Viologen-Cucurbit[7]uril Based Polyrotaxanated Covalent Organic Networks: A Metal Free Electrocatalyst for Oxygen Evolution Reaction.

Viologen-based covalent organic networks represent a burgeoning class of materials distinguished by their captivating properties. Here, supramolecular chemistry is harnessed to fabricate polyrotaxanated ionic covalent organic polymers (iCOP) through a Schiff-base condensation reaction under solvothermal conditions. The reaction between 1,1'-bis(4-aminophenyl)-[4,4'-bipyridine]-1,1'-diium dichloride (DPV-NH2) and 1,3,5-triformylphloroglucinol (TPG) in various solvents yields an iCOP-1 and iCOP-2. Likewise, employing cucurbit[7]uril (CB[7]) in the reaction yielded polyrotaxanated iCOPs, denoted as iCOP-CB[7]-1 and iCOP-CB[7]-2. All four iCOPs exhibit exceptional stability under the acidic and basic conditions. iCOP-CB[7]-2 displays outstanding electrocatalytic Oxygen Evolution Reaction (OER) performance, demanding an overpotential of 296 and 332 mV at 10 and 20 mA cm-2, respectively. Moreover, the CB[7] integrated iCOP-2 exhibits a long-term stable nature for 30 h in 1 m KOH environment. Further, intrinsic activity studies like TOF show a 4.2-fold increase in generation of oxygen (O2) molecules than the bare iCOP-2. Also, it is found that iCOP-CB[7]-2 exhibits a high specific (19.48 mA cm-2) and mass activity (76.74 mA mg-1) at 1.59 V versus RHE. Operando-EIS study evident that iCOP-CB[7]-2 commences OER at a relatively low applied potential of 1.5 V versus RHE. These findings pave the way for a novel approach to synthesizing various mechanically interlocked molecules through straightforward solvothermal conditions.

An Overview of Metal-Organic Framework Based Electrocatalysts: Design and Synthesis for Electrochemical Hydrogen Evolution, Oxygen Evolution, and Carbon Dioxide Reduction Reactions.

Due to the increasing global energy demands, scarce fossil fuel supplies, and environmental issues, the pursued goals of energy technologies are being sustainable, more efficient, accessible, and produce near zero greenhouse gas emissions. Electrochemical water splitting is considered as a highly viable and eco-friendly energy technology. Further, electrochemical carbon dioxide (CO2 ) reduction reaction (CO2 RR) is a cleaner strategy for CO2 utilization and conversion to stable energy (fuels). One of the critical issues in these cleaner technologies is the development of efficient and economical electrocatalyst. Among various materials, metal-organic frameworks (MOFs) are becoming increasingly popular because of their structural tunability, such as pre- and post- synthetic modifications, flexibility in ligand design and its functional groups, and incorporation of different metal nodes, that allows for the design of suitable MOFs with desired quality required for each process. In this review, the design of MOF was discussed for specific process together with different synthetic methods and their effects on the MOF properties. The MOFs as electrocatalysts were highlighted with their performances from the aspects of hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and electrochemical CO2 RR. Finally, the challenges and opportunities in this field are discussed.

Ultrasensitive detection of SARS-CoV-2 S protein with aptamers biosensor based on surface-enhanced Raman scattering.

A rapid and accurate diagnostic modality is essential to prevent the spread of SARS-CoV-2. In this study, we proposed a SARS-CoV-2 detection sensor based on surface-enhanced Raman scattering (SERS) to achieve rapid and ultrasensitive detection. The sensor utilized spike protein deoxyribonucleic acid aptamers with strong affinity as the recognition entity to achieve high specificity. The spherical cocktail aptamers-gold nanoparticles (SCAP) SERS substrate was used as the base and Au nanoparticles modified with the Raman reporter molecule that resonates with the excitation light and spike protein aptamers were used as the SERS nanoprobe. The SCAP substrate and SERS nanoprobes were used to target and capture the SARS-CoV-2 S protein to form a sandwich structure on the Au film substrate, which can generate ultra-strong "hot spots" to achieve ultrasensitive detection. Analysis of SARS-CoV-2 S protein was performed by monitoring changes in SERS peak intensity on a SCAP SERS substrate-based detection platform. This assay detects S protein with a LOD of less than 0.7 fg mL-1 and pseudovirus as low as 0.8 TU mL-1 in about 12 min. The results of the simulated oropharyngeal swab system in this study indicated the possibility of it being used for clinical detection, providing a potential option for rapid and accurate diagnosis and more effective control of SARS-CoV-2 transmission.

