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A novel chemoselective [3 + 2] annulation reaction of easily accessible ketoxime acetate with 2-aryl-3-ethoxycarbonyl pyrroline-4,5-dione has been developed for the synthesis of unknown pyrrolo[2,3-b]pyrrole frameworks. This method involves copper-mediated N–O bond cleavage followed by the formation of carbon–carbon and carbon–nitrogen bonds. This operationally simple protocol provides broader functional group compatibility and good yields.

Energy storage using aqueous organic redox flow batteries (ORFBs) is gaining momentum in recent years parallel with the renewable energy industry, principally to store energy from solar, wind and hydro generation. The safety and environmental effects of active materials utilised in aqueous ORFB systems are vital to stay true to the ultimate aim of producing a ‘green’ technology. In this review, we evaluate the ‘greenness’ of the synthetic methodology employed to prepare the anolyte or catholyte active materials which have been developed for aqueous ORBFs using the 12 principles of green chemistry. Some of the most common synthetic strategies that will be discussed involve acid catalysis, catalyst free procedures, and oxidative polymerisation. Additionally, the ‘greenness’ of several key commercial materials with limited synthetic procedures published will be considered.

A novel chemoselective [3 + 2] annulation reaction of easily accessible ketoxime acetate with 2-aryl-3-ethoxycarbonyl pyrroline-4,5-dione has been developed for the synthesis of unknown pyrrolo[2,3

Here, we report a microwave-assisted, one-pot, three-component, 1,3-dipolar cycloaddition reaction to produce highly regioselective and stereoselective bis-spirooxindoles as potential inhibitors against amyloid-β fibrillation. Ease of synthesis, promising anti-amyloidogenic activity, low toxicity, and in vitro blood brain barrier permeability makes these compounds attractive therapeutic leads to treat Alzheimer's disease.

Naphthalene diimides (NDIs) are shown to arrange spontaneously co-facially with cucurbit[8]uril (CB[8]) in an aqueous environment through purely non-covalent interactions. The resultant 2 : 2 supramolecular complex of NDI and CB[8] is highly fluorescent (>30 times more than the constituent NDIs) due to the formation of NDI-NDI excimers within the supramolecular complex.

This review focuses on describing all known synthetic strategies leading to core-annulation of naphthalene diimides (NDIs). Strategies presented involve the formation of four-, five- and six-membered ring annulations bearing different heteroatomic and carbocyclic derivatives, including annulenes. The core-annulation method opens the possibility for obtaining designer molecules with tuneable electronic characteristics such as a reduced energy band gap, and enhanced intermolecular overlap of π-systems that improve electronic coupling between molecules-which is highly desirable for charge transport properties summarised in the final pages for applications in electronic devices such as organic field-effect transistors (OFETs) and organic photovoltaic (OPV) cells. Molecular recognition in pH and fluoride sensing, or as a DNA probe, are some of additional applications of core-annulated NDIs presented here. Additionally, recent advances in core modification of NDIs are presented, opening an entire new chemical avenue to be explored. Finally, the outlook on the future prospect of annulated NDIs in various applications is summarised.

Cancer is the second leading cause of death-1 in 6 deaths globally is due to cancer. Cancer metabolism is a complex and one of the most actively researched area in cancer biology. Metabolic reprogramming in cancer cells entails activities that involve several enzymes and metabolites to convert nutrient into building blocks that alter energy metabolism to fuel rapid cell division. Metabolic dependencies in cancer generate signature metabolites that have key regulatory roles in tumorigenesis. In this minireview, we highlight recent advances in the popular methods ingrained in biochemistry research such as stable and flux isotope analysis, as well as radioisotope labeling, which are valuable in elucidating cancer metabolites. These methods together with analytical tools such as chromatography, nuclear magnetic resonance spectroscopy and mass spectrometry have helped to bring about exploratory work in understanding the role of important as well as obscure metabolites in cancer cells. Information obtained from these analyses significantly contribute in the diagnosis and prognosis of tumors leading to potential therapeutic targets for cancer therapy.

