Naphthalene diimide based near-infrared luminogens with aggregation-induced emission characteristics for biological imaging and high mobility ambipolar transistors

Aggregation-Induced Emission of Naphthalene Diimides: Effect of Chain Length on Liquid and Solid-Phase Emissive Properties

The aggregation-induced emission (AIE) properties of a systematic series of naphthalene diimides (NDIs) varying the chain length at the imide positions have been studied. A solvophobic collapse of NDI units through the flash injection of THF NDI solutions in sonicating water triggers the formation of stable suspensions with enhanced fluorescence emissions. Shorter chains favor the π-π stacking of NDI units through H-aggregation producing a strong AIE effect showing remarkably high quantum yields that have not been observed for non core-substitued NDIs previously. On the other hand, NDIs functionalized with longer chains lead to more disordered domains where π-π stacking between NDI units is mainly given by J-aggregation unfavoring the AIE effect.

Synthesis, Photophysical Properties and Self-Assembly of a Tetraphenylethylene-Naphthalene Diimide Donor-Acceptor Molecule

The development of new π-conjugated molecular structures with controlled self-assembly and distinct photophysical properties is crucial for advancing applications in optoelectronics and biomaterials. This study introduces the synthesis and detailed self-assembly analysis of tetraphenylethylene (TPE) functionalized naphthalene diimide (NDI), a novel donor-acceptor molecular structure referred to as TPE-NDI. The investigation specifically focuses on elucidating the self-assembly behavior of TPE-NDI in mixed solvents of varying polarities, namely chloroform: methylcyclohexane (CHCl3 : MCH) and chloroform: methanol (CHCl3 : MeOH). Employing a several analytical methodologies, including UV-Vis absorption and fluorescence emission spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), and dynamic light scattering (DLS), these self-assembled systems have been comprehensively examined. The results reveal that TPE-NDI manifests as distinct particles in CHCl3 : MCH (fMCH =90 %), while transitioning to flower-like assemblies in CHCl3 : MeOH (fMeOH =90 %). This finding underscores the critical role of solvent polarity in dictating the morphological characteristics of TPE-NDI self-assembled aggregates. Furthermore, the study proposes a molecular packing mechanism, based on SEM data, offering significant insights into the design and development of functional supramolecular systems. Such advancements in understanding the molecular self-assembly new π-conjugated molecular structures are anticipated to pave the way for novel applications in material science and nanotechnology.

Recent advances in n-type and ambipolar organic semiconductors and their multi-functional applications

Organic semiconductors have received broad attention and research interest due to their unique integration of semiconducting properties with structural tunability, intrinsic flexibiltiy and low cost. In order to meet the requirements of organic electronic devices and their integrated circuits, p-type, n-type and ambipolar organic semiconductors are all necessary. However, due to the limitation in both material synthesis and device fabrication, the development of n-type and ambipolar materials is quite behind that of p-type materials. Recent development in synthetic methods of organic semiconductors greatly enriches the range of n-type and ambipolar materials. Moreover, the newly developed materials with multiple functions also put forward multi-functional device applications, including some emerging research areas. In this review, we give a timely summary on these impressive advances in n-type and ambipolar organic semiconductors with a special focus on their synthesis methods and advanced materials with enhanced properties of charge carrier mobility, integration of high mobility and strong emission and thermoelectric properties. Finally, multi-functional device applications are further demonstrated as an example of these developed n-type and ambipolar materials.

The commercial antibiotics with inherent AIE feature: In situ visualization of antibiotic metabolism and specifically differentiation of bacterial species and broad-spectrum therapy