A combined experimental and computational investigation on pyrene based D-π-A dyes.

The geometry (twist vs. planar) of a dye is one of the most pivotal factors for determining intramolecular charge transfer (ICT), light harvesting and photovoltaic properties of dye-sensitized solar cells. In order to comprehend the role of dye geometry on the above properties, we have devised the pyrene based D-π-A dyes namely 2-cyano-3-(5-pyren-1-yl-furan-2-yl)-acrylic acid (PFCC) and 2-cyano-3-(5-pyren-1-ylethynyl-furan-2-yl)-acrylic acid (PEFCC). The synthesized pyrene dyes were well characterized by NMR and EI-MS spectrometry. In both the dyes, the donor (pyrene) and acceptor (cyanoacrylic acid) segments remained the same. The varied π-spacers were furan and ethynyl furan. The influences of the ethynyl spacer on the energy levels, light absorption, dynamics of excited states and photovoltaic properties of the DSCs were systematically investigated via theoretical calculations and spectroscopic measurements. UV-visible absorption spectral measurements indicated that the introduction of the ethynyl spacer enhances the molar absorptivity of a dye (PEFCC) in the order of 2, but does not shift the absorption range, which is consistent with the results obtained from density functional theory (DFT) calculations. The theoretical analysis indicated that the charge transfer transition is mainly constituted of the HOMO to the LUMO that were found to be located on donor and acceptor segments, respectively, which is supportive for efficient charge separation and electron injection processes. TDDFT calculations highlighted that the LUMO of the PEFCC dye is more stabilized by the incorporation of the ethynyl group between the pyrene and furan moieties that aid to inject electrons efficiently into TiO2 thereby resulting in an enhanced power conversion efficiency of 2.47% when compared to the PFCC dye. Notably, the overall conversion efficiency of the PEFCC dye reached 60% with respect to that of an N719-based device (4.12%) fabricated under similar conditions. Transient absorption kinetic studies demonstrated that a slower charge recombination rate is an essential factor behind enhanced efficiencies in PEFCC based cells.

Evaluation of the complexation behaviour among functionalized diphenyl viologens and cucurbit[7] and [8]urils.

The complexation behaviour of Diphenyl viologens (DPVs) with Cucurbit[n]urils (CB[n]) was evaluated in detail and the results were reported. In this work, we present the synthesis of various DPVs functionalised with electron withdrawing and electron donating groups (EWGs & EDGs) and investigate their complexation behaviour with CB[7] and CB [8]. Carboxylic acid functionalized DPV's (DPV-COOH) complexation with CB[8] gives additional insights, i.e., indicates hydrogen bonding plays an effective role in the complexation. The formation of a 2:2 quaternary complex of DPV-COOH/CB[8] under neutral pH conditions was supported by various analytical techniques. The complexation of DPVs with CB[7] specifies that irrespective of the functional group attached, they all form a 1:2 ternary complex, but the findings elaborate that the pattern followed in the complexation depends on the EW or EDG attached to the DPVs. The competition experiments conducted between functionalized DPVs and CB[7], CB[8] shows that they have more affinity towards CB[8] than CB[7] because of the better macrocyclic confinement effect of CB[8], as confirmed using UV-Vis spectroscopy. The binding affinity among EWG and EDG functionalised DPVs with CB[8] concludes EDG functionalised DPVs show better affinity towards CB[8], because they can form a charge transfer complex inside the CB[8] cavity. Exploring these host-guest interactions in more complex biological or environmental settings and studying their impact on the functionality of DPVs could be an exciting avenue for future research.

