecular proton transfer (ESIPT) feature. The AIE/ESIPT mechanism was thoroughly explored using X-ray single-crystal structures and photophysical determinations. Furthermore, Rh-F showed a sensitive fluorescence response to Fe²⁺ with low detection limits of 115.2 nM and high selectivity. Studies of its sensing mechanism indicated that the Fe²⁺-induced blue-green fluorescence-quenched at 525 nm originates from an irreversible Fe²⁺ chelate with the oxygen atom of the hydroxyl group and the N atom of the benzothiazole moiety. This blocked the ESIPT process of Rh-F which resulted in the quenching of the fluorescence sensor for Rh-F.

A novel bis-component AIE smart gel with high selectivity and sensitivity to detect CN-, Fe3+ and H2PO4. SOFT MATTER 2019;15:6348-6352. [PMID: 31290897 DOI: 10.1039/c9sm01035a]

A novel bis-component AIE-gel TG was facilely constructed from two "easy-to-synthesize" tripodal gelators by a simple host-guest self-assembly process. Interestingly, the TG shows strong aggregation-induced emission (AIE) and could be used for highly efficient and sensitive detection and separation of ions (CN^-, Fe³⁺ and H₂PO₄^-). The LODs (limits of lowest detection) of TG for CN^-, Fe³⁺ and H₂PO₄^- are in the range of 4.93 × 10^-9-7.80 × 10^-8 M. Meanwhile, the xerogel of TG could adsorb and separate Fe³⁺ from aqueous solutions, and the adsorption rate is 96%. In addition, a thin film based on the TG could act as a convenient test kit for the detection of CN^- and Fe³⁺. What is more, the TG-Fe film could not only be used as an erasable secure fluorescent display material, but also as a convenient reversible H₂PO₄^- test kit.

A Naphthalimide-Benzothiazole Conjugate as Colorimetric and Fluorescent Sensor for Selective Trinitrophenol Detection

Although chemical structural modification of naphthalimides is widely employed for the purpose of sensing explosives, the effects of such modification have been little explored. Herein, we report the design and synthesis of a new naphthalimide-benzothiazole conjugate (1) and its ability to sense various nitrophenols by means of its colorimetric and fluorescent characteristics. Under long-range UV light (365 nm), 1 displayed a color change of its solution from bluish to colorless only upon addition of 2,4,6-trinitrophenol (TNP). Photoluminescence spectroscopy showed quantitative fluorescence quenching by TNP of the emission peaks of 1 at 398 nm and 418 nm due to donor–acceptor electron transfer. The interaction of 1 with TNP was via a cooperative, non-covalent hydrogen-bonding interaction. Receptor 1 exhibited high sensitivity and selectivity towards TNP over various aromatic nitro analytes. The binding constant (K) and Stern–Volmer constant (Ksv) between 1 and TNP were found to be 5.332 × 10−5 M and 2.271 × 106 M−1, respectively. Furthermore, the limit of detection was calculated and found to be as low as 1.613 × 10−10 M.

Recent Advances in Aggregation-Induced Electrochemiluminescence

The emergence of the rising alliance between aggregation-induced emission (AIE) and electrochemiluminescence (ECL) is defined as aggregation-induced electrochemiluminescence (AIECL). The booming science of AIE has proved to be not only distinguished in luminescent materials but could also inject new possibility into ECL analysis. Especially in the aqueous phase and solid state for hydrophobic materials, AIE helps ECL circumvent the dilemma between substantial emission intensity and biocompatible media. The wide range of analytes makes ECL an overwhelmingly interesting analytical technique. Therefore, AIECL has gained potential in clinical diagnostics, environmental assays, and biomarker detections. This review will focus on introduction of the novel concept of AIECL, current applied luminophores, and related applications developed in recent years.

