Naphthalene diimides: perspectives and promise

Naphthalene Diimide-Based Polycyclic Conjugated Molecule Composite CoFe2O4 Nanohybrids for Photoacoustic Imaging-Mediated Photo-/Sonic Therapy

The complex and harsh tumor microenvironment imped the efficacy of single-modality tumor therapy. With the advantages of biosafety, organic/inorganic nanohybrids have attracted more and more interest of researchers, and it is critical to investigate the development of highly efficient nanohybrids for multimodality combination therapy of cancers. Herein, a naphthalene diimide-based polycyclic conjugated molecule (NDI-S) is designed and synthesized, which has broader light absorption in the near infrared (NIR) region, outstanding photothermal conversion ability, and excellent photostability. Inorganic CoFe2O4 is synthesized via a solvothermal technique, which can produce much more reactive oxygen species (ROS) as a sonosensitizer when activated by ultrasonic (US). NDI-S and CoFe2O4 are then nanoprecipitated to create the organic/inorganic nanohybrids, NDI-S@CoFe2O4. According to the results of in vitro and in vivo experiments, NDI-S@CoFe2O4 can serve as a multifunctional nanoplatform for multimodal treatment of tumors in combination with photothermal/photodynamic/sonodynamic- therapy under the guidance of photoacoustic imaging, which provides a new vision of the development of organic/inorganic nanohybrids for cancer theranostics.

Aggregation-induced generation of circularly polarized luminescence in naphthaleneimide-based nanostructures with high dissymmetry factor

Extensive efforts have been dedicated towards designing new organic materials that display solid-state fluorescence and possess optical activity, thereby leading to the fabrication of materials emitting circularly polarized light. Existing organic materials usually suffer from two limitations, a low dissymmetry factor (glum) and weak or no fluorescence in the solid state. Herein, we have demonstrated a naphthalene imide-based dyad system that remains fluorescent even in powder form and displays circularly polarized luminescence in its aggregated and solid state with significantly high glum values.

Pathway-dependent supramolecular polymerization by planarity breaking

In controlled supramolecular polymerization, planar π-conjugated scaffolds are commonly used to predictably regulate stacking interactions, with various assembly pathways arising from competing interactions involving side groups. However, the extent to which the nature of the chromophore itself (planar vs. non-planar) affects pathway complexity requires clarification. To address this question, we herein designed a new BOPHY dye 2, where two oppositely oriented BF2 groups induce a disruption of planarity, and compared its supramolecular polymerization in non-polar media with that of a previously reported planar BODIPY 1 bearing identical substituents. The slightly non-planar structure of the BOPHY dye 2, as evident in previously reported X-ray structures, together with the additional out-of-plane BF2 group, allow for more diverse stacking possibilities leading to two fiber-like assemblies (kinetic 2A and thermodynamic 2B), in contrast to the single assembly previously observed for BODIPY 1. The impact of the less rigid, preorganized BOPHY core compared to the planar BODIPY counterpart is also reflected in the stronger tendency of the former to form anisotropic assemblies as a result of more favorable hydrogen bonding arrays. The structural versatility of the BOPHY core ultimately enables two stable packing arrangements: a kinetically controlled antiparallel face-to-face stacking (2A), and a thermodynamically controlled parallel slipped packing (2B) stabilized by (BF2) F⋯H (meso) interactions. Our findings underscore the significance of planarity breaking and out-of-plane substituents on chromophores as design elements in controlled supramolecular polymerization.

Commercializable Naphthalene Diimide Anolytes for Neutral Aqueous Organic Redox Flow Batteries

Neutral aqueous organic redox flow batteries (AORFBs) hold the potential to facilitate the transition of renewable energy sources from auxiliary to primary energy, the commercial production of anolyte materials still suffers from insufficient performance of high-concentration and the high cost of the preparation problem. To overcome these challenges, this study provides a hydrothermal synthesis methodology and introduces the charged functional groups into hydrophobic naphthalene diimide cores, and prepares a series of high-performance naphthalene diimide anolytes. Under the synergistic effect of π-π stacking and H-bonding networks, the naphthalene diimide exhibits excellent structural stability and the highest water solubility (1.85 M for dex-NDI) reported to date. By employing the hydrothermal method, low-cost naphthalene diimides are successfully synthesized on a hundred-gram scale of $0.16 g-1 ($2.43 Ah-1), which is also the lowest price reported to date. The constructed full battery achieves a high electron concentration of 2.4 M, a high capacity of 54.4 Ah L-1, and a power density of 318 mW cm-2 with no significant capacity decay observed during long-duration cycling. These findings provide crucial support for the commercialization of AORFBs and pave the way for revolutionary developments in neutral AORFBs.

The Rise of Bacterial G-Quadruplexes in Current Antimicrobial Discovery

Antimicrobial resistance (AMR) is a silent critical issue that poses several challenges to health systems. While the discovery of novel antibiotics is currently stalled and prevalently focused on chemical variations of the scaffolds of available drugs, novel targets and innovative strategies are urgently needed to face this global threat. In this context, bacterial G-quadruplexes (G4s) are emerging as timely and profitable targets for the design and development of antimicrobial agents. Indeed, they are expressed in regulatory regions of bacterial genomes, and their modulation has been observed to provide antimicrobial effects with translational perspectives in the context of AMR. In this work, we review the current knowledge of bacterial G4s as well as their modulation by small molecules, including tools and techniques suitable for these investigations. Finally, we critically analyze the needs and future directions in the field, with a focus on the development of small molecules as bacterial G4s modulators endowed with remarkable drug-likeness.

Design and Construction of the Uranyl Coordination Polymer with Multifunction Stimulus Response: Fluorescent Sensors for Halide Ions and Photochromism

It can provide ideas for the use of uranium elements in the treatment of spent fuel from nuclear wastewater to explore the application potential of uranium element. Thus, it is necessary to research the structure and properties of a novel uranyl coordination polymer (CP) for uranium recovery and reuse. Herein, we designed and prepared a new uranyl CP U-CMNDI based on UO22+ and H2CMNDI (H2CMNDI = N, N'-bis(carboxymethyl)-1,4,5,8-naphthalenediimide). Structural analysis shows that two uranyl ions are connected by two parallel deprotonated CMNDI ligands to form a discrete uranyl dimer structure. U-CMNDI can act as a potential stimulus-responsive halide ion sensor by a fluorescence "turn on" response in water. The limit of detection for fluoride (F-), bromide (Br-), iodide (I-), and chloride (Cl-) is 5.00, 5.32, 5.49, and 5.73 μM, respectively. The fluorescence "turn on" behavior is based on the photoinduced electron transfer (PET) mechanism between halide ions and electron-deficient NDI cores. In addition, U-CMNDI demonstrates a color response to ultraviolet light, exhibiting reversible photochromic behavior with a notable color change. The color change mechanism can contribute to the PET process and the radical process.