Metal-Ion/Metal Nanoparticle-Anchored Porous Organic Polymers as Efficient Catalysts for Organic Transformations - A Recent Overview.

Porous organic polymers are porous materials that are interlinked with organic building blocks by strong covalent bonds. The functional groups on the building blocks can be carefully chosen to obtain a POP with desired functionalities. In certain cases, the pores or voids interact with the organic molecules via non-covalent interactions and hence they serve as catalytic centers. In many cases, pristine POPs themselves were evaluated as heterogeneous catalysts for their catalytic activity. The inner functional groups of POPs act as a ligand or interact with metal ions/metal nanoparticles and hence a wide range of metal-ion-anchored POPs or metal nanoparticle-loaded POPs were reported. These metal-ion-anchored POPs can catalyze different organic reactions as that of pristine metal-based catalysis following a heterogeneous pathway. In this type of catalysis, POP plays an important role, i. e., it serves as a carbon matrix, and interacts with organic molecules via non-covalent interactions, further in metal/metal-ion-anchored POPs, the metal concentration is highly reduced and the organic transformation effectively takes place at the interface of metal/carbon matrix. Herein, we discuss the recent developments on metal-ion/metal nanoparticle loaded POPs and their role in various organic transformations such as C-C coupling reactions, borrowing hydrogen reactions, CO2 transformations, hydroformylations reactions, oxidation of alkynes to 1,2-diketones and C-H arylation reactions.

Development of robust noble-metal free lanthanum, neodymium doped Li1.05Ni0.5Mn1.5O4 as a bifunctional electrocatalyst for electrochemical water splitting.

Catalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are at the heart of water oxidation reactions. Despite continuous efforts, the development of OER/HER electrocatalysts with high activity at low cost remains a big challenge. Herein, we report a composite material consisting of Li1.05Ni0.5Mn1.5O4, Li1.05Ni0.5 La0.10Mn1.40O4, and Li1.05Ni0.5 Nd0.10Mn1.40O4 as a bifunctional electrocatalyst for OER and HER applications. Though the catalyst has a modest activity for HER, it exhibits high OER activity thereby making it a better nonprecious electrocatalyst for both OER and HER. The catalytic activity arises from the synergetic effects between LNM-La and LNM-Nd by a facile route that shows excellent and durable bifunctional catalytic activity for OER and HER in the alkaline medium developed. The LNM, LNM-La, and, LNM-Nd displayed current densities of 2.17 V, 1.68 V, and 1.93 V vs. RHE at 10 mA cm-2 respectively. The Tafel slope values obtained for LNM, LNM-La, and LNM-Nd are about 419 mV dec-1, 118 mV dec-1, and 378 mV dec-1 respectively. These results indicate the superior electrocatalytic activity of LNM-La with facile OER kinetics.

Enhanced Electrochemical Performance of Hybrid Solid Polymer Electrolytes Encompassing Viologen for All-Solid-State Lithium Polymer Batteries.

Hybrid solid polymer electrolytes (HSPE) comprising poly(ethylene oxide) (PEO), LiTFSI, barium titanate (BaTiO3), and viologen are prepared by a facile hot press. The physical properties of the HSPE membranes are studied by using small-angle and wide-angle X-ray scattering, thermogravimetric analysis, differential scanning calorimetry, and tensile strength. The prepared hybrid solid polymer electrolytes are also investigated by means of ionic conductivity and transport number measurements. The employed analyses collectively reveal that each additive in the PEO host contributes to a specific property: LiTFSI is essential in providing ionic species, while BaTiO3 and viologen enhance the thermal stability, ionic conductivity, and transport number. The enhanced value in the Li+-transport number of HSPE are presumably attributed to the electrostatic attraction of TFSI anions and the positive charges of viologen. Synergistically, the added BaTiO3 and viologen improve the electrochemical properties of HSPE for the applications in all-solid-state-lithium polymer batteries.