The research on pharmacology usually focuses on the structure-activity relationships of drugs, such as antibiotics, to enhance their activity, but often ignores their optical properties. However, investigating the photophysical properties of drugs is of great significance because they could be used to in situ visualize their positions and help us to understand their working metabolism. In this work, we identified a class of commercialized antibiotics, such as levofloxacin, norfloxacin, and moxifloxacin (MXF) hydrochloride, featuring the unique aggregation-induced emission (AIE) characteristics. By taking advantage of their AIE feature, antibiotic metabolism in cells could be in situ visualized, which clearly shows that the luminescent aggregates accumulate in the lysosomes. Moreover, after a structure-activity relationship study, we found an ideal site of MXF to be modified with a triphenylphosphonium and an antibiotic derivative MXF-P was prepared, which is able to specifically differentiate bacterial species after only 10 min of treatment. Moreover, MXF-P shows highly effective broad-spectrum antibacterial activity, excellent therapeutic effects and biosafety for S. aureus-infected wound recovery. Thus, this work not only discovers the multifunctionalities of the antibiotics but also provides a feasible strategy to make the commercialized drugs more powerful.

AIE-Active Antibiotic Photosensitizer with Enhanced Fluorescence in Bacteria Infected Cells and Better Therapy Effect toward Drug-Resistant Bacteria

It is well-known that bacterial infections will induce a variety of diseases in the clinic. In particular, the emergence of drug-resistant bacteria has increased the threat to human health. The development of multiple modes of therapy will effectively fight against drug-resistant bacterial infections. In this work, we covalently attached an AIE photosensitizer to the antibiotic of moxifloxacin hydrochloride (MXF-HCl) and synthesized an antibiotic derivative, MXF-R, with pharmacological activity and photodynamic activation. In infected cells, MXF-R showed enhanced fluorescence after it specifically binds to bacteria; thus, in situ visualization of the bacteria was realized. Notably, through chemo- and photodynamic therapy, MXF-R exhibited better antibacterial activity than its parent antibiotic in rapid sterilization, and it achieved effective killing for moxifloxacin resistant bacteria. In addition, MXF-R shows a broad-spectrum antibacterial effect and could be used in the recovery therapy of infected wounds in mice, demonstrative of a significant therapeutic effect and good biological safety. Thus, as a promising multifunctional antibacterial agent, MXF-R will have tremendous potential in in situ visualization study and killing of drug-resistant bacteria. This work provides an innovative strategy for solving critical disease through the combination of materials and biomedical sciences.

Room-Temperature Phosphorescence of Nicotinic Acid and Isonicotinic Acid: Efficient Intermolecular Hydrogen-Bond Interaction in Molecular Array

Pure organic room-temperature phosphorescence (RTP) has attracted wide interest due to its unique advantages and promising applications. However, it is still challenging to develop efficient RTP through precise molecular design. In this work, RTP is observed from two simple aromatic acids, nicotinic acid (NA) and isonicotinic acid (INA), in the crystal state. Single crystal structure analysis indicates that an intense hydrogen bond between the pyridine nitrogen atom and the carboxyl group results in zigzag and linear molecular packing modes in NA and INA crystal. From theoretical calculations, the hydrogen bond can effectively promote the intersystem crossing process and stabilize triplet exciton. The identical molecular orientations in the molecular array contribute to the larger dipole moment of INA as compared to that of NA, which should be responsible for the red-shifted photoluminescence and RTP of INA. When the hydrogen bond is destructed by grinding or deprotonation, the RTP decreases sharply, further confirming the crucial role of the hydrogen bond on RTP.

An asymmetric 2,3-fluoranthene imide building block for regioregular semiconductors with aggregation-induced emission properties

For organic semiconductors, the development of electron-deficient building blocks has lagged far behind that of the electron-rich ones. Moreover, it remains a significant challenge to design organic molecules with efficient charge transport and strong solid-state emission simultaneously. Herein, we describe a facile synthetic route toward a new π-acceptor imide building block, namely 2,3-fluoranthene imide, based on which four regioregular small molecules (F1–F4) are synthesized by tuning the imide orientations and the central linkage bridges. All molecules exhibit attractive aggregation-induced emission (AIE) characteristics with strong far-red emission in the powder state, and F3 shows the highest photoluminescence quantum yield of 5.9%. F1 and F3 with a thiophene bridge present an obvious p-type characteristic, while for F3 with an outward imide orientation, the maximum hole mobility from a solution-processed field-effect transistor (FET) device reaches 0.026 cm² V⁻¹ s⁻¹, being ∼10⁴ times higher than the value of F1 with an inward imide orientation. By using a fluorinated thiophene bridge, the resulting F2 and F4 can be turned into n-type semiconductors, showing an electron mobility of ∼1.43 × 10⁻⁴ and ∼3.34 × 10⁻⁵ cm² V⁻¹ s⁻¹, respectively. Our work not only demonstrates that asymmetric 2,3-fluoranthene imide is a promising building block for constructing organic materials with high carrier mobility and strong solid-state emission, but also highlights the importance of regioregular structures in the materials' properties.

