Silafluorene‐based polymers for electrochromic and polymer solar cell applications

In this study, four novel silafluorene (SiF) and benzotriazole (Btz) bearing conjugated polymers are synthesized. In the context of electrochemical and optical studies, these polymers are promising materials both for electrochromic device (ECD) and polymer solar cell (PSC) applications. All of the polymers are ambipolar (both p‐ and n‐dopable) and multichromic. Electrochemistry experiments indicate that incorporation of selenophene instead of thiophene unit increases the HOMO energy level of the polymers. Power conversion efficiency of the PSCs reached 1.75% for PTBTSiF, 1.55% for PSBSSiF, 2.57% for PBTBTSiF, and 1.82% for PBSBSSiF. The hole mobilities of the polymers are estimated through space charge limited current (SCLC) model. PBTBTSiF has the highest hole mobility as 2.44 × 10^?3 cm² V s^?1. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1541–1547     

Electrochemical Glucose Biosensors: Whole Cell Microbial and Enzymatic Determination Based on 10-(4H-Dithieno[3,2-b:2′,3′-d]Pyrrol-4-yl)Decan-1-Amine Interfaced Glassy Carbon Electrodes

The fabrication of amperometric biosensors based on whole cell Gluconobacter oxydans DSMZ 2343 (G. oxydans) and glucose oxidase (GOx) was performed for the detection of glucose. Glassy carbon electrodes (GCE) were coated with a 10-(4H-dithiyeno [3,2-b:2’,3’-d]pyroll-4-il)decan-1-amine (DTP-alkyl-NH₂) polymer using an electropolymerization method and the formed interface was used to connect the bacteria and the enzyme to the electrode. The transfer of electrons from enzyme to electrode was successfully demonstrated by the biocatalytic activity and unique morphology of the conducting polymer. Characterization of the biosensors was assessed using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM) analyses. The detection limits of the enzyme and microbial based biosensors for glucose were 0.022 and 0.081?mM, respectively. The broad linear dynamic ranges of the GOx and G. oxydans biosensors were observed to be 0.045–50.0 and 0.19–50.0?mM, respectively. The analytical performances of biosensors were compared according to the following figures of merit: detection limits, limits of quantification, pH and current response time. In addition, to demonstrate the applicability of the biosensors, real-time measurements and recovery studies were evaluated.     

Surface electronic structure transitions at high temperature on perovskite oxides: the case of strained La0.8Sr0.2CoO3 thin films

In-depth probing of the surface electronic structure on solid oxide fuel cell (SOFC) cathodes, considering the effects of high temperature, oxygen pressure, and material strain state, is essential toward advancing our understanding of the oxygen reduction activity on them. Here, we report the surface structure, chemical state, and electronic structure of a model transition metal perovskite oxide system, strained La(0.8)Sr(0.2)CoO(3) (LSC) thin films, as a function of temperature up to 450 °C in oxygen partial pressure of 10(-3) mbar. Both the tensile and the compressively strained LSC film surfaces transition from a semiconducting state with an energy gap of 0.8-1.5 eV at room temperature to a metallic-like state with no energy gap at 200-300 °C, as identified by in situ scanning tunneling spectroscopy. The tensile strained LSC surface exhibits a more enhanced electronic density of states (DOS) near the Fermi level following this transition, indicating a more highly active surface for electron transfer in oxygen reduction. The transition to the metallic-like state and the relatively more enhanced DOS on the tensile strained LSC at elevated temperatures result from the formation of oxygen vacancy defects, as supported by both our X-ray photoelectron spectroscopy measurements and density functional theory calculations. The reversibility of the semiconducting-to-metallic transitions of the electronic structure discovered here, coupled to the strain state and temperature, underscores the necessity of in situ investigations on SOFC cathode material surfaces.     

Structural and Size Effects on the Spectroscopic and Redox Properties of CdSe Nanocrystals in Solution: The Role of Defect States