A review on biopolymer-derived electrospun nanofibers for biomedical and antiviral applications.

The unique aspects of polymer-derived nanofibers provide significant potential in the areas of biomedical and health care applications. Much research has demonstrated several plausible nanofibers to overcome the modern-day challenges in the field of medical and healthcare. The present review highlights the electrochemical-based nanofibre technologies, special properties of such nanofibres, fabrication strategies (by the electrospinning technique), and their usage in biomedical and healthcare applications. Also, it summarizes the current research on nanofibers as pharmaceutical agents and sustained drug release, tissue-engineered scaffolds, wound healing dressing materials, and antiviral healthcare units like masks, respirators, and personal protective equipment (PPE kits). Attention is given to exclusive sorts of ultrafine fibers (e.g. mesoporous, hollow, core-shell nanofibers) fabricated from various biopolymers and their achievable biomedical applications.

Non-noble metal (Ni, Cu)-carbon composite derived from porous organic polymers for high-performance seawater electrolysis.

The hydrothermal preparation of o-dianisidine and triazine interlinked porous organic polymer and its successive derivatisation via metal infusion (Ni, Cu) under hydrothermal and calcination conditions (700 °C) to yield pristine (ANIPOP-700) and Ni/Cu decorated porous carbon are described here (Ni-ANIPOP-700 and Cu-ANIPOP-700). To confirm their chemical and morphological properties, the as-prepared materials were methodically analyzed using solid state 13C and 15N NMR, X-ray diffraction, Raman spectroscopy, field emission scanning and high resolution transmission electron microscopic techniques, and x-ray photoelectron spectroscopy. Furthermore, the electrocatalytic activities of these electrocatalysts were thoroughly investigated under standard oxygen evolution (OER) and hydrogen evolution reaction (HER) conditions. The results show that all of the materials demonstrated significant activity in water splitting as well as displayed excellent stability (22 h) in both acidic (HER) and basic conditions (OER). Among the electrocatalysts reported in this study, Ni-ANIPOP-700 exhibited a lower overpotential η10 of 300 mV in basic medium (OER) and 150 mV in acidic medium (HER), as well as a lower Tafel slope of 69 mV/dec (OER) and 181 mV/dec (HER), indicating 30% lower energy requirement for overall water splitting. Gas chromatography was used to examine the electrolyzed products.

2D Trimetal-organic framework derived metal carbon hybrid catalyst for urea electro-oxidation and 4-nitrophenol reduction.

Because of the abundance of transition metals, their enhanced electrochemical/chemical efficiency on par with the benchmark catalysts, long-term stability, etc., the expansion of transition metal/metal oxide-based electrocatalysts for oxygen evolution, urea oxidation reactions and 4-nitrophenol reduction becomes indispensable. In particular, the abundant availability along with improved electrochemical performance is crucial for fuel cell applications when it comes to large scale commercialization. In this work, we report the synthesis of a trimetallic metal-organic framework based on Ni, Co and Zn using BTC as a linker and the preparation of its metal oxide - carbon composites at different temperatures, 600, 700 and 800 °C (TM-MOF-600, TM-MOF-700, and TM-MOF-800) by carbonization under an inert atmosphere. The PXRD pattern of TM-MOF complemented well with the simulated XRD patterns of Co-Ni-BTC MOF as well as Zn-BTC MOF, whereas the PXRD pattern of the carbonized samples indicated the presence of three types of metal oxides i.e., CoO, NiO, and ZnO. TEM indicated spherical morphology of TM-MOF, upon calcination, an irregular agglomeration occurred and the average particle size was found to be 60-110 nm. The as-prepared TM-MOF and its carbon composites were tested for their electrocatalytic as well as catalytic activities towards oxygen evolution, urea oxidation and 4-nitrophenol reduction reactions. Electrochemical results indicate the better performance of TM-MOF-800 in both OER and UOR reactions with an onset potential of 1.66 V (OER) and 1.37 V (UOR) at a current density of 10 mA cm-2. The long-term stability of these catalysts under alkaline conditions indicates excellent stability. Besides, the urea electrolyzed products were analyzed by gas chromatography to get clear insights on the formed products. Catalytic reduction of 4-nitrophenol in the presence of excess NaBH4 showed excellent conversion to 4-amino phenol in short duration.

