2,1,3‐benzothiadiazole‐5,6‐dicarboxylicimide based semicrystalline polymers for photovoltaic cells

Two semicrystalline low band gap polymers based on highly electron‐deficient 2,1,3‐benzothiadiazole‐5,6‐dicarboxylicimide (BTI) were synthesized by considering the chain planarity via intrachain noncovalent coulombic interactions. The thiophene‐BTI and thienothiophene‐BTI based PPDTBTI and PPDTTBTI have a low band gap (～1.5 eV) via strong intramolecular charge transfer interaction, showing a broad light absorption covering 300～850 nm. Semicrystalline film morphology was observed for both polymers in the grazing incidence wide angle X‐ray scattering measurements. Interestingly, PPDTBTI showed a pronounced edge on packing structure but PPDTTBTI showed predominantly a face on orientation in both pristine and blend films. Different packing patterns influenced significantly the charge carrier transport, recombination and resulting photovoltaic characteristics. The best power conversion efficiency was measured to be 5.47% for PPDTBTI and 6.78% for PPDTTBTI, by blending with the fullerene derivative, PC₇₁BM. Compared to the PPDTBTI blend, PPDTTBTI: PC₇₁BM suffered from the lower open‐circuit voltage but showed the substantially higher hole mobility and short‐circuit current density with smaller charge recombination, showing very good agreements with molecular structures and morphological characteristics. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3826–3834     

Correlation and network topologies in global and local stock indices

We examined how the correlation and network structure of the global indices and local Korean indices have changed during years 2000–2012. The average correlations of the global indices increased with time, while the local indices showed a decreasing trend except for drastic changes during the crises. A significant change in the network topologies was observed due to the financial crises in both markets. The Jaccard similarities identified the change in the market state due to a crisis in both markets. The dynamic change of the Jaccard index can be used as an indicator of systemic risk or precursors of the crisis.     

Efficient and selective oxidation of alcohols in water employing palladium supported nanomagnetic Fe3O4@hyperbranched polyethylenimine (Fe3O4@HPEI.Pd) as a new organic–inorganic hybrid nanocatalyst

Palladium immobilized magnetic nanoFe₃O₄@hyperbranched polyethylenimine (Fe₃O₄@HPEI.Pd) was prepared according to a simple and cost effective pathway and it was employed as a new efficient and selective organic–inorganic hybrid nanocatalyst for the aqueous oxidation of primary and secondary alcohols to their corresponding products in good yields applying oxone (potassium hydrogen monopersulfate) and H₂O₂ as an oxidant at room temperature. Moreover, the catalytic system was reused at least 13 times without significant loss of activity. The complete characterization of this efficient nanocatalyst was investigated by FTIR, UV–Vis, TEM, SEM, XRD, TGA, VSM, ICP and EDX techniques.     

Nonheme Iron Imido Complexes Bearing a Non-Innocent Ligand: A Synthetic Chameleon Species in Oxidation Reactions

High-valent iron-imido complexes can perform C−H activation and sulfimidation reactions, but are far less studied than the more ubiquitous iron-oxo species. As case studies, we have looked at a recently published iron(V)-imido ligand π-cation radical complex, which is formally an iron(VI)-imido complex [Fe^V(NTs)(TAML^+.)] ( 1 ; NTs=tosylimido), and an iron(V)-imido complex [Fe^V(NTs)(TAML)]⁻ ( 2 ). Using a theoretical approach, we found that they have multiple energetically close-lying electromers, sometimes even without changing spin states, reminiscent of the so-called Compound I in Cytochrome P450. When studying their reactivity theoretically, it is indeed found that their electronic structures may change to perform efficient oxidations, emulating the multi-spin state reactivity in Fe^IVO systems. This is actually in contrast to the known [Fe^V(O)(TAML)]⁻ species ( 3 ), where the reactions occur only on the ground spin state. We also looked into the whole reaction pathway for the C−H bond activation of 1,4-cyclohexadiene by these intermediates to reproduce the experimentally observed products, including steps that usually attract no interest (neither theoretically nor experimentally) due to their non-rate-limiting status and fast reactivity. A new “clustering non-rebound mechanism” is presented for this C−H activation reaction.     

Kinetic study of low‐temperature imidization of poly(amic acid)s and preparation of colorless,transparent polyimide films

Conventional synthesis of polyimides includes high‐temperature (160–350 °C) imidization of poly(amic acid)s. In the present work, imidization has been carried out at much lower temperatures (40–160 °C). 1,2,4,5,‐cyclohexanetetracarboxylic dianhydride (HPMDA) or pyromellitic dianhydride (PMDA) was polymerized with an aromatic diamine, 4,4′‐diaminodiphenylmethane (DDPM), to give poly(amic acid)s, which were then imidized chemically. Imidization was more than 90% complete even at the very low imidization temperature of 40 °C. It was found that the imidization occurs in two steps: an initial rapid cyclization and a subsequent slower cyclization. The activation energy for the rapid process was determined to be 4.3 kJ/mol, and that of the slower process, 4.8 kJ/mol. As the imidization temperature decreases, the transmittance of the resulting polyimides tends to gradually increase, the cutoff wavelength decreases and the color becomes pale. A partially aliphatic polyimide based on HPMDA and DDPM prepared at 40 °C yielded thin films that were highly transparent and colorless, and had good flexibility, solubility and thermal stability. The polyimide films prepared in this study may be good candidates for flexible, transparent plastic substrates in the display industry. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1593–1602     

Formation of activation‐free,selectively bioconjugatable poly(N‐acryloxysuccinimide‐co‐oligoethylene glycol methyl ether methacrylate) films by surface‐initiated ARGET ATRP

Activation‐free copolymeric films possessing high selectivity to target proteins and low biofouling background are prepared via controlled radical polymerization. The copolymeric films are generated by surface‐initiated activators regenerated by electron transfer atom transfer radical polymerization (SI‐ARGET ATRP) of N‐acryloxysuccinimide (NAS) and oligo(ethylene glycol) methyl ether methacrylate (OEGMEMA) by controlling the molar feed ratio of the two monomers. The formation of copolymeric films is characterized by ellipsometry, contact angle goniometry, FTIR spectroscopy, and X‐ray photoelectron spectroscopy. The prepared copolymeric films are biotinylated without an activation step. Biotin–streptavidin association is employed as a model system to investigate both selective binding and the relevant signal‐to‐noise (S/N) ratio. When the molar feed ratio of NAS and OEGMEMA is 2:8, the copolymeric film is optimized to give the highest S/N ratio (339.8) according to surface plasmon resonance studies. The highly selective bioconjugation is used to generate micropatterns of rhodamine‐conjugated streptavidin on the copolymeric film. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 329–337