[1,2,5]thiadiazolo[3,4‐g]quinoxaline acceptor‐based donor–acceptor–donor‐type polymers: Effect of strength and size of donors on the band gap

Electrochromic polymers based on [1,2,5]thiadiazolo[3,4‐g]quinoxaline acceptor and thiophene, 3,4‐ethylenedioxythiophene and 3,3‐didecyl‐3,4‐proylenedioxythiophene donors, namely poly(6,7‐diphenyl‐4,9‐di(thiophen‐2‐yl)‐[1,2,5]thiadiazolo[3,4‐g]quinoxaline) ( P1 ), poly(4‐(2,3‐dihydrothieno[3,4‐b][1,4]dioxin‐5‐yl)‐9‐(2,3‐dihydrothieno[3,4‐b][1,4]dioxin‐7‐yl)‐6,7‐diphenyl‐[1,2,5]thiadiazolo[3,4‐g]quinoxaline) ( P2 ), and poly(4‐(3,3‐didecyl‐3,4‐dihydro‐2H‐thieno[3,4‐b][1,4]dioxepin‐6‐yl)‐9‐(3,3‐didecyl‐3,4‐dihydro‐2H‐thieno[3,4‐b][1,4]dioxepin‐8‐yl)‐6,7‐diphenyl‐[1,2,5]thiadiazolo[3,4‐g]quinoxaline) ( P3 ), respectively, were electrochemically and/or chemically synthesized and characterized. Electrochemical and optical properties of the polymers were then investigated. The results, which were obtained electrochemically and optically, indicate that the polymers bearing the same acceptor and different donor units have a band gap range of 0.59–1.24 eV depending on the strength and size of the donor units and band gap determination method. A significant finding in this study was the phenomenon that when the acceptor is physically huge, the general rule that a weak donor would have a high band gap whereas a strong donor would have low band gap can be broken due to the torsional angles/steric hindrances involved with physically large donor molecules. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3483–3493     

Substituent and heteroatom effects on the electrochromic properties of similar systems

Electrochromic polymers called poly(3,4‐dihydro‐3,3‐bis ((naphthalen‐1‐yl)methyl)‐2H‐thieno[3,4‐b][1,4]dioxepine) (PProDOT‐Np₂), poly(3,3‐dibenzyl‐3,4‐dihydro‐2H‐selenopheno[3,4‐b][1,4]dioxepine), and poly(3,3‐dibenzyl‐3,4‐dihydro‐2H‐thieno[3,4‐b][1,4]dioxepine) were synthesized electrochemically and the effect of substituents and heteroatoms on the electrochromic properties were investigated for the similar systems. All polymers show electrochromism from a colored state when neutralized to transmissive when oxidized. Although, increasing bulky size (PProDOT‐Np₂) causes lower coloration efficiency (CE) as well as lower optical contrast, the replacement of S atom by Se atom resulted in a lower band gap polymer with a higher CE than its thiophene analog. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Critical coupling in plasmonic resonator arrays

We report critical coupling of electromagnetic waves to plasmonic cavity arrays fabricated on Moiré surfaces. Dark field plasmon microscopy imaging and polarization dependent spectroscopic reflection measurements reveal the critical coupling conditions of the cavities. The critical coupling conditions depend on the superperiod of the Moiré surface, which also defines the coupling between the cavities. Complete transfer of the incident power can be achieved for traveling wave plasmonic resonators, which have a relatively short superperiod. When the superperiod of the resonators increases, the coupled resonators become isolated standing wave resonators in which complete transfer of the incident power is not possible. Analytical and finite difference time domain calculations support the experimental observations.     

Fragment growing induces conformational changes in acetylcholine-binding protein: a structural and thermodynamic analysis

Optimization of fragment hits toward high-affinity lead compounds is a crucial aspect of fragment-based drug discovery (FBDD). In the current study, we have successfully optimized a fragment by growing into a ligand-inducible subpocket of the binding site of acetylcholine-binding protein (AChBP). This protein is a soluble homologue of the ligand binding domain (LBD) of Cys-loop receptors. The fragment optimization was monitored with X-ray structures of ligand complexes and systematic thermodynamic analyses using surface plasmon resonance (SPR) biosensor analysis and isothermal titration calorimetry (ITC). Using site-directed mutagenesis and AChBP from different species, we find that specific changes in thermodynamic binding profiles, are indicative of interactions with the ligand-inducible subpocket of AChBP. This study illustrates that thermodynamic analysis provides valuable information on ligand binding modes and is complementary to affinity data when guiding rational structure- and fragment-based discovery approaches.     

The maleimide modified epoxy resins for the preparation of UV‐curable hybrid coatings

In the present study, maleimide‐modified epoxide resin containing UV‐curable hybrid coating materials were prepared and coated on polycarbonate substrates in order to improve their surface properties. UV‐curable, bismaleimide‐modified aliphatic epoxy resin was prepared from N‐(p‐carboxyphenyl) maleimide (p‐CPMI) and cycloaliphatic epoxy (Cyracure‐6107) resin. The structure of the bismaleimide modified aliphatic epoxy resin was analyzed by FTIR and the characteristic absorption band for maleimide ring was clearly observed at 3100 cm^?1. Silica sol was prepared from tetraethylorthosilicate (TEOS) and methacryloxy propyl trimethoxysilane (MAPTMS) by sol–gel method. The coating formulations with different compositions were prepared from UV‐curable bismaleimide‐based epoxy oligomer and sol–gel mixture. The molecular structure of the hybrid coating material was analyzed by ²⁹Si‐CP/MAS NMR spectroscopy techniques. In the ²⁹Si CP/MAS NMR spectrum of the hybrid coating, mainly two kinds of signals were observed at ?68 and ?110 ppm that correspond to T³ and Q⁴ peaks, respectively. This result shows that a fully condensed structure was obtained. The thermal and morphological properties of these coatings materials were investigated by using TGA and SEM techniques. Hardness and abrasion resistance properties of coating materials were examined and both were found to increase with sol–gel precursor content of the coating. The photopolymerization kinetics was investigated by using RT‐IR. 70% conversion was attained with the addition of 15 wt% of BMI resin into the acrylate‐based coating formulation. It was found that the UV‐curable organic–inorganic hybrid coatings improved the surface properties of polycarbonate. Copyright © 2009 John Wiley & Sons, Ltd.     