Lone-Pair-π Bond Strength Unveiled by a Combined Experimental and Computational Study

A series of naphthalene-diimide (NDI) and perylene-diimide (PDI) connected bis-N-heterocyclic carbene complexes of iridium(III) have been prepared and fully characterized. The analysis of their NMR spectroscopic features, together with their molecular structures show that these species display lone-pair-π interactions between the chloride ligands of the Ir(III) complex and the heterocycles of the NDI/PDI moieties. The detection of this type of interaction in solution is due to the formation of two atropisomers, which are formed as a result of the restricted rotation about the Ir-Ccarbene bond imposed by the (Cl)lp⋅⋅⋅π interaction. Variable-temperature 1H NMR analysis allowed the determination of the strength of this non-covalent interaction, which lies between ΔH=6.6 and 10 kcal/mol. The computational studies performed fully support the experimental findings.

Naphthalene diimide-Annulated Heterocyclic Acenes: Synthesis, Electrochemical and Semiconductor Properties and their Multifaceted Applications

Acenes and Naphthalene Diimides (NDIs) stand as distinguished classes of organic compounds, each possessing unique and intriguing properties that have garnered significant attention across various scientific disciplines. Acenes, characterized by linearly fused aromatic rings, have captivated researchers due to their diverse electronic structures and promising applications in materials science. On the other hand, NDIs, known for their distinctive electron-accepting properties, exhibit remarkable versatility in fields ranging from organic electronics, supramolecular to spin chemistry. In this review, we navigate through the fascinating realms of both acenes and NDIs before converging our focus on the highly diverse and distinctive subgroup of NDI-annulated heterocyclic acenes. This potentially important subgroup, has emerged as a subject of intense investigation, encapsulating their fascinating synthesis, optical and electrochemical characteristics, and multifaceted applications that span the realms of chemistry, physics, and biology. Through the exploration of their synthetic strategies, unique properties, and diverse applications, this review aims to offer a comprehensive understanding of the pivotal role played by NDI-based heterocyclic acenes in contemporary multidisciplinary research and technological innovation.

Pnictogen bonding in imide derivatives for chiral folding and self-assembly

Pnictogen bonding (PnB) is an attraction interaction that originates from the anisotropic distribution of electron density of pnictogen elements, which however has been rarely found in nitrogen atoms. In this work, for the first time, we unveil the general presence of N-involved PnB in aromatic or aliphatic imide groups and reveal its implications in chiral self-assembly of folding. This long-neglected interaction was consolidated by Cambridge structural database (CSD) searching as well as subsequent computational studies. Though the presence of PnB has limited effects on spectroscopic properties in the solution phase, conformation locking effects are sufficiently expressed in the chiral folding and self-assembly behavior. PnB anchors the chiral conformation to control the emergence and inversion of chiroptical signals, while intramolecular PnB induces the formation of supramolecular tilt chirality. It also enables the chiral folding of imide-containing amino acid or peptide derivatives, which induces the formation of unique secondary structural sequences such as β-sheets. Finally, the effects of PnB in directing folded helical structures were revealed. Examples of cysteine and cystine derivatives containing multiple N⋯O and N⋯S PnBs constitute an α-helix like secondary structure with characteristic circular dichroism. This work discloses the comprehensive existence of imide-involved PnB, illustrates its important role in folding and self-assembly, and sheds light on the rational fabrication of conformation-locked compounds and polymers with controllable chiroptical activities.

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.

Functionalized Phenanthrene Imide-Based Polymers for n-Type Organic Thin-Film Transistors

High-performing n-type polymers are crucial for the advance of organic electronics field, however strong electron-deficient building blocks with optimized physicochemical properties for constructing them are still limited. The imide-functionalized polycyclic aromatic hydrocarbons (PAHs) with extended π-conjugated framework, high electron deficiency and good solubility serve as promising candidates for developing high-performance n-type polymers. Among the PAHs, phenanthrene (PhA) features a well-delocalized aromatic π-system with multiple modifiable active sites . However, the PhA-based imides are seldom studied, mainly attributed to the synthetic challenge. Herein, we report two functionalized PhAs, CPOI and CPCNI, by simultaneously incorporating imide with carbonyl or dicyanomethylene onto PhA. Notably, the dicyanomethylene-modified CPCNI exhibits a well stabilized LUMO energy level (-3.84 eV), attributed to the synergetic inductive effect from imide and cyano groups. Subsequently, based on CPOI and CPCNI, two polymers PCPOI-Tz and PCPCNI-Tz were developed. Applied to organic thin-film transistors, owing to the strong electron-deficiency of CPCNI, polymer PCPCNI-Tz shows an improved electron mobility and largely decreased threshold voltage compared with PCPOI-Tz. This work affords two structurally novel electron-deficient building blocks and highlights the effectiveness of dual functionalization of PhAs with strong electron-withdrawing groups for devising n-type polymers.

Radical-Driven Crystal-Amorphous-Crystal Transition of a Metal-Organic Framework

Self-assembly-based structural transition has been explored for various applications, including molecular machines, sensors, and drug delivery. In this study, we developed new redox-active metal-organic frameworks (MOFs) called DGIST-10 series that comprise π-acidic 1,4,5,8-naphthalenediimide (NDI)-based ligands and Ni2+ ions, aiming to boost ligand-self-assembly-driven structural transition and study the involved mechanism. Notably, during the synthesis of the MOFs, a single-crystal-amorphous-single-crystal structural transition occurred within the MOFs upon radical formation, which was ascribed to the fact that radicals prefer spin-pairing or through-space electron delocalization by π-orbital overlap. The radical-formation-induced structural transitions were further confirmed by the postsynthetic solvothermal treatment of isolated nonradical MOF crystals. Notably, the transient amorphous phase without morphological disintegration was clearly observed, contributing to the seminal structural change of the MOF. We believe that this unprecedented structural transition triggered by the ligand self-assembly magnifies the structural flexibility and diversity of MOFs, which is one of the pivotal aspects of MOFs.

Axially Chiral Organic Semiconductors for Visible-Blind UV-Selective Circularly Polarized Light Detection

Technologies that detect circularly polarized light (CPL), particularly in the UV region, have significant potential for various applications, including bioimaging and optical communication. However, a major challenge in directly sensing CPL arises from the conflicting requirements of planar structures for efficient charge transport and distorted structures for effective interaction with CPL. Here, a novel design of an axially chiral n-type organic semiconductor is presented to surmount the challenge, in which a binaphthyl group results in a high dissymmetry factor at the molecular level, while maintaining excellent electron-transporting characteristics through the naphthalene diimide group. Experimental and computational methods reveal different stacking behaviors in homochiral and heterochiral assemblies, yielding different structures: Nanowires and nanoparticles, respectively. Especially, the homochiral assemblies exhibit effective π-π stacking between naphthalene diimides despite axial chirality. Thus, phototransistors fabricated using enantiomers exhibit a high maximum electron mobility of 0.22 cm2 V-1 s-1 and a detectivity of 3.9 × 1012 Jones, alongside the CPL distinguishing ability with a dissymmetry factor of responsivity of 0.05. Furthermore, the material possesses a wide bandgap, contributing to its excellent visible-blind UV-selective detection. These findings highlight the new strategy for compact CPL detectors, coupled with the demonstration of less-explored n-type and UV region phototransistors.