Functional group engineering in naphthalimides: a conceptual insight to fine-tune the supramolecular self-assembly and condensed state luminescence

Engineering well-defined supramolecular fluorescent nano-architectures based on organic conjugated small molecules has been an essential scientific challenge. Herein, a library of sixteen naphthalimide congeners (1-15 and HNI) has been strategically designed that unveils a conceptual insight into the functional group controlled condensed state emission and aggregation-induced enhanced emission (AIEE) in conventional strong aggregation-caused quenching (ACQ) active fluorophores. Along with the regulation of ACQ-to-AIEE transformation and tailoring of the condensed state emission, a simple yet potential design strategy of functional group engineering has been established for the first time to spontaneously generate and systematically tailor the supramolecular self-assembly of organic small molecules into highly defined nano-architectures. Single-crystal XRD analysis of six congeners revealed that, unlike the well-established electronic contribution of the functional groups in the molecularly dispersed state, the condensed state photophysical and morphological properties are dictated by the distinct intermolecular π-π stacking interaction of the planar aromatic core. This work demonstrates an unconventional influence of the functional motif in the condensed state that could emerge as a promising route to build a fluorescent supramolecular nanoassembly from non-fluorescent conjugated molecules for a variety of future applications.

Color-Tunable and Stimulus-Responsive Luminescent Liquid Crystalline Polymers Fabricated by Hydrogen Bonding

Luminescent liquid crystalline polymers (LLCPs) show extensive application potentials, such as liquid crystal displays and circularly polarized luminescence. In this work, we employ a hydrogen-bonding strategy different from the traditional covalent-bonding method to fabricate LLCPs. First, the acceptor and donor of hydrogen bonding, (4,4'-dibutanoxy tetraphenylethylene)-1-pyridine (PTPEC₄) and poly(2-vinyl terephthalic acid) (PPA), respectively, are successfully synthesized. Then, mixtures with different molar ratios ( x's) of PTPEC₄ to PPA are used to prepare a series of LLCPs [denoted as PPA(PTPEC₄) _x]. The resultant LLCPs show a smectic A phase ( x ≥ 0.8), a columnar nematic phase (0.6 ≤ x ≤ 0.05), and an amorphous state ( x = 0.025), depending on the x value. Meanwhile, all polymers exhibit typical aggregation-induced emission behavior. More interestingly, with the variation of the PTPEC₄ content, the series of LLCPs show different colors, that is, the emission peak red shifts from 510 nm ( x = 1.0) to 551 nm ( x = 0.025). Furthermore, because of the reversible protonation effect of the N atom of pyridine in PTPEC₄ by the strong proton acid, PPA(PTPEC₄) _x shows reversible color transformation. This work provides a new method to construct LLCPs with different emission colors and reversible color transformation.

Insight into the delivery channel and selectivity of multiple binding sites in bovine serum albumin towards naphthalimide-polyamine derivatives

Naphthalimide derivatives are types of small-molecule anticancer drug candidates; however, their negative factors and potential side effects make their application limited. The pharmacophores select a direct access into the tumor cells as the first choice; this can reduce the side effect of the anti-cancer drugs on the normal cells. Herein, the delivery and binding of the naphthalimide-polyamine complex assisted by the bovine serum albumin (BSA) protein have been studied by combining several molecular dynamic simulations. The plausible transportation channels and the most favorable pathways for the delivery of the naphthalimide-polyamine complex to two drug sites (DSI and DSII), their thermodynamic and dynamic properties and the mechanisms have been discussed in detail. The residues His287 and Phe394 acted as guards in the DSI and DSII, respectively, which played a gating-switch role by flipping the ring from open to close during the compound delivery. The binding mode, binding energy and substituent effects have been also identified. The two drug sites have different preferences towards the compound with the electron-withdrawing and electron-donating substituents, and their strong interactions are more sensitive to the number of the substituent groups. The naphthalimide-polyamine complexes are more likely to choose DSI, both thermodynamically and dynamically, as compared to DSII. This selective specificity of these two drug sites manipulated by the electron-withdrawing and electron-donating substituents is quite promising for the design of new naphthalimide drugs.

Anion induced supramolecular polymerization: a novel approach for the ultrasensitive detection and separation of F−

A novel approach for the ultrasensitive detection and separation of F⁻ has been developed. F⁻ could induce a tripodal naphthalimide sensor (TNA) to carry out reversible supramolecular polymerization and lead to strong AIEE.