The replacement of the imide oxygen atoms with sulfur atoms in the naphthalene diimide (NDI) framework is an attractive strategy for tuning of the electronic properties of such molecules. Here we report the synthesis and characterization of the full series of six thionated NDI molecules with branched side chains. In order to provide a direct comparison with the unthionated parent molecule, a top-gate, bottom contact geometry is adopted, with work function-modified gold electrodes facilitating electron injection. The highest electron mobility was observed for the S2-cis molecule, with a mobility of 0.20 cm2/Vs compared to 0.068 cm2/Vs for the parent molecule. Mobilities slightly lower than that achieved for the S2-cis molecule were also achieved for the S2-trans and S3 derivatives, with the S1, S4 and S2-cis imide derivatives showing mobilities lower than the parent molecule. The thin film microstructure of these molecules has also been explored using a combination of grazing-incidence wide-angle X-ray scattering and near-edge X-ray absorption fine-structure spectroscopy. The performance and microstructure of thin films deposited either by spin-coating or blade coating are also compared.

Pendent-type polymers are attractive materials which allow the flexibility to introduce various redox active moieties that facilitate rapid ion/electron transport and enable charge storage. Here, we demonstrate naphthalene diimide polymers with polynorbornene backbone having N-phenyl, PNAn5 and N-(4-nitrophenyl), PNNO6. Small changes in the molecular design have led to a significant difference in bulk material and device properties. PNNO6 maintained 80% of its capacity at 1C after 10 cycles in a Li-ion coin cell. PNAn5 displayed exceptionally high charge capacity and rate capability with excellent cyclability, maintaining almost its theoretical capacity at various C-rates throughout 500 cycles.

A library of Sox-pyrrolizidines was rapidly prepared by microwave-assisted, one-pot, three-component, 1,3-dipolar cycloaddition of azomethine ylides from l-proline and isatin, with various β-nitrostyrenes. Nitro-Sox compounds, 4b, 4d and 4e inhibit HEWL amyloid fibril formation by ThT studies with percentages of fluorescence intensity of 55.4, 42.9 and 40.3%, respectively. Further studies with MTT assay, Raman spectroscopy, TEM and molecular docking supported these promising candidates for activity against amyloid misfolding, a phenomenon leading to Alzheimer's disease pathology.

In this work, we report on the thermally induced phase behavior and crystalline structures of a series of solution-processable naphthalene diimide (NDI)-based molecules with alkyl side chains of varying length and branching. Taking advantage of synchrotron-based in situ grazing-incidence wide-angle x-ray scattering, the most kinetically favorable thin film crystalline structures of each molecule at room temperature and at elevated temperatures were resolved. The extracted unit cell parameters of the kinetically favorable crystal structures as a function of temperature were used to quantify the anisotropic thermal expansion coefficients along the three principal crystallographic directions. In particular, it is found that long alkyl side chains can effectively suppress crystalline polymorphism and enhance thermal reversibility. The acquired knowledge regarding the thermally induced phase transitions of thin films based on NDI-based small molecules with varying solubilizing side chains serves as guidance for further molecular design and synthesis of high performance $n$-type small molecules.

The development of brightly emissive compounds is of great research and commercial interest, with established and emerging applications across chemistry, biology, physics, medicine and engineering. Among the many types of molecules available, naphthalene diimides have been widely used for both fundamental photophysical studies and in practical applications that utilise fluorescence as an information readout. The monomeric naphthalene diimide is weakly fluorescent, however through various methods of core-derivatisation, it can be developed to be highly fluorescent and further functionalised to add utility. In this review, we highlight recent advances made in naphthalene diimide chemistry that have led to development of molecules with improved optical properties, and the design strategies utilised to produce bright fluorescence emission as small molecules or in supramolecular architectures.

Dimers and trimers of a fluorenone-appended porphyrin were prepared via Lindsey optimized Sonogashira coupling reaction. The photophysical properties of the oligomers were investigated upon excitation of the fluorenone arms which act as donors. The emission profiles of the covalently linked porphyrins suggest that the diphenylacetylene bonds are vital for efficient intramolecular energy transfer between the porphyrin units. Additionally, higher fluorescence quantum yields were recorded for the oligomers than for the individual units.

Transforming the naphthalene diimide (NDI) core into unusual aromatic systems has large potential for applications in which current NDI-based systems show promise. Treatment of N,N-dialkylNDIs under mild oxidizing conditions with ruthenium(III) chloride and sodium periodate affords the corresponding 1,4-diones in good yield. Interestingly, while aliphatic substituents at the N-imide positions allowed oxidation to take place easily, the presence of neutral, electron-rich or electron-deficient phenyl groups retarded the oxidation process under these reaction conditions. The chemistry of the 1,4-dione is then explored through reduction and condensation reactions. In two examples, reaction of the 1,4-dione with diamines gives an unusual, ring-contracted product 20, which has a high quantum yield. Additionally, the 1,4-dione can be converted into larger heterocycles such as 21 and 22 featuring an isoquinoline core. The 1,4-diones and their products have been investigated by spectroscopy, cyclic voltammetry, theoretical studies, and X-ray crystallography. The results obtained demonstrate the potential of the 1,4-dione to serve as an invaluable precursor for NDI-based research.