Pore size and surface charge control in mesoporous TiO(2) using post-grafted SAMs.

Two types of TiO(2) are used as mesoporous scaffolds, one (i) randomly sintered yielding an average pore size of 15-20 nm including bottlenecks of 1-3 nm (s-TiO(2)), the other (ii) prepared by evaporation-induced self-assembly with a pore size of 7-9 nm (t-TiO(2)). The pore walls of these materials were post-grafted with phosphonic acids bearing one or two pyridinium or sulfonate head groups via 6, 10 or 14 methylene groups, in order to tune the free pore diameter and the surface charge over a broad range. The modification was characterized by FTIR spectroscopy. Charge transport through the modified pores was investigated by cyclic voltammetry using [Fe(CN)(6)](4-/3-), [IrCl(6)](2-/3-) [Ru(NH(3))(6)](3+/2+), and (ferrocenylmethyl)trimethylammonium as electroactive tracer ions and La(3+) or naphthalene trisulfonate as non-electroactive species. The Faradaic current through the pores is controlled by the combination of surface charge, tracer ion charge, charge of the non-electroactive ions present, as well as the pore diameter. High currents due to strong preconcentration are observed, e.g. a partitioning coefficient value of 7 x 10(3) for [Fe(CN)(6)](4-/3-) on a modified electrode making it a candidate for ion-exchange voltammetry. Other phenomena presented are: (i) electrostatic closure of the porous system due to overlapping Debye layers, (ii) charge inversion of the pore walls, and (iii) the mode of charge propagation along the pore walls. Interestingly s-TiO(2) is more effective at building up an electrostatic barrier compared to t-TiO(2), probably because of narrow bottlenecks which interconnect the pores in s-TiO(2) only.

A review on chemical and electrochemical methodologies for the sensing of biogenic amines.

Biogenic amines (BA) are biomolecules of low molecular weight with organic basic functionalities (amine group) that are formed by the microbial decarboxylation of amino acids of fermented food/beverages. Hence BAs are an important indicator in estimating the freshness and quality of meat, seafood, and industrial food products with high protein content. The reaction of BAs with nitrites available in certain meat products forms nitrosoamine, a carcinogenic compound. Hence BAs are in general considered to be a food hazard and monitoring the level of BAs in food samples becomes crucial as their high concentrations may lead to health problems. This review offers an overview of the available chemical and electrochemical methods that are typically used for the sensing of BAs in food samples. Certain compounds are known to selectively interact with BAs via chemical or non-covalent interactions and these interactions are often accompanied by fluorescence or visible color changes (sometimes visual detection) that could be monitored/assessed using a fluorescence spectrophotometer or UV-vis spectrophotometer (colorimetric methods). The colorimetric methods are limited by sensitivity and selectivity as they are based on straight-forward chemical reactions. In the case of electrochemical sensing of BAs, mediators are often used which undergo oxidation/reduction to produce intermediates that could interact with BAs accompanied by changes in their electrochemical potential. Overall, this review summarizes the available chemical and electrochemical strategies towards the sensing of BAs with a discussion on further prospects.

Observation of inhomogeneous plasmonic field distribution in a nanocavity.

The progress of plasmon-based technologies relies on an understanding of the properties of the enhanced electromagnetic fields generated by the coupling nanostrucutres1-6. Plasmon-enhanced applications include advanced spectroscopies7-10, optomechanics11, optomagnetics12 and biosensing13-17. However, precise determination of plasmon field intensity distribution within a nanogap remains challenging. Here, we demonstrate a molecular ruler made from a set of viologen-based, self-assembly monolayers with which we precisely measures field distribution within a plasmon nanocavity with ~2-Å spatial resolution. We observed an unusually large plasmon field intensity inhomogeneity that we attribute to the formation of a plasmonic comb in the nanocavity. As a consequence, we posit that the generally adopted continuous media approximation for molecular monolayers should be used carefully.

