We report a nonparallel stacked arrangement of donor–acceptor (D–A) pairs for prolonging the lifetime of photoinduced charge-separated states. Hydrogen–hydrogen steric repulsion in naphthalimide-naphthalene (NIN) dyad destabilizes the planar geometry between the constituent units in solution/ground state. Sterically imposed nonplanar geometry of the dyad allows the access of nonparallel arrangement of the donor and acceptor stacks having triclinic space group in the crystalline state. Antiparallel trajectory of excitons in nonparallel D–A stacks can result in lower probability of geminate charge recombination, upon photoexcitation, thereby resulting in a long-lived charge-separated state. Upon photoexcitation of the NIN dyad, electron transfer from naphthalene to the singlet excited state of naphthalimide moiety results in radical ion pair intermediates that survive >10,000-fold longer in the aggregated state (τcra > 1.2 ns) as compared to that of monomeric dyad (τcrm < 110 fs), monitored using femtosecond transient absorption spectroscopy.

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Lithium ion (Li-ion) cells have gained considerable attention in the past few years as one of the most promising energy storage systems for various applications. Binders, an important component of Li-ion cells, have a crucial effect on the performance of the cells. Considerable efforts have been made recently for the development of cost-effective and environmentally friendly water-based binders for Li-ion cells. However, detailed insight of the aqueous-based binders pertaining to the electrode materials exclusively for Li-ion cells has not been reported yet. This Perspective covers the research and development to date on various classes of organic, polymer-based aqueous binders for various anode and cathode materials, which allows for the replacement of toxic and costly N-methyl-2-pyrrolidone and presents a detailed comparative study of various aqueous binders. The effect of various aqueous binders on different electrode-active materials, especially on electrodes under current development, is also discussed. Furthermore, the impact of the binding agents and the related chemical reactions on the morphology of the electrode, specific capacity, and cycle life is reviewed. This Perspective will surely aid the readers to easily identify and study appropriate aqueous binders for electrode-active materials of their interest.

In recent years, solid-state fluorescent materials have received much attention in diverse fields, such as fluorescent biological labels, sensors, and light-emitting diodes.[1] Many conjugated organic luminophores are highly emissive in dilute solutions, however, when fabricated into thin films, they suffer an aggregation-caused quenching (ACQ) effect, which limits their practical applications.[1] To solve this problem, recently, some organic molecules, which show an intense emission in the aggregated state, whereas they exhibit almost no or weak emission in dilute solutions, were reported. This unique phenomenon is widely researched as aggregation-induced emission (AIE) [2] and aggregation-induced enhanced emission (AIEE).[3] However, the potential utility of this phenomenon has not been explored in macrocycles. On the other hand, molecular sensors for Hg II ions have received considerable attention due to the extremely toxic impact exerted by Hg II on our environment. [4] Many efforts have been made to design various chemosensors specific to Hg II ions.[5] The major challenges involved in the creation of Hg II sensors are lack of selectivity and specificity. Calixphyrins, polypyrrolic macrocycles, are known for the coordination chemistry, [6] but reports on metal-ion sensing are very rare. Herein, we wish to report the AIEE characteristic of a calixbenzophyrin-derivative, M-1, and utilize this novel property for probing Hg II ions both in aqueous solution and in the solid state.The syntheses of calixbenzophyrins are outlined in Scheme 1. The synthetic methodology followed here is basically an acid-catalyzed condensation reaction. Stirring a solution of 1 [7] with pentafluorobenzaldehyde in dichloromethane in the presence of trifluoroacetic acid (TFA) followed by oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) resulted in calix[n]-m-benzo[m]phyrins (n = 2,3,4; m = 4,6,8) in 20 % (M-1), 10 % (M-2), and 5 % (M-3) yield, respectively. All the macrocycles were fully characterized by electronic, FAB-MS, and NMR spectral studies, and the structure of M-1 was finally confirmed by single-crystal Xray-diffraction analysis.[8] All the derivatives are soluble in common organic solvents, but insoluble in water.A solution of M-1 in dilute acetonitrile shows an absorption band at 434 nm, which arises from the p-p* transition of the dipyrrin moiety.[8] The emission spectrum shows a band at 539 nm. We observed an anomalous behavior in the emission spectrum of M-1 upon addition of various percentages of water (0-90 %), upon which the band at 539 nm is intensified with a bathochromic shift to 550 nm (Figure 1, left). Because water is not a good solvent for M-1, addition of water promotes efficient calixphyrin self-aggregation, which enhances the emission; in other words, M-1 is AIEE active. The trajectory of the intensity change suggests that the molecularly dissolved M-1 starts to congregate at a water fraction of 50 % and the population of the aggregate continues to increase as the water fraction increases fr...

The current technologically advancing society requires the development of economically profitable and efficient electrode fabrication routes for lithium ion cells. Binders play an important role in deciding the performance parameters, viz., energy density, rate capability, and cycle life of lithium ion cells. The present review provides a practical guide for the development of aqueous binder based cathodes for lithium ion (Li-ion) cells. In this review, we first discuss the need for aqueous binders in the production of electrodes, particularly for cathodes in Li-ion cells, summarize the challenges in the fabrication of aqueous binder based cathodes, and then highlight the recent developments in aqueous binder based cathodes, targeting to provide a stepping stone for the development of aqueous binder based cathodes with improved sustainability and enhanced electrochemical performance. Aqueous binders for different generations of cathode materials are reviewed in detail with special emphasis given to commercially employed cathode materials.

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The formation of well-defined packing motifs and control of π–π stacking by rationalizing the effects of molecular substitution in π-conjugated organic materials represent a significant challenge in supramolecular design. To explore the influence of the thiazolyl group in the solid state packing and photophysical properties of pyrene, a new class of three regioisomeric bisthiazolylpyrenes (2-2″TP) were designed and synthesized. Single crystal X-ray structure and quantum theory of atoms in molecules analysis revealed the presence of S···π interactions in 2′TP. Hirshfeld analysis showed the γ and β packing motif in 2TP and 2″TP, respectively, due to extensive π–π interactions, observed S···π interactions led to herringbone packing in 2′TP. The diverse packing arrangement of 2-2″TP led to a notable difference in the fluorescence behavior in the crystalline state. 2′TP possessing S···π interaction showed remarkable enhanced emission in the crystalline state compared to the amorphous state, in contrast to 2TP and 2″TP. Our results provide new insight for the rational design and regulation of intermolecular interactions of conjugated heterocyclic aromatics to achieve a diverse degree of orbital overlap between neighboring chromophore units and thereby favorable optoelectronic properties.

Pyrene-based materials possessing one-dimensional cofacial π−π stacked structural motifs with short interplanar distances can have favorable charge transport properties. In this work, we have realized the switching of sandwich herringbone to lamellar/columnar arrangement by introducing α-haloacetyl substituents in pyrene. Density functional theory calculations showed that the subtle difference in the charge distribution induced by the haloacetyl group plays an important role in regulating the cofacial stacking. Single-crystal X-ray structural analyses and quantum theory of atoms in molecules (QTAIM) analyses revealed the role of dihydrogen contacts, halogen interactions, and hydrogen bonding in extending the columnar/lamellar arrangement in three dimensions. Hirshfeld surface analyses showed γ (lamellar) and β (columnar) packing motifs indicating extensive π−π stacking interaction between pyrene units. Detailed structural analysis revealed a gradual decrease in the intermolecular π−π stacking distance (d π−π = 3.39 Å) with increasing the polarizability of halogen atom, a characteristic interplanar distance observed in highly oriented pyrolytic graphite (d π−π = 3.35−3.39 Å).