Here we study the effect of side chain length and type on the microstructure and organic field-effect transistor (OFET) performance of solution-processed naphthalene diimide (NDI) thin films. Linear side chains with four (C4), five (C5), six (C6), eight (C8) and twelve (C12) carbon atoms are studied along with a branched ethylhexyl (EH) side chain. Interestingly, mobilities of up to ~0.2 cm2/Vs are achieved for short (C4) and long (C12) side chains with linear chains of intermediate length and the branched side chain producing lower mobilities. The observed mobility trends are explained in terms of the competing influence of changes in crystal packing and changes in thin film morphology with changes in side chain length. Shorter side chains produce changes in the lateral stacking of NDI units which promote higher mobility while longer side chains produce solution-processed thin films with higher film quality evidenced by larger domain sizes and lower orientational disorder. Side chain length is also found to strongly modulate the molecular orientation of the NDI core, with high edge-on orientations observed for long chains, and tilted orientations for short chains. Thin film microstructure is investigated using a range of techniques including atomic force microscopy, grazing incidence wide-angle X-ray scattering and near-edge X-ray absorption fine-structure spectroscopy.

It is demonstrated that a naphthalene diimide core disubstituted with triphenylamine can be used as a thermally activated delayed fluorescence emitter in organic light emitting diodes. Detailed spectroscopic studies demonstrated unusual host effects on the photophysical properties of this material. In particular, we were able to deduce recombination pathways and the role of the host and temperature in increasing/decreasing the TADF contribution in overall emission. Furthermore, stemming from these host effects on the geometry of the emitter we discover different local triplet states involved in the TADF mechanism. We elucidate this confusing situation to show that simply measuring low-temperature phosphorescence does not always give the energy of the local triplet involved in TADF. The studies carried out in a non-polar polymer and the OLED host were completed by NIR OLED fabrication showing promising characteristics.

By designing dyes with fluoroalkyl groups, the optical and electronic properties of the alkyl analogue were maintained while dramatically altering the solubility. Dyes, F-TABTA (8) and its masked derivative F-TABTSi (9), that enable them to be deposited under conventional organic solvent and scCO2 conditions, respectively, were developed. In liquid DSSC devices, the fluoroalkyl dye (F-TABTA, 8) performs slightly better than its alkyl analogue (D21L6, 10), and interestingly, it was found that the former device showed better stability over time. Deploying the silyl-masked precursor F-TABTSi (9), this dye was deposited onto TiO2 photoanodes from scCO2 in very short contact times (2.5 h), and ECEs of 7.70% were obtained that exceed the performance of the alkyl dye when deposited by conventional methods.

Symmetrically and dissymmetrically core-substituted amino naphthalene diimides (cNDIs) with water-soluble substituents have been synthesised. The compounds display characteristic steady-state optical properties absorbing and emitting light in the visible part of the electromagnetic spectrum. Time-resolved fluorescence studies reveal long emission lifetimes of ∼10 ns in chloroform, ∼8 ns in methanol and ∼4 ns in water. Suitability for use in biophysical applications is demonstrated by encapsulation into reverse micelles and liposomes. Fluorescence lifetime is shown to indicate cavity size in the reverse micelles and fluorescence correlation spectroscopy measurements of cNDI loaded liposomes successfully determined diffusion coefficients and hydrodynamic radii of the liposomes.

Naphthalene diimides undergo single electron reduction processes either chemically or electrochemically at modest potential to yield the corresponding radical anion in high yield. The diimide radical anion has well-behaved properties, including stability, excellent photophysical behaviour and well-structured EPR signals. These properties, combined with the vast array of functionality now possible on the core represent strong candidates for pragmatic photovoltaic devices. This chapter describes the development of naphthalene diimides in photovoltaic systems supported by a theoretical basis for energy and electron transfer mechanisms.

The synthesis and spectroscopic properties of a dissymmetrically core-extended naphthalene diimides derived from o-phenylenediamine and cyanoethene dithiolate were explored. The push-pull nature of the peripheral substituents allows these naphthalene diimide dyes and their progenitors to display interesting photophysical and electrochemical properties, with the target system acting as a highly reversible and quantitative molecular switch with clear absorption and emission readouts based on chemical oxidation and reduction processes.