Dual Function of Naphthalenediimide Supramolecular Photocatalyst with Giant Internal Electric Field for Efficient Hydrogen and Oxygen Evolution

Organic supramolecular photocatalysts have garnered widespread attention due to their adjustable structure and exceptional photocatalytic activity. Herein, a novel bis-dicarboxyphenyl-substituent naphthalenediimide self-assembly supramolecular photocatalyst (SA-NDI-BCOOH) with efficient dual-functional photocatalytic performance is successfully constructed. The large molecular dipole moment and short-range ordered stacking structure of SA-NDI-BCOOH synergistically create a giant internal electric field (IEF), resulting in a remarkable 6.7-fold increase in its charge separation efficiency. Additionally, the tetracarboxylic structure of SA-NDI-BCOOH greatly enhances its hydrophilicity. Thus, SA-NDI-BCOOH demonstrates efficient dual-functional activity for photocatalytic hydrogen and oxygen evolution, with rates of 372.8 and 3.8 µmol h-1 , respectively. Meanwhile, a notable apparent quantum efficiency of 10.86% at 400 nm for hydrogen evolution is achieved, prominently surpassing many reported supramolecular photocatalysts. More importantly, with the help of dual co-catalysts, it exhibits photocatalytic overall water splitting activity with H2 and O2 evolution rates of 3.2 and 1.6 µmol h-1 . Briefly, this work sheds light on enhancing the IEF by controlling the molecular polarity and stacking structure to dramatically improve the photocatalytic performance of supramolecular materials.

Influence of Steric Effects on the Emission Behavior of Pyrene-Based Blue Luminogens

Pyrene-based derivatives have been widely deployed in organic luminescent materials because of their bright fluorescence, high charge carrier mobility, and facile modification. Nevertheless, the fluorescence output of conventional pyrenes is prone to quenching upon aggregation due to extensive intermolecular π-π stacking interactions. To address this issue, a set of new Y-shaped pyrene-containing luminogens are synthesized from a new bromopyrene chemical precursor, 2-hydroxyl-7-tert-butyl-1,3-bromopyrene, where the bromo and hydroxyl groups at the pyrene core can be readily modified to obtain the target products and provide great flexibility in tuning the photophysical performances. When the hydroxy group at the 2-position of pyrene was replaced by a benzyl group, the steric hindrance of the benzyl group not only efficiently inhibits the detrimental intermolecular π-π stacking interactions but also rigidifies the molecular conformation, resulting in a narrow-band blue emission. Moreover, the TPE-containing compounds 2c and 3c possessed characteristic aggregation-induced emission (AIE) properties with fluorescence quantum yields of up to 66% and 38% in the solid state, respectively. Thus, this article has methodically investigated the factors influencing the optical behavior, such as intermolecular interactions, and the steric effects of the substituent group, thereby opening up the potential to develop narrow-band pyrene-based blue emitters for OLED device applications.

Fluorescence-based ratiometric sensors as emerging tools for CN- detection: Chemical structures, sensing mechanisms and applications

Hazardous cyanide anions (CN-) are increasingly threatening the environment and human health due to their widespread use in industry and many other fields. Over the past three decades, a large number of probes have been reported to sensitively and selectively detect this toxic anion, while a rather limited number of ratiometric fluorescent probes have been developed. The ratiometric probes have significant potential in bio-imaging and biomedical applications because of the ability to detect CN- in a quick, convenient and affordable way. In this review, we introduce 42 ratiometric fluorescent probes reported in the past 6 years (2018-2023) for CN- detection. Our description includes the chemical structures, photo-physical properties, CN- sensing mechanisms, solution color changes, limits of detection (LODs) and/or various applications of these chemical probes. This review provides guidelines for design and development of a new ratiometric probe for effective CN- detection.

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.

Probing naphthalene diimide and 3-hydroxypropylphosphate as end-conjugating moieties for improved thrombin binding aptamers: Structural and biological effects

The limitations associated with the in vivo use of the thrombin binding aptamer (TBA or TBA15) have dramatically stimulated the search of suitable chemically modified analogues in order to discover effective and reversible inhibitors of thrombin activity. In this context, we previously proposed cyclic and pseudo-cyclic TBA analogues with improved stability that proved to be more active than the parent aptamer. Herein, we have investigated a novel library of TBA derivatives carrying naphthalene diimide (NDI) moieties at the 3'- or 5'-end. In a subset of the investigated oligonucleotides, additional 3-hydroxypropylphosphate (HPP) groups were introduced at one or both ends of the TBA sequence. Evaluation of the G-quadruplex thermal stability, serum nuclease resistance and in vitro anticoagulant activity of the new TBA analogues allowed rationalizing the effect of these appendages on the activity of the aptamer on the basis of their relative position. Notably, most of the different TBA analogues tested were more potent thrombin inhibitors than unmodified TBA. Particularly, the analogue carrying an NDI group at the 5'-end and an HPP group at the 3'-end, named N-TBA-p, exhibited enhanced G-quadruplex thermal stability (ΔTm + 14° C) and ca. 10-fold improved nuclease resistance in serum compared to the native aptamer. N-TBA-p also induced prolonged and dose-dependent clotting times, showing a ca. 11-fold higher anticoagulant activity compared to unmodified TBA, as determined by spectroscopic methods. Overall, N-TBA-p proved to be in vitro a more efficient thrombin inhibitor than all the best ones previously investigated in our group. Its interesting features, associated with its easy preparation, make it a very promising candidate for future in vivo studies.