Charge-Discharge and Interfacial Properties of Ionic Liquid-Added Hybrid Electrolytes for Lithium-Sulfur Batteries.

Even though lithium-sulfur batteries possess higher theoretical capacity and energy density than conventional lithium-ion batteries, the challenging issues such as poor electronic conductivity of sulfur, dendrite formation and subsequent polysulfide shuttling, and the undesirable interfacial properties of the lithium metal anode with an electrolyte impede this system from commercialization. To circumvent the dissolution of lithium polysulfides and to improve the interfacial properties of the electrolyte with the lithium metal anode, numerous tactics have been employed. Therefore, in this work, hybrid electrolytes composed of room-temperature ionic liquids of different cations with the bis(trifluoromethanesulfonyl)imide (TFSI) anion and a nonaqueous liquid electrolyte [1 M LiTFSI in tetraethylene glycol dimethyl ether/1,3-dioxolane 1:1 (v/v)] have been prepared, and their physicoelectrochemical properties were thoroughly investigated. The lithium surface upon cycling was characterized by Raman, Fourier transform infrared, and X-ray photoelectron spectroscopy analyses. The dendrite and shuttle current measurements also indicated the formation of a stable solid electrolyte interphase and lower polysulfide shuttling between the electrodes. Among the systems examined, the hybrid electrolyte composed of 1-methyl-1-propylpyrrolidinium TFSI exhibited appreciable charge-discharge characteristics, better interfacial properties with the lithium metal anode, and increased ionic conductivity which were attributed to the enhanced ion-pair interaction that is present between the 1-methyl-1-propylpyrrolidinium cation and the TFSI anion in the electrolyte which was substantiated by Raman analysis.

Facile Construction of a Supramolecular Organic Framework Using Naphthyl Viologen Guests and CB[8] Host via Charge-Transfer Complexation.

Herein, we report the synthesis of guest-host systems comprising naphthyl-viologen-naphthyl (Np-Vio-Np) and viologen-naphthyl-viologen (Vio-Np-Vio) guest molecules and their subsequent supramolecular polymerization in the presence of a CB[8] host in water. In addition, the guest complexation of ethyl-terminated trimeric viologen (ETV) with Np-Vio-Np and CB[8] was investigated. As a result of supramolecular interactions, 2D supramolecular organic frameworks with high internal periodicity were constructed. 1H NMR studies clearly demonstrated the formation of a host-stabilized charge-transfer complex via folding back (Np-Vio-Np and Vio-Np-Vio) in the presence of CB[8]. In the case of ETV + Np-Vio-Np + CB[8], a large polymeric network was formed as indicated by the NMR titrations. UV-vis and fluorescence studies clearly confirm the formation of an inter/intra molecular CT complex upon complexation with cucurbit[8]uril. The size obtained using the dynamic light scattering (DLS) method pinpoints the formation of larger supramolecular aggregates in the order of µm through host-guest assembly, which is further complemented by FESEM and TEM. SAXS measurements indicate the formation of a 2D supramolecular polymer/polymer aggregate with long-range order.

Electropolymerization of thienyl tethered comonomers and application towards the electrocatalytic reduction of nitrobenzene.

The synthesis of different π-spacered thiophene comonomers via Suzuki cross-coupling in good synthetic yields was accomplished. Potentiodynamic electropolymerization of these precursors on ITO electrode by constant potential electrolysis results in the deposition of thin films of polymers between 0.05 and 0.2 µM. Interestingly, the as synthesized π-conjugated polymers exhibit electrochromic behaviour upon electrochemical oxidation. On the application side, the synthesized electropolymers showed catalytic activity better than glassy carbon towards electrochemical reduction of nitrobenzene.