Water-soluble naphthalene diimide based fluorescent chemosensor, N1, was designed for Cu2+ recognition. The sensor exhibited significant fluorescence modulation and chromogenic change with high Cu2+ sensitivity and selectivity over interfering metal ions. The sensor was able to efficiently monitor Cu2+ in 100% aqueous buffer solution with a low detection limit of 0.7 ppb which is much lower than the recommended value in drinking water by the United States Environmental Protection Agency (U.S. EPA) and the World Health Organization (WHO). The complex formation of N1 with Cu2+ was found to be 1:1 N1-Cu2+ by Job’s plot analysis. Furthermore, the sensor was highly tolerant to interference from a matrix of real samples such as drinking water and human liver carcinoma cell line.

Two new amino core-substituted naphthalene di- imides (cNDIs) bearing fluorinated side chains have been synthesised. Steady-state and time-resolved fluorescence spectroscopy reveals unprecedented optical properties for the cNDIs with high quantum yields of ~ 0.8 and fluores- cence lifetimes of ~ 13 ns in a range of solvents. These prop- erties are apparent at the level of single molecules, where the compounds also show exceptional photostability under pulsed-laser excitation. Photon emission is remarkably con- sistent with very few long timescale (millisecond or longer) interruptions with molecules regularly undergoing > 10 7 cycles of excitation and emission. Intermittencies owing to triplet-state formation occur on a sub-millisecond timescale with a low yield of 1-2 %, indicating that the presence of the fluorine atoms does not lead to a significant triplet yield through the heavy-atom effect. These properties make the compounds excellent candidates for single-molecule label- ling applications.

Near-edge X-ray absorption fine-structure (NEXAFS) spectroscopy is an important tool for probing the structure of conjugated polymer films used in organic electronic devices. High-performance conjugated polymers are often donor-acceptor co-polymers which feature a repeat unit with multiple functional groups. To facilitate better application of NEXAFS spectroscopy to the study of such materials, improved understanding of the observed NEXAFS spectral features is required. In order to examine how the NEXAFS spectrum of a donor-acceptor co-polymer relates to the properties of the sub-units, a series of naphthalene diimide-thiophene-based co-polymers have been studied where the nature and length of the donor co-monomer has been systematically varied. The spectra of these materials are compared with that of a thiophene homopolymer and naphthalene diimide monomer enabling peak assignment and the influence of inter-unit electronic coupling to be assessed. We find that while it is possible to attribute peaks within the π* manifold as arising primarily due to the naphthalene diimide or thiophene sub-units, very similar dichroism of these peaks is observed indicating that it may not be possible to separately probe the molecular orientation of the separate sub-units with carbon K-edge NEXAFS spectroscopy.

Ten alpha-cyclodextrin [2]-rotaxanes have been prepared with alkane-, stilbene- and azobenzene-based axles, capped through nucleophilic substitution of either 2-chloro-4,6-dimethoxy-1,3,5-triazine or 2,4-dichloro-6-methoxy-1,3,5-triazine in aqueous solution, followed by further substitution of the remaining triazinyl chlorine in some cases when the latter capping reagent was used. In one case the rotaxane is a [c(2)]-daisy chain obtained by double-capping the corresponding hermaphroditic cyclic dimer. One of the rotaxane azobenzene derivatives was shown to undergo photochemically-induced reversible interconversion between its trans- and cis-isomers, causing the cyclodextrin to move back and forth along the axle, and therefore behave as a molecular shuttle. The methodology is therefore shown to constitute a general and versatile approach for the construction of supramolecular species as the basis of photochemical molecular devices.

Cyclodextrin [2]rotaxanes have been prepared by coupling dimethylanilines with dicarboxylic acids using DMT-MM, in aqueous solutions of alpha-cyclodextrin, and the example illustrated shows unusual fluorescence emission and other spectroscopic behavior characteristic of the formation of molecular wires in solution, similar to the fibers observed in the solid state.

We report a new technique whereby dyes can be deposited onto metal oxide surfaces using supercritical carbon dioxide (scCO2) for use in solar cell applications. This process eliminates the need for hazardous organic solvents and waste solvents generated during the dyeing process. The solubility of a perylene anhydride dye in scCO2 is enhanced by the incorporation of fluorinated alkyl subsituents and the use of masked carboxylic binding groups. This allows fast deposition of the dye onto the TiO2 photoanode, resulting in efficient photovoltaic performance. The unreacted dye is then easily recovered in a solid form after the deposition process by venting the carbon dioxide.