Tuning the Catalytic Activity of a Pincer Complex of Rhodium(I) by Supramolecular and Redox Stimuli

We report the rhodium(I) complex [Rh(CNC-NDI)(CO)]+ , in which CNC-NDI refers to a pincer-CNC ligand decorated with a naphthalenediimide moiety. Due to the presence of the planar CNC ligand and the naphthalenediimide moiety, the electronic nature of the complex can be modulated by means of supramolecular and redox stimuli, respectively. The metal complex shows a strong π-π-stacking interaction with coronene. This interaction has an impact on the electron-richness of the metal, as demonstrated by the shifting of the ν(CO) stretching band to a lower frequency. The addition of tetrabutylammonium fluoride facilitates the sequential one- and two-electron reduction of the NDI moiety of the ligand, thus resulting in a situation in which the ligand can increase its electron-donor strength in two levels. The nature of the interaction with the fluoride anion was studied computationally. The catalytic activity of the [Rh(CNC-NDI)(CO)]+ complex was tested in the cycloisomerization of alkynoic acids, where it is observed that the activity of the catalyst can be modulated between four levels of activity, which correspond to i) the use of the unmodified catalyst, ii) catalyst+coronene, iii) catalyst+2 equivalents of fluoride, and iv) catalyst+5 equivalents of fluoride.

Construction of Naphthalene Diimide Derived Nanostructured Cathodes through Self-Assembly for High-Performance Sodium-Organic Batteries

Organic nanostructured electrodes are very attractive for next-generation sodium-ion batteries. Their great advantages in improved electron and ion transport and more exposed redox-active sites would lead to a higher actual capacity and enhanced rate performance. However, facile and cost-effective methods for the fabrication of nanostructured organic electrodes are still highly challenging and very rare. In this work, we utilize a bioinspired self-assembly strategy to fabricate nanostructured cathodes based on a rationally designed N-hydroxy naphthalene imide sodium salt (NDI-ONa) for high-performance sodium-organic batteries. Such a well-organized nanostructure can greatly enhance both ion and electron transport. When used as cathode for sodium-organic batteries, it provides among the best battery performances, such as high capacity (171 mA h g-1 at 0.05 A g-1), excellent rate performance (153 mA h g-1 at 5.0 A g-1), and ultralong cycling life (93% capacity retention after 20000 cycles at 3.0 A g-1). Even at low temperature or without a conductive additive, it can also perform well. It is believed that self-assembly is a very powerful strategy to construct high-performance nanostructured electrodes.

Stable peri-Naphthoisatogens without C2 Protection: Synthesis via Aldrone Condensation, Optical Properties and 1,3-Dipolar Cycloaddition Reaction

peri-Annulation of naphthalane, an important tool for realization of wide range of functional materials, is presently accomplished with limited few functional groups like imide, amide and diamine-derivative (perimidine). To increase the diversity, we have incorporated α-keto aldonitrone as a new functional group, and herein report about five peri-naphthoisatogens (PNTIs) dyes. The synthesis were accomplished using an unusual reaction of aromatic nitro group, which is nucleophilic attack of a C-nucleophile (enol) to the N-atom of nitro group. In five different 5-alkylamino-8-nitro-1-acetylnaphthalenes, intramolecular acid-catalyzed nucleophilic attack of enol moiety to the N-atom of nitro group produced α-keto aldonitrone via addition-elimination mechanism. The PNTIs showed characteristics of 1,3-dipole and reacted with ethyl acrylate to produce isoxazolidine ring, which subsequently converted into aza phenalenone derivative via ring cleavage. Both the PNTI and the corresponding derivative strongly absorb in the visible region, displaying absorption maximum at 551 and 561 nm (in CHCl3 ) respectively. Compared to the popular analogous dye naphthalene monoimides, PNTIs showed bathochromic shift of absorption maximum by more than 100 nm. The emission maximum for the PNTI and its derivative in chloroform were observed at 594 and 635 nm respectively.

Design, Synthesis, and Ultrafast Carrier Dynamics of Core-Substituted Naphthalene Diimide-Based Covalent Organic Frameworks

A series of two-dimensional polyimide covalent organic frameworks (2D COF) based on core-substituted naphthalene diimides (cNDIs) were designed and synthesized with the characteristic of tunable bandgap without global structural changes. Cyclic voltammetry (CV) and DFT calculations indicated that COFcNDI-OEt and COFcNDI-SEt possess higher HOMO/LUMO levels and narrower bandgaps than COFNDI-H. Further investigation indicated that the COF bandgaps are not only related to the electron-donating substituents but also varied with respect to the interlayer distances. Moreover, the femtosecond transient absorption (TA) spectra manifested that the electron donor substituents are beneficial to the charge delocalization in the π-columnar unit, resulting in a longer lifetime of charge recombination, which is one of the pivotal prerequisites for high-performance solar cells and photocatalysis.

A Supramolecular Naphthalene Diimide Radical Anion with Efficient NIR-II Photothermal Conversion for E. coli-Responsive Photothermal Therapy

We report a supramolecular naphthalene diimide (NDI) radical anion with efficient NIR-II photothermal conversion for E. coli-responsive photothermal therapy. The supramolecular radical anion (NDI-2CB[7])⋅- , which is obtained from the E. coli-induced in situ reduction of NDI-2CB[7] neutral complex, formed by the host-guest interaction between an NDI derivative and cucurbit[7]uril (CB[7]), exhibits unexpectedly strong NIR-II absorption and remarkable photothermal conversion capacity in aqueous solution. The NIR-II absorption is caused by the self-assembly of NDI radical anions to form supramolecular dimer radicals in aqueous solution, which is supported by theoretically predicted spectra. The (NDI-2CB[7])⋅- demonstrates excellent NIR-II photothermal antimicrobial activity (>99 %). This work provides a new approach for constructing NIR-II photothermal agents and non-contact treatments for bacterial infections.

Aggregation behaviour of pyrene-based luminescent materials, from molecular design and optical properties to application

Molecular aggregates are self-assembled from multiple molecules via weak intermolecular interactions, and new chemical and physical properties can emerge compared to their individual molecule. With the development of aggregate science, much research has focused on the study of the luminescence behaviour of aggregates rather than single molecules. Pyrene as a classical fluorophore has attracted great attention due to its diverse luminescence behavior depending on the solution state, molecular packing pattern as well as morphology, resulting in wide potential applications. For example, pyrene prefers to emit monomer emission in dilute solution but tends to form a dimer via π-π stacking in the aggregation state, resulting in red-shifted emission with quenched fluorescence and quantum yield. Over the past two decades, much effort has been devoted to developing novel pyrene-based fluorescent molecules and determining the luminescence mechanism for potential applications. Since the concept of "aggregation-induced emission (AIE)" was proposed by Tang et al. in 2001, aggregate science has been established, and the aggregated luminescence behaviour of pyrene-based materials has been extensively investigated. New pyrene-based emitters have been designed and synthesized not only to investigate the relationships between the molecular structure and properties and advanced applications but also to examine the effect of the aggregate morphology on their optical and electronic properties. Indeed, new aggregated pyrene-based molecules have emerged with unique properties, such as circularly polarized luminescence, excellent fluorescence and phosphorescence and electroluminescence, ultra-high mobility, etc. These properties are independent of their molecular constituents and allow for a number of cutting-edge technological applications, such as chemosensors, organic light-emitting diodes, organic field effect transistors, organic solar cells, Li-batteries, etc. Reviews published to-date have mainly concentrated on summarizing the molecular design and multi-functional applications of pyrene-based fluorophores, whereas the aggregation behaviour of pyrene-based luminescent materials has received very little attention. The majority of the multi-functional applications of pyrene molecules are not only closely related to their molecular structures, but also to the packing model they adopt in the aggregated state. In this review, we will summarize the intriguing optoelectronic properties of pyrene-based luminescent materials boosted by aggregation behaviour, and systematically establish the relationship between the molecular structure, aggregation states, and optoelectronic properties. This review will provide a new perspective for understanding the luminescence and electronic transition mechanism of pyrene-based materials and will facilitate further development of pyrene chemistry.