Rapamycin-cyclodextrin complexation: improved solubility and dissolution rate

The objective of this study was to improve poor aqueous solubility and dissolution properties of anticancer drug rapamycin through formation of inclusion complexes with natural and modified cyclodextrins. Of the cyclodextrins tested, ??-cyclodextrin and hydroxypropyl-??-cyclodextrin did not complex with rapamycin. However, complexes of rapamycin with ??-cyclodextrin, methyl-??-cyclodextrin and hydroxypropyl-??-cyclodextrin were prepared and characterized by techniques such as Fourier Transform infrared spectroscopy, differential scanning calorimetry, phase solubility analysis and in vitro dissolution studies. According to the characterization data for the complexes, rapamycin water solubility was highly enhanced by all three ??-cyclodextrins with methyl-??-cyclodextrin complex resulting in particularly higher solubility enhancement. FTIR spectra and DSC thermograms supported the formation of inclusion complexes. The complexes showed highly improved dissolution rate in water. Complexation with cyclodextrin derivatives such as methyl-??-cyclodextrin and hydroxypropyl-??-cyclodextrin can provide promising alternatives for the formulation of rapamycin.     

Synthesis and properties of a novel redox driven chemiluminescent material built on a terthienyl system

A novel redox driven chemiluminescent material built on a terthienyl system, namely 5,7-di-ethylenedioxythiophen-2-yl-2,3-dihydro-thieno[3,4-d]pyridazine-1,4-dione (ETE-Lum), which is soluble in both organic media and basic aqueous solution was synthesized and characterized. Furthermore, its polymer, PETE-Lum, which is one of the most rare examples of chemiluminescent polymeric materials bearing a pyridazine unit, was obtained successfully by electrochemical means. Both of the materials give chemiluminescence either by treatment with oxidants (H₂O₂ and/or KMnO₄) or by the application of a potential pulse.     

In situ formed silica nanofiber reinforced UV-curable phenylphosphine oxide containing coatings

A series of UV-curable nanocomposite coating materials were prepared by sol–gel technique from tetraethoxysilane (TEOS), methacryloxypropyltrimethoxysilane (MAPTMS) in the presence of urethane acrylate resin based on polyethylene glycol 400 (PEG400). The sol–gel precursor content in the hybrid coatings was varied from 0 to 30 wt.%. In addition, acrylated phenylphosphine oxide oligomer (APPO) is replaced with urethane acrylate resin in order to investigate its effect on the nanocomposite property. The physical and mechanical properties such as; gel content, hardness, adhesion, gloss, impact strength as well as tensile strength were examined. Results from these measurements showed that all the properties of the hybrid coatings improved effectively by gradual increase in sol–gel precursor and APPO resin content. The real time infrared technique was used to follow the degree of acrylic double bond conversion. The thermal stabilities of the UV-cured nanocomposites were investigated by thermogravimetric analysis. The results revealed that the addition of sol–gel precursor and APPO oligomer into the organic network leads to an improvement in the thermal and flame resistance properties of the hybrid materials. It was also determined that the APPO containing hybrid coating with 20 wt.% silica content gave higher char yield than the coating without APPO. It is a desirable achievement to improve simultaneously both the flame retardancy and mechanical properties of a protective coating. SEM studies indicated that inorganic particles were dispersed homogenously through the organic matrix. The hybrids were nanocomposite. It was also found that, incorporation of APPO resin might govern the silica organization and this leading to formation of nanofibrillar structure.     

The effects of surface treatments on the Pt/n-GaAs Schottky interface

The effects of both chemical and laser annealing surface treatment on the electroplated Pt/n-GaAs interface have been studied. Surface studies were carried out using scanning Auger Electron Spectroscopy (SAES) while interface analysis used SAES along with noble ion sputtering. When the Pt/n-GaAs interface is used as a mixer diode, the mixer noise temperature is critically dependent on the chemical nature of that interface, as expressed through the ideality factor, η, and series resistance, R_s. Surface and interface information was obtained in the form of Ga-to-As ratios, (Ga/As), in range of 0.35 to ～2.5. Both chemical treatment and laser annealing showed that excess As at the interface leads to high η values indicating high mixer noise temperatures. Since high η values were accompanied by low barrier heights, φ_B, it was concluded that excess As at the interface lowers the barrier height and decreases the barrier width. This enhanced field emission, an emission mode not acceptable for low mixer noise temperatures. To confine the emission mechanism to thermionic emission requires stoichiometric or Ga rich interfaces and alkaline solutions of H₂O₂ with slow etch rates were found to be best suited for this purpose. Cw laser annealing proved to be a useful technique to control (Ga/As) on GaAs where high vapor pressure of As (uncapped anneal) and high diffusion coefficient of Ga through SiO₂ (capped anneal) were exploited. However, cw annealing was not found to be suitable for mixer diode processing even when Ga rich interfaces are desired, due to sample exposure to oxygen.