Sethuraman Sankararaman

Non-aqueous organic redox flow batteries (NAORFBs) suffer from rapid capacity fading mainly due to the crossover of redox-active species across the membrane. Minimizing the crossover of redox-active species through ion exchange membranes remains a complex challenge in NAORFBs. To address the crossover issue, we approached the problem through a molecular size exclusion principle designing a dimer of viologen derivative as an anode material. Coupled with N-hexyl phenothiazine as a catholyte, a static cell was demonstrated, which exhibits an excellent cycling stability (100 cycles) with an average Coulombic efficiency of 90% at 10 mA cm−2 current density.

Graphdiyne, a recent addition to the family of 2D covalent organic nanosheet structures, is known for its structural stability and potential applications in catalysis, sensors, electronics and optoelectronics. The design and synthesis of graphdiyne analogues with well-defined structures and useful applications remains a challenging task for materials chemists. Herein, we report a novel, well-defined 2D nanosheet from a coronene–pyrene hybrid 2D material (COPY), with extended π conjugation through acetylenic linkages. The bulk synthesis of the polymeric network has been realized via Sonogashira coupling of 1,4,7,10-tetrabromocoronene and 1,3,6,8-tetraethynylpyrene. The nanosheet is characterized using HR-SEM, TEM, AFM, FT-IR, Raman, XRD and XPS techniques. Electrostatic potential mapping of COPY reveals complete π electron delocalization over the 2D framework with a relatively high electro-negative potential at the acetylenic linkages. Computational study reveals the high planarity of the structure as a result of C_s point group symmetry and the material has a tunable bandgap with respect to the number of coronene and pyrene rings. Extended conjugation in the material accounts for the significant electrical conductivity (1.16 × 10⁻³ S m⁻¹) that is one order of magnitude higher than that of graphdiyne and comparable to the previously reported pyrediyne (a graphdiyne analogue). The large surface area and porous nature of the material were utilized for oil–water separation by incorporating melamine sponge and cotton fabric. The COPY-incorporated cotton fabric exhibited an oil–water separation efficiency of 95.5%. More importantly, the COPY in the melamine sponge exhibited superhydrophobicity with a contact angle of 154.4°. The oil–water separation efficiency, significant electrical conductivity and superhydrophobicity of the material suggest that COPY can be a valuable candidate in the field of water repellency, anti-corrosion and biosensing.

Symmetrically tetrasubstituted derivatives of COT. Which one is it, 1,2,5,6 (C_2v) or 1,4,5,8 (D₂) substituted?

V-shaped molecules with a cyclooctatetraene (COT) core and rigid acene wings are an interesting class of compounds from the point of view of synthetic challenge and their applications in various fields such as photonics and molecular electronics. A new Diels–Alder diene, namely 3,4,7,8-tetrakis-exo-methylenecycloocta-1,5-diene (1), has been synthesized on a multigram scale by the debromination of 1,4,5,8-tetrakis-bromomethylcycloocta-1,3,5,7-tetraene (2) using either zinc powder or NaI. Compound 1 was used as a Diels–Alder diene with various dienophiles to yield the corresponding double Diels–Alder adducts. The Diels–Alder adducts have a COT core and dihydroaromatic wings which were aromatized with a variety of reagents. The methodology described herein provides a direct and shorter route for the synthesis of COT fused with rigid aromatic wings (V-shaped) compared to the existing iterative multistep synthesis of such compounds.

Prospective high reduction potential cathode materials have been proposed that can be used in non-aqueous redox flow battery applications. A new class of material, 3,6-dibromo-9-(p-tolyl)-9H-carbazole (3) incorporating a carbazole core, showing a very good reversibility is employed as the cathode material and dissolved oxygen in the solvent mixture is used as the anolyte material. Labile positions of the carbazole have been substituted with electron withdrawing groups, which increases the reduction potential of the redox couple. Apart from substituting the labile positions, we have also explored the possible structural modification responsible for stabilizing the cation radical of the carbazole moiety and obtained the reversible behavior thereafter. From this, it is evident that a free radical is stabilized upon delocalization of the charge in the molecule. The mass-transport and redox parameters, diffusion coefficient and heterogeneous electron transfer rate coefficient values are high enough to realize good battery performance. A solvent mixture of acetonitrile and dichloromethane (4 : 1) has been used in this work in order to increase the solubility of electroactive materials in the medium.

Pyrediyne is one of the recent entries to carbon‐based 2D material series with better electronic and charge transport properties compared to graphdiyne. Herein, the preparation of pyrediyne‐based quantum dots (PDYQDs), with tunable emission, from nonluminescent 2D precursor pyrediyne is investigated. As‐prepared PDYQDs are characterized by various microscopic as well as spectroscopic techniques such as high‐resolution transmission electron microscopy, atomic force microscopy, X‐ray diffraction, Fourier‐transform infrared spectroscopy, matrix‐assisted laser desorption/ionization, UV‐visible, and fluorescence spectroscopy. The simple preparatory method and absence of heavy metal or external passivating agents make this pyrene‐containing QDs unique. Moreover, the tunable emission (410–548 nm), notable photoluminescence quantum yield (23%), and negligible cytotoxicity of PDYQDs are explored for bioimaging in MCF7 breast cancer cells. The findings in the present study are encouraging to explore novel carbon‐based QDs from their 2D counterparts to enhance their applications in various biological and optoelectronic devices.

A methodology that involves the Pd-catalyzed direct C(sp2)–H bond carbonylation of the C₂ position of indole has been introduced for the synthesis of indolo[1,2-a]quinoxalin-6(5H)-ones.

Co‐facial stacking can result in aggregation‐caused quenching (ACQ) in conjugated organic luminogens. This study provides an attractive ‘slip‐stack’ self‐assembly approach which can eliminate the occurrence of ACQ. The obtained results from steady‐state and time‐resolved optical studies, along with X‐ray diffraction and computational studies demonstrate aggregation‐induced emission enhancement (AIEE) of a donor‐π‐acceptor based 1,3‐diarylpropynone, namely 1‐(naphthalenyl)‐3‐(pyren‐1‐yl)prop‐2‐yn‐1‐one (PYNAP). Unlike the monomer, which exhibits poor photoluminescence in solution (φ_f=2 % in ACN), the twisted manifold of PYNAP allows the orientation of the molecules in a slip‐stack fashion during the course of aggregation, which not only avoids a direct co‐facial arrangement, but also induces augmented rigidity, leading to restricted intramolecular rotation (RIR) and enhanced emission quantum yield (φ_f=5 % in ACN/H₂O). The aggregation behavior of PYNAP's congener, 1‐phenyl‐3‐(pyren‐1‐yl)prop‐2‐yn‐1‐one (PYPH) reinforces the hypothesis that slip‐stack assembly is a useful strategy for AIEE in polycyclic hydrocarbon luminogens.