Synthesis, Solvatochromism and Fluorescence Quenching Studies of Naphthalene Diimide Dye by Nano graphene oxide

A naphthalene diimide dye with two side amine arm was prepared. Uv-Vis and fluorescence spectroscopic techniques are used for their photophysical and solvatochromic characteristics in different solvents. The Lippert-Mataga plot for naphthalene diimide demonstrated a negative linear dependence by increasing polarity. Results showed naphthalene diimide is more polar in the ground than in the excited state. A quenching study was conducted for interacting the naphthalene diimide as a fluorophore and graphene oxide as a quencher. Fluorescence quenching-based platforms in nanoscale have been used in sensing systems. Raman, FTIR, Uv-Vis and fluorescence spectroscopic techniques were used to study the quenching mechanism. The results indicated that graphene plays an effective quencher against the naphthalene diimide, with a quenching efficiency 91%. The Stern-Volmer analysis results show a mix of static and dynamic quenching mechanisms. The binding constant of the quencher-fluorophore and the number of binding sites have been reported. Thermodynamic parameters of their interaction were evaluated. The negative values of the Gibbs free energy confirm that the complexation process is spontaneous. Meanwhile, the positive entropy value confirms that the favorable pathway process.

An n-Type Conjugated Oligoelectrolyte Mimics Transmembrane Electron Transport Proteins for Enhanced Microbial Electrosynthesis

Interfacing bacteria as biocatalysts with an electrode provides the basis for emerging bioelectrochemical systems that enable sustainable energy interconversion between electrical and chemical energy. Electron transfer rates at the abiotic-biotic interface are, however, often limited by poor electrical contacts and the intrinsically insulating cell membranes. Herein, we report the first example of an n-type redox-active conjugated oligoelectrolyte, namely COE-NDI, which spontaneously intercalates into cell membranes and mimics the function of endogenous transmembrane electron transport proteins. The incorporation of COE-NDI into Shewanella oneidensis MR-1 cells amplifies current uptake from the electrode by 4-fold, resulting in the enhanced bio-electroreduction of fumarate to succinate. Moreover, COE-NDI can serve as a "protein prosthetic" to rescue current uptake in non-electrogenic knockout mutants.

Ratiometric orange fluorescent and colorimetric highly sensitive imidazolium-bearing naphthoquinolinedione-based probes for CN- sensing in aqueous solutions and bio-samples

The widespread use of cyanide (CN^-) in industry results in contamination of various effluents such as drain, lake, and tap water, an imminent danger to the environment and human health. We prepared naphthoquinolinedione (cyclized; 1-5) and anthracenedione (un-cyclized) probes (6-7) for selective detection of CN^-. The addition of CN^- to the probe solutions (1-5) resulted in a color change from pale green to orange under 365 nm illumination. The nucleophilic addition of CN^- to C2 of the imidazolium ring of the probes is responsible for selective CN^- detection. Among all probes, 1 gave the lowest fluorescence-based LOD of 0.13 pM. In contrast, the un-cyclized probes (6 and 7) were substantially inferior to the cyclized counterparts (1 and 2, respectively) for detecting a trace amount of CN^-. The notably low LOD displayed by probe 1 was maintained in the detection of CN^- in real food samples, human fluids, and human brain cells. This is the first report studying imidazolium-bearing naphthoquinolinedione-based probes for CN^- sensing in 100% water.

Naphthalene Diimide-Functionalized Half-Sandwich Ru(II) Complexes as Mitochondria-Targeted Anticancer and Antimetastatic Agents

In this work, four naphthalene diimide (NDI)-functionalized half-sandwich Ru(II) complexes Ru1-Ru4 bearing the general formula [(η⁶-arene)Ru^II(N^N)Cl]PF₆, where arene = benzene (bn), p-cymene (p-cym), 1,3,5-trimethylbenzene (tmb), and hexamethylbenzene (hmb), have been synthesized and characterized. By introducing the NDI unit into the N,N-chelating ligand of these half-sandwich complexes, the poor luminescent half-sandwich complexes are endowed with excellent emission performance. Besides, modification on the arene ligand of arene-Ru(II) complexes can influence the electron density of the metal center, resulting in great changes in the kinetic properties, catalytic activities in the oxidative conversion of NADH to NAD⁺, and biological activities of these compounds. Particularly, Ru4 exhibits the highest reactivity and the strongest inhibitory activity against the growth of three tested cancer cell lines. Further study revealed that Ru4 can enter cells quickly in an energy-dependent manner and preferentially accumulate in the mitochondria of MDA-MB-231 cells, inducing cell apoptosis via reactive oxygen species overproduction and mitochondrial dysfunction. Significantly, Ru4 can effectively inhibit the cell migration and invasion. Overall, the complexation with NDI and modification on the arene ligand endowed the half-sandwich Ru(II) complexes with improved spectroscopic properties and anticancer activities, highlighting their potential applications for cancer treatment.

NDIPhos as a platform for chiral supramolecular ligands in rhodium-catalyzed enantioselective hydrogenation

Chiral naphthalene diimide ligands (NDIPhos) were exploited in rhodium-catalyzed enantioselective hydrogenation. The key feature of these ligands is their ability to self-assemble via π-π interactions to mimic bidentate ligands, offering a complementary method to traditional supramolecular strategies. This concept was further substantiated by computations with the composite electronic-structure method r²SCAN-3c.

Constructing a Photocatalyst for Selective Oxidation of Benzyl Alcohol to Benzaldehyde by Photo-Fenton-like Catalysis

A photoactive metal-organic framework (MOF), [K(H₂O)][Cu(DPNDI)][Cu(DPNDI)(CH₃CN)(H₂O)] [Cu_1.5(DPNDI)_1.5H_1.5P₂W₁₈O₆₂]·2H₂O (Cu(Ι)W-DPNDI), was prepared by combining a functional photosensitizer N, N'-bis(4-pyridylmethyl)naphthalene diimide (DPNDI), copper(I) ions, and an oxidation catalyst [P₂W₁₈O₆₂]^6- into a single framework via a hydrothermal process. Cu(Ι)W-DPNDI exhibited a stable structure, strong light absorption capacity, a suitable band gap, and photoelectric properties, which provided favorable conditions for photocatalysis. In the confined space, the well-aligned Cu(I) ions and POM polyanions played a synergetic effect in the electron-transfer process and reactive oxygen species generation. By coupling photocatalysis and heterogeneous Fenton-like catalysis, Cu(Ι)W-DPNDI displayed high efficiency for the selective oxidation of aromatic alcohols, with up to >99% selectivity and 75% yield.