Porous Organic Polymer-Derived Carbon Composite as a Bimodal Catalyst for Oxygen Evolution Reaction and Nitrophenol Reduction.

Ethylene diamine-based porous organic polymer (EPOP) was synthesized, carbonized at different temperatures, and characterized. The successful formation of the triazine polymer was confirmed by Fourier-transform infrared spectroscopy, 13C, and 15N cross-polarization magic angle spinning solid-state NMR. The two-dimensional layered architecture and graphitic nature of the samples resembled that of nitrogen-doped amorphous carbon, as confirmed by Raman, powder X-ray diffraction, and transmission electron microscopy measurements. The catalytic activity of these materials toward nitrophenol reduction and electrocatalytic activity toward oxygen evolution reaction (OER) were systematically evaluated in detail. Electrocatalytic activity toward oxygen evolution reaction was systematically evaluated by chronoamperometry and linear sweep voltammetry. Results clearly demonstrate that all of these catalysts exhibit good OER activity and excellent stability. Among all catalysts, EPOP-700 showed better OER activity, as reflected by its onset potential and current density, comparable with that of the metal-based OER catalysts and better than that of metal-free catalysts. Further, their catalytic activity toward the reduction of 4-nitrophenol to 4-aminophenol was tested with NaBH4; although all of these catalysts showed good catalytic activity; EPOP-800 displayed better catalytic activity.

Nanostructured Graphene Oxide Dots: Synthesis, Characterization, Photoinduced Electron Transfer Studies, and Detection of Explosives/Biomolecules.

Herein, we report the preparation of graphene oxide dots (GO dots) by fine-tuning the carbonization degree of citric acid. The structure of GO dots was characterized by absorption spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, as well as high-resolution scanning electron microscopy and transmission electron microscopy analyses. The typical particle size of the GO dots was 42 nm. The fluorescent characteristics of the GO dots were analyzed by fluorescence spectroscopy. Once excited at 360 nm, the GO dots were fluorescent in the range of 450-550 nm, which was dependent on the excitation wavelength. Further, GO dots were effectively utilized for multifarious applications such as photoinduced electron transfer and detection of explosives and biomolecules. The emission property of GO dots was competently quenched by viologens, picric acid (PA), and bilirubin (BR). The mechanism of quenching by viologens and explosives/biomolecules was found to be due to photoinduced electron transfer and the internal filter effect, respectively. Intriguingly, the detection minimum of PA is in the nanomolar level. Toward commercialization, the economic test strips have also been introduced for the identification of PA. Furthermore, the GO dots have been applied as an efficient luminescent bioprobe for a selective and perceptive finding of BR.

Reversible 2D Supramolecular Organic Frameworks encompassing Viologen Cation Radicals and CB[8].

Reversible 2D supramolecular organic frameworks encompassing branched viologen architectures and cucurbit[8]uril (CB[8]) were constructed and investigated. UV-vis investigation clearly indicates the formation and intermolecular dimerization of monocation radicals and their encapsulation into the hydrophobic CB[8] cavity which is further complemented by EPR (electron paramagnetic resonance) spectroscopy. Particle size measurements by dynamic light scattering method showed particle sizes in the range of several µm indicating larger aggregates. Zeta potential measurements suggested the instability of these particles and their tendency to form aggregates. TEM (transmission electron microscope) analysis further revealed the formation of supramolecular polymer (monocation radical with cucurbit[8]uril) whose diameter were in the range of several µm as indicated by DLS measurements; however the oxidized form, i.e., the viologen dication with cucurbit[8]uril showed dotted spots in the range of sub nanometer level. The internal periodicities of the supramolecular polymers were analyzed by SAXs (small angle X-ray scattering) measurements. Additionally, we have demonstrated that these supramolecular organic frameworks can be depolymerized by oxidation in air and again can be polymerized (intermolecular radical dimerization) by reduction under inert atmosphere demonstrating that these systems will be of broad interest.