Two series of CdSe quantum dots (QDs) with different diameters are prepared, according to frequently used protocols of the same synthetic procedure. For each sample the photophysical properties and the potentials for the first reduction and oxidation processes in organic solution are determined. The band gap obtained from electrochemical experiments is compared with that determined from the absorption and luminescence spectra. While the optical band gap decreases upon increasing the nanocrystal diameter, as expected on the basis of quantum confinement, the redox potentials and the electrochemical band gap are not monotonously related to the QD size. For both series, the smallest and largest QDs are both easier to oxidize and reduce than mid‐sized QDs. In fact, the latter samples exhibit very broad voltammetric profiles, which suggests that the heterogeneous electron‐transfer processes from/to the electrode are kinetically hindered. Conversely, the electrochemical band gap for the smallest and largest particles of each series is somewhat smaller than the optical band gap. These results indicate that, while the optical band gap depends on the actual electron–hole recombination within the nanocrystal, and therefore follows the size dependence expected from the particle‐in‐a‐box model, the electrochemical processes of these QDs are strongly affected by other factors, such as the presence of surface defects. The investigations suggest that the influence of these defects on the potential values is more important for the smallest and largest QDs of each series, as confirmed by the respective luminescence bands and quantum yields. An interpretation for the size‐dependent evolution of the surface defects in these nanocrystals is proposed based on the mechanism of their formation and growth.     

An efficient microwave-assisted synthesis of novel quinolone–triazole and conazole–triazole hybrid derivatives as antimicrobial and anticancer agents

1,2,4-Triazole-fluoroquinolone and 1,2,4-triazole–conazole hybrids are designed, synthesized, and investigated in vitro against a variety of common diseases. The structure of the newly synthesized compounds are characterized from spectral data (IR, ¹H NMR, ¹³C NMR, and LC–MS). The antibacterial activity against both Gram-positive and Gram-negative bacteria is shown to be enhanced by many of the produced compounds. Also, some of the products are found to have strong antiproliferative effects aganist HeLa cervical cancer cells, whilst demonstrating cytotoxic effects toward normal cells.     

A Bifunctional Photosensitizer for Enhanced Fractional Photodynamic Therapy: Singlet Oxygen Generation in the Presence and Absence of Light

The photosensitized generation of singlet oxygen within tumor tissues during photodynamic therapy (PDT) is self‐limiting, as the already low oxygen concentrations within tumors is further diminished during the process. In certain applications, to minimize photoinduced hypoxia the light is introduced intermittently (fractional PDT) to allow time for the replenishment of cellular oxygen. This condition extends the time required for effective therapy. Herein, we demonstrated that a photosensitizer with an additional 2‐pyridone module for trapping singlet oxygen would be useful in fractional PDT. Thus, in the light cycle, the endoperoxide of 2‐pyridone is generated along with singlet oxygen. In the dark cycle, the endoperoxide undergoes thermal cycloreversion to produce singlet oxygen, regenerating the 2‐pyridone module. As a result, the photodynamic process can continue in the dark as well as in the light cycles. Cell‐culture studies validated this working principle in vitro.     

Disclosing Cyclic(Alkyl)(Amino)Carbenes as One-Electron Reductants: Synthesis of Acyclic(Amino)(Aryl)Carbene-Based Kekulé Diradicaloids

Herein, we disclose cyclic(alkyl)(amino)carbenes (CAACs) to be one-electron reductants under the formation of a transient radical cation as indicated by EPR spectroscopy. The disclosed CAAC reducing reactivity was used to synthesize acyclic(amino)(aryl)carbene-based Thiele and Chichibabin hydrocarbons, a new class of Kekulé diradicaloids. The results demonstrate CAACs to be potent organic reductants. Notably, the acyclic(amino)(aryl)carbene-based Chichibabin's hydrocarbon shows an appreciable population of the triplet state at room temperature, as evidenced by both variable-temperature NMR and EPR spectroscopy.     

Kinetic investigations of formation of polyimides containing arylene sulfone ether linkages by potentiometric titration and their characterization

In this work, thermal solution imidization kinetics of two high performance polyimides, prepared from the polycondensation of pyromellitic dianhydride (PMDA) and 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) with 4,4′-bis(3-aminophenoxy)diphenylsulfone (DAPDS) were investigated using nonaqueous titration technique with tetramethylammonium hydroxide. Most of the kinetic investigations, found in the literature, are based on the aromatic p-diamines.^1,2 In the present work, attention was focused on imidization kinetics with m-substituted aromatic diamines having electron donating ( O ) and electron withdrawing ( SO₂ ) groups in the same molecule. Kinetic parameters, namely the rate constants, activation energies, entropies and enthalpies of imidization reactions were determined and compared with the literature values. It is reported in literature³ that electron affinities of dianhydrides and ionization potentials of diamines, have strong influence on the reaction rate and activation energies of imidization. Activation energy (E_a) values were found to be 66 and 57 kJ/mol for DAPDS/PMDA and DAPDS/BTDA respectively, and order of reaction was found to be second order. Polyimides DAPDS/PMDA and DAPDS/BTDA, subjected to kinetic investigation, showed glass transition temperatures of 267°C and 241°C, both were found to be thermally stable up to 500°C. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2981–2990, 1997