UV-vis and ECD spectroelectrochemistry of atropisomeric naphthalenediimide derivative

The UV-vis and ECD spectroelectrochemistry (SEC) of a chiral binaphthalenylamine derivative of the N-butyl naphthalenediimide (NDIB-NH₂) enantiomers were applied to measure UV-vis and ECD spectra of NDIB-NH₂ radicals and dianion formed in the reduction and oxidation processes observed in cyclic voltammetry (CV). The CV curves and EPR spectroelectrochemistry enabled us to establish conditions at which a radical-anion [NDIB-NH₂]̇^.-, a dianion [NDIB-NH₂]^2-, and a radical-cation [NDIB-NH₂]̇^.+ are formed. The DFT restricted open-shell CAM-B3LYP-D3/def2TZVP/PCM calculations demonstrated that in the radical-anion [NDIB-NH₂]̇^.-, spin is spread over the NDI system while in the radical-cation [NDIB-NH₂]̇⁺ it is spread over the aminonaphthalene moiety. The UV-vis spectra of radical-anion and dianion show the most significant changes in the 400-800 nm range. In that range, the ECD spectra varied with the change of electrode potential more than the UV-vis did and enabled the identification of a new ECD band of [NDIB-NH₂]̇^.- at ca. 400 nm hidden in the background in the UV spectra at -1000 mV. A broad structured ECD pattern with a maximum at ca. 530 nm was observed for [NDIB-NH₂]̇^.- (-1000 mV), while a single smooth ECD band of [NDIB-NH₂]^2- was located at 520 nm (-1750 mV). For the first time, an isosbestic point (455 nm) was found in ECD spectroelectrochemical measurements for the radical-cation [NDIB-NH₂]̇^.+ in equilibrium with the NDIB-NH₂ neutral form. The TD-DFT CAM-B3LYP-D3/6-31G** calculations combined with the hybrid (explicit combined with implicit) solvation model fairly well reproduced the UV-vis and ECD SEC of neutral and redox forms of NDIB-NH₂ but the ECD spectrum of [NDIB-NH₂]̇^.+ above 390 nm.

Recent Research Progress of Organic Small-Molecule Semiconductors with High Electron Mobilities

Organic electronics has made great progress in the past decades, which is inseparable from the innovative development of organic electronic devices and the diversity of organic semiconductor materials. It is worth mentioning that both of these great advances are inextricably linked to the development of organic high-performance semiconductor materials, especially the representative n-type organic small-molecule semiconductor materials with high electron mobilities. The n-type organic small molecules have the advantages of simple synthesis process, strong intermolecular stacking, tunable molecular structure, and easy to functionalize structures. Furthermore, the n-type semiconductor is a remarkable and important component for constructing complementary logic circuits and p-n heterojunction structures. Therefore, n-type organic semiconductors play an extremely important role in the field of organic electronic materials and are the basis for the industrialization of organic electronic functional devices. This review focuses on the modification strategies of organic small molecules with high electron mobility at molecular level, and discusses in detail the applications of n-type small-molecule semiconductor materials with high mobility in organic field-effect transistors, organic light-emitting transistors, organic photodetectors, and gas sensors.

Controlling π-π Interactions of Highly Soluble Naphthalene Diimide Derivatives for Neutral pH Aqueous Redox Flow Batteries

Organic redox-active molecules are a promising platform for designing sustainable, cheap, and safe charge carriers for redox flow batteries. However, radical formation during the electron-transfer process causes severe side reactions and reduces cyclability. This problem is mitigated by using naphthalene diimide (NDI) molecules and regulating their π-π interactions. The long-range π-stacking of NDI molecules, which leads to precipitation, is disrupted by tethering four ammonium functionalities, and the solubility approaches 1.5 m in water. The gentle π-π interactions induce clustering and disassembling of the NDI molecules during the two-electron transfer processes. When the radical anion forms, the antiferromagnetic coupling develops tetramer and dimer and nullifies the radical character. In addition, short-range-order NDI clusters at 1 m concentration are not precipitated but inhibit crossover. They are disassembled in the subsequent electron-transfer process, and the negatively charged NDI core strongly interacts with ammonium groups. These behaviors afford excellent RFB performance, demonstrating 98% capacity retention for 500 cycles at 25 mA cm^-2 and 99.5% Coulombic efficiency with 2 m electron storage capacity.

Synthesis and Derivatization of an Isomerized Bithiophene Imide (iBTI) Acceptor with a Controllably Twisted Backbone

A heptagonal isomerized bithiophene imide (iBTI) acceptor has been effectively synthesized on a gram scale. Its series of β-, α',β-, α,α'-, α,α',β-, and α,α',β,β'-substituted derivatives can be obtained by controlling brominated sites. Single-crystal analyses indicate that the torsion angle of the imide backbone depends on the number and rigidity of β-substituted groups. Furthermore, the helical chirality of tetrasubstituted and [7]helicene-like derivatives based on iBTI shows great promise for the construction of chiral semiconductor materials.

Periodic mesoporous organosilicas containing naphthalenediimides as organic sensitizers for sulfadiazine photodegradation

In this work, periodic mesoporous organosilicas (PMO) functionalized with the organic sentisizer naphthalenediimide (NDI) were employed as heterogeneous catalysts for the photodegradation of the antibiotic sulfadiazine (SDZ), taken as a model for contaminants of emerging concern (CECs). The catalysts, designated as PMONDI, were prepared by surfactant-directed co-condensation of the precursor N,N'-bis(3-triethoxysilylpropyl)- 1,4,5,8-naphthalenediimide with tetraethoxysilane. The synthesized PMONDI were characterized using transmission electron microscopy, nitrogen adsorption isotherms and small and large angle x-ray scattering. The performance of PMONDI catalysts in the photodegradation of SDZ was compared to that of TiO₂ nanoparticles impregnated into SBA-15 mesoporous silica (TiO₂/SBA-15), under irradiation with a Hg lamp with a bandpass filter of 320-500 nm. Under optimal conditions, PMONDI degraded 100% of the SDZ in 45 min, while the total degradation of SDZ was achieved only after 150 min with TiO₂/SBA-15. PMONDI also performed better than TiO₂/SBA-15 in reuse tests. The mechanism of photodegradation with PMONDI involves the formation of excited triplet states of NDI (³NDI*) upon irradiation, which can then react with molecular oxygen to form reactive oxygen species, which degrade SDZ. Analysis of the SDZ degradation products indicated two main pathways: (1) hydroxylation of the aniline ring and (2) SO₂ extrusion and rearrangement, followed by oxidation of the aniline ring to nitrobenzene. In conclusion, the great potential of the PMONDI materials as photocatalysts for CECs degradation was demonstrated in this work, encouraging further research on these materials for the degradation of pollutants.