A new electron-deficient 2,3-fluoranthene imide unit was easily synthesized through a one-pot reaction for constructing small molecule regioregular semiconductors with good carrier transport ability and strong solid-state emission.

Aggregation-Induced Emission Materials that Aid in Pharmaceutical Research

The in situ visualization of drugs can improve the understanding of their pharmacokinetics and mechanisms. Aggregation-induced emission (AIE) materials, which can aid in the visualization of drugs, are gradually being employed in pharmaceutical research due to their excellent fluorescence properties, good biocompatibility, and extremely high sensitivity. Herein, the progress of AIE materials in pharmaceutical research, including AIE carriers for drug delivery, AIE multifunctional prodrugs, and AIE compounds as bioactive reagents for theranostics is briefly described. Moreover, the opportunities and challenges of AIE materials in pharmaceutical research are discussed in depth. It is believed that versatile AIE materials hold great promise for the promotion of pharmacological research and can facilitate significant advancements in clinical fields.

Diversity of Luminescent Metal Complexes in OLEDs: Beyond Traditional Precious Metals

Organic light-emitting diodes (OLED) have attracted increasing attention due to their excellent properties, such as self-luminosity, high color gamut and flexibility, and potential applications in display, wearable devices and lighting. The emitters are the most important composition in OLEDs, mainly classified into fluorescent compounds (first generation), metal phosphorescent complexes (second generation), and thermally activated delayed fluorescence (TADF) materials (third generation). In this review, we summarize the advances of novel emitters of organic metal complexes in the last decade, focusing on coinage metals (Cu, Ag, and Au) and non-precious metals (Al, Zn, W, and alkali metal). Also, the design strategy of d¹⁰ and Au(III) complexes was discussed. We aim to provide guidance for exploring efficient metal complexes beyond traditional phosphorescent complexes.

Cationic Tricyclic AIEgens for Concomitant Bacterial Discrimination and Inhibition

New ionic compounds with aggregation-induced emission (AIE) feature has been widely studied. These AIE-based luminogens (AIEgens) not only effectively resolve aggregation-caused quenching (ACQ) problems that are encountered for most of conventional fluorescent dyes, but also exhibit promising applications in biological imaging, potentially for a wide variety of diseases. However, such an AIE system needs to be further developed. In this work, a series of novel cationic AIEgens that are comprised of tricyclic 2-aminopyridinium derivatives with seven-membered rings are designed and synthesized via a simple, multicomponent reaction. Notably, these AIEgens exhibit the ability to specifically stain gram-positive bacteria. Moreover, a specific AIEgen, BMTAP-7, possesses highly efficient bacteriostatic ability for Staphylococcus aureus (S. aureus) in both liquid medium and solid agar plates, which have a minimum inhibitory concentration (MIC) between 4 and 8 µg mL^-1 . Using live-cell imaging and a wash-free process, it is observed that hydrophilic AIEgens are localized to mitochondria, whereas lipophilic AIEgens display specific staining of lysosomes. These AIEgens with bacteriostatic activity hold great promise for distinguishing between bacterial types and inhibiting bacterial infections in situ.

Chloride-promoted self-assembly and photoluminescence of naphthalene diimides tethered to polyacetylene

A novel polyacetylene containing naphthalene diimides (NDIs) in the side chains is sensitive to Cl̄ by structural transformation of the polymer backbone and the NDI aggregates along with turning fluorescence emission on.