Process Dependent Complexity in Multicomponent Gels

Mixing low molecular weight gelators (LMWGs) can be used to combine favorable properties of the individual components within a multifunctional gel. Such multicomponent systems are complex enough in themselves but the method of combining components is not commonly considered something to influence self-assembly. Herein, two multicomponent systems comprising of a naphthalene-based dipeptide hydrogelator and one of two modified naphthalene diimides (NDIs), one of which forms gels, and the other does not, are investigated. These systems are probed, examining the structures formed and their gel properties (when preparing a solution from either a mixed powder of both components or by mixing pre-formed solutions of each component) using rheology, small angle neutron scattering (SANS), and absorbance spectroscopy. It is found that by altering the method of preparation, it is can either induce self-sorting or co-assembly within the fibers formed that underpin the gel network.

Chiral Naphthalenediimides with High-Efficiency Fluorescence and Circularly Polarized Luminescence in the Solid State for the Application in Organic Optoelectronics

Naphthalenediimides (NDIs) have been extensively studied due to their tunable luminescent properties. However, generally, the monomers or aggregates of non-core substituted NDIs exhibit low fluorescence quantum yields (Φ_FL <10 %) in the solid state, which limit their applications as light-emitting materials and render their chiral species unsuitable for circularly polarized luminescence (CPL). Herein, a series of non-core substituted chiral NDIs that exhibit high luminous efficiencies (Φ_FL up to 56.8 % for racemate and 36.5 % for enantiomer) and a strong CPL behavior in the solid state is reported. These significant improvements are attributed to the unique molecular conformation of the chiral NDIs and the formation of distinctive discrete dimers. The structures of the NDIs were significantly simpler and more accessible than those of other NDIs. The findings evidence that non-core substituted NDIs can exhibit strong fluorescence in the solid state and provide a new pathway to improve photophysical properties of NDIs.

π-Stacks of radical-anionic naphthalenediimides in a metal-organic framework

Radical-ionic metal-organic frameworks (MOFs) have unique optical, magnetic, and electronic properties. These radical ions, forcibly formed by external stimulus-induced redox processes, are structurally unstable and have short radical lifetimes. Here, we report two naphthalenediimide-based (NDI-based) Ca-MOFs: DGIST-6 and DGIST-7. Neutral DGIST-6, which is generated first during solvothermal synthesis, decomposes and is converted into radical-anionic DGIST-7. Cofacial (NDI)₂^•- and (NDI)₂^2- dimers are effectively stabilized in DGIST-7 by electron delocalization and spin-pairing as well as dimethylammonium counter cations in their pores. Single-crystal x-ray diffractometry was used to visualize redox-associated structural transformations, such as changes in centroid-to-centroid distance. Moreover, the unusual rapid reduction of oxidized DGIST-7 into the radical anion upon infrared irradiation results in effective and reproducible photothermal conversion. This study successfully illustrated the strategic use of in situ prepared cofacial ligand dimers in MOFs that facilitate the stabilization of radical ions.

Donor-Acceptor Dyads and Triads Employing Core-Substituted Naphthalene Diimides: A Synthetic and Spectro (Electrochemical) Study

Donor-acceptor dyads and triads comprising core-substituted naphthalene diimide (NDI) chromophores and either phenothiazine or phenoxazine donors are described. Synthesis combined with electrochemical and spectroelectrochemical investigations facilitates characterisation of the various redox states of these molecules, confirming the ability to combine arrays of electron donating and accepting moieties into single species that retain the redox properties of these individual moieties.

Synthesis and Properties of Electron-Deficient and Electron-Rich Redox-Active Ionic π-Systems

There is growing interest towards the design and synthesis of organic redox-active systems, which exist in ionic form. Multi- redox systems entail life-sustaining processes like photosynthesis and cellular respiration. The significant challenge for material scientists is to rationally design complex molecular materials that can store and transfer multiple electrons at low operational potentials and are stable under ambient conditions. Also, important are the designed ionic π-systems that combine efficient electron and ion transport. Here, we discuss the synthesis of ionic π-systems which exist in the closed-shell form. Firstly, different classes of ionic arylenediimides and viologens with different π-linkers are discussed from the synthetic, structural and redox perspective. These ionic π-systems are based on the electron deficient π-scaffolds, and are shown to accumulate upto six electrons. We then discuss electron-rich ionic arylenediimides which can exist in anionic form or zwitterionic form. The anionic electron donors have absorption extending to the near Infrared (NIR) region and can be stabilized in aqueous solution. We also discuss the effect of the electron accumulation on the aromaticity and non-aromaticity of the naphthalene and the imide rings of the naphthalenediimides. We finally discuss in brief, the applications related to the organic mixed ionic-electronic conductors.

Squarephaneic Tetraanhydride: A Conjugated Square-Shaped Cyclophane for the Synthesis of Porous Organic Materials

Aromatic carboxylic anhydrides are ubiquitous building blocks in organic materials chemistry and have received considerable attention in the synthesis of organic semiconductors, pigments, and battery electrode materials. Here we extend the family of aromatic carboxylic anhydrides with a unique new member, a conjugated cyclophane with four anhydride groups. The cyclophane is obtained in a three-step synthesis and can be functionalised efficiently, as shown by the conversion into tetraimides and an octacarboxylate. Crystal structures reveal the high degree of porosity achievable with the new building block. Excellent electrochemical properties and reversible reduction to the tetraanions are shown for the imides; NMR and EPR measurements confirm the global aromaticity of the dianions and evidence the global Baird aromaticity of the tetraanions. Considering the short synthesis and unique properties, we expect widespread use of the new building block in the development of organic materials.

Squarephaneic Tetraanhydride: A Conjugated Square-Shaped Cyclophane for the Synthesis of Porous Organic Materials

Aromatic carboxylic anhydrides are ubiquitous building blocks in organic materials chemistry and have received considerable attention in the synthesis of organic semiconductors, pigments, and battery electrode materials. Here we extend the family of aromatic carboxylic anhydrides with a unique new member, a conjugated cyclophane with four anhydride groups. The cyclophane is obtained in a three-step synthesis and can be functionalised efficiently, as shown by the conversion into tetraimides and an octacarboxylate. Crystal structures reveal the high degree of porosity achievable with the new building block. Excellent electrochemical properties and reversible reduction to the tetraanions are shown for the imides; NMR and EPR measurements confirm the global aromaticity of the dianions and evidence the global Baird aromaticity of the tetraanions. Considering the short synthesis and unique properties, we expect widespread use of the new building block in the development of organic materials.

Impact of the Hydrogen-Bonding Functional Group on Hydrogelation of Amphiphilic Naphthalene-diimide Derivatives and Nonspecific Protein Adsorption

This manuscript reports the effect of hydrogen-bonding functionality on the supramolecular assembly of naphthalene-diimide (NDI)-derived amphiphilic building blocks in water. All the molecules contain a central NDI chromophore, functionalized with a hydrophilic oligo-oxyethylene (OE) wedge in one arm and a phenyl group on the opposite arm. They differ by a single H-bonding functionality, which links the NDI chromophore and the phenyl moiety. The H-bonding functionalities are amide, thioamide, urea, and urethane in NDI-A, NDI-TA, NDI-U, and NDI-UT, respectively. All of these molecules exhibit π-stacking in water, as evident from their distinct UV/vis absorption spectra when compared to that of the monomeric dye in THF. However, among these four, only NDI-A and NDI-TA show hydrogelation, while the other two precipitate out of the medium. The NDI-A hydrogel also exhibits transient stability and leads to a crystalline precipitate within ∼5 h. Only NDI-TA produces stable transparent hydrogel with the entangled fibrillar morphology that is typical for gelators. Both NDI-A and NDI-TA showed a thermoresponsive property with a lower critical solution temperature of about 41-42 °C. Powder XRD studies show a parallel orientation for NDI-A and an antiparallel orientation for NDI-TA. Computational studies support this experimental observation and indicate that the NDI-A assembly is highly stabilized by strong H-bonding among the amide groups and π-stacking interaction in the parallel orientation. On the other hand, due to weak H-bonding among the thioamide groups, the binding energy of the parallelly oriented NDI-TA was significantly lower and the optimized structure was disordered. Instead, its antiparallel orientation was more stable, with criss-cross aligned H-bonding interactions and π-π interactions between adjacent aromatic rings. The NDI-TA hydrogel with less ordered OE chains on the surface showed prominent adsorption of serum protein BSA. In sharp contrast, NDI-A did not exhibit any notable interaction with BSA, as evident from the ITC studies.

A highly contorted push-pull naphthalenediimide dimer and evidence of intramolecular singlet exciton fission

Singlet fission is a process by which two molecular triplet excitons are generated subsequent to the absorption of one photon. Molecules that enable singlet fission have triplet state energy at least half of the bright singlet state energy. This stringent energy criteria have challenged chemists to device new molecular and supramolecular design principles to modulate the singlet-triplet energy gap and build singlet fission systems from a wide range of organic chromophores. Herein, we report for the first time intramolecular singlet fission in the seminal naphthalenediimide (NDI) scaffold constrained in a push-pull cyclophane architecture, while individually the NDI chromophore does not satisfy the energy criterion. The challenging synthesis of this highly contorted push-pull cyclophane is possible from the preorganized pincer-like precursor. The special architecture establishes the shortest co-facial NDI⋯NDI contacts (3.084 Å) realized to date. Using broadband femtosecond transient absorption, we find that the correlated T-T pair forms rapidly within 380 fs of photoexcitation. Electronic structure calculations at the level of state-averaged CASSCF (ne,mo)/XMCQDPT2 support the existence of the multi-excitonic T-T pair state, thereby confirming the first example of singlet exciton fission in a NDI scaffold.

Expanding new chemistry of aza-boracyclophanes with unique dipolar structures, AIE and redox-active open-shell characteristics

π-Conjugated macrocycles involving electron-deficient boron species have received increasing attention due to their intriguing tunable optoelectronic properties. However, most of the reported B(sp²)-doped macrocycles are difficult to modify due to the synthetic challenge, which limits their further applications. Motivated by the research of non-strained hexameric bora- and aza-cyclophanes, we describe a new class of analogues MC-BN5 and MC-ABN5 that contain charge-reversed triarylborane (Ar₃B) units and oligomeric triarylamines (Ar₃N) in the cyclics. As predicted by DFT computations, the unique orientation of the donor-acceptor systems leads to an increased dipole moment compared with highly symmetric macrocycles (M1, M2 and M3), which was experimentally represented by a significant solvatochromic effect with large Stokes shifts up to 12 318 cm^-1. Such a ring-structured design also allows the easy peripheral modification of aza-boracyclophanes with tetraphenylethenyl (TPE) groups, giving rise to a change in the luminescence mechanism from aggregation-caused quenching (ACQ) in MC-BN5 to aggregation-induced emission (AIE) in MC-ABN5. The open-shell characteristics have been chemically enabled and were characterized by UV-Vis-NIR spectroscopy and electron paramagnetic resonance (EPR) for MC-BN5. The present study not only showed new electronic properties, but also could expand the research of B/N doped macrocycles into the future scope of supramolecular chemistry, as demonstrated in the accessible functionalization of ring systems.

Naphthalene Diimide-Based Donor-Acceptor-Donor Small Molecules as Metal-Free Organocatalysts for Photocatalytic CO2 Reaction

The application of organic small molecules as metal-free photocatalysts for light-driven photoreduction of carbon dioxide (CO₂) has seldom been explored. This work developed four naphthalene diimide (NDI)-derived donor-acceptor-donor small molecules with different numbers of thiophene units, namely, NDI-2T, NDI-TT, NDI-4T, and NDI-6T, as metal-free photocatalysts to catalyze the reduction of CO₂ under irradiation with an air mass 1.5G solar simulator at one-sun intensity. The structure-property relationship was investigated by exploring the effects of the electron-donating ability of the donor units on the optical properties, redox potential, electron-hole distribution, and exciton lifetime. NDI-6T exhibited the most red-shifted absorption, longest exciton lifetime, and strongest electron-hole separation. However, the large upshift in oxidation potential because of the elevated electron-donating ability of the hexathiophene unit significantly reduced the driving force for catalyst regeneration, leading to poor catalytic performance. Alternatively, NDI-4T possessed proper redox potentials, reduced charge-transfer resistance, and excellent photocurrent intensity; therefore, it effectively converted CO₂ to a single product of CO in the presence of water as an electron donor without a sacrificial reagent or cocatalyst with a product yield of 168.6 μmol g_cat^-1 24 h^-1, which was considerably higher than those of NDI-TT (111.9 μmol g_cat^-1 24 h^-1), NDI-2T (88.4 μmol g_cat^-1 24 h^-1), and NDI-6T (40.5 μmol g_cat^-1 24 h^-1). This study provides a practical guideline for the molecular design of conjugated organic molecules as promising photocatalysts for CO₂ photoreduction.