Synthesis and characterization of nonaqueous dispersion particles with photolabile α‐heptadecylphenacyl ester stabilizer chains

We describe a new method for the synthesis of core–shell photolabile nanoparticles. The synthesis begins with the batch emulsion copolymerization of n‐butyl methacrylate (BMA) and ethylene glycol dimethacrylate to form small (20‐nm‐diameter) crosslinked particles with a narrow size distribution. These seeds are then used for a second‐stage emulsion copolymerizations in which BMA and various polar monomers, including methacrylic acid, are added under monomer‐starved conditions. After characterization of the particles, they are transferred to an N,N‐dimethylformamide solution. The cesium salt of the carboxylic acid groups is reacted with 2‐bromo‐1‐phenyl‐octadecan‐1‐one to convert various fractions of the ? COOH groups to the corresponding 2‐benzoylheptadecyl ester groups. These aliphatic ester groups render the surface sufficiently hydrophobic that the particles can be dispersed in common aliphatic hydrocarbons solvents to yield colloidal dispersions, sterically stabilized by the dangling aliphatic chains. Ester groups with a phenyl ketone attached to the β‐carbon are photolabile. Irradiation of the particles with UV light detaches the sterically stabilizing chains from the particle and transforms the surface groups back to COOH groups. This leads to flocculation of the particles. The emphasis in this article is on the optimization of the particle synthesis and the characterization of the particles obtained. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2642–2657, 2001     

The formation of dinuclear trichloro-bridged and mononuclear ruthenium complexes from the reactions of dichlorotris(p-tolylphosphine)ruthenium(II) with diazabutadiene ligands

Transition Metal Chemistry - Ru(II) complexes with diazabutadiene (R-DAB) ligands have been prepared. The reaction of RuCl3·nH2O with P(p-tolyl)3 gave a [RuCl2{P(p-tolyl)3}] precursor, whose...     

Synthesis and Crystal Structures of Ethyl 2-(4-Methoxyphenyl)-1<Emphasis Type="Italic">H</Emphasis>-benzo[<Emphasis Type="Italic">d</Emphasis>]imidazole-5-carboxylate Dihydrate and Its Building Block 4-Fluoro-3-nitrobenzoic Acid

The title compound, ethyl 2-(4-methoxyphenyl)-1H-benzo[d]imidazole-5-carboxylate dihydrate (5), was synthesized and its crystal structure was studied by single-crystal X-ray diffraction technique. Compound 5 is crystallized in the centrosymmetric triclinic space group \(P\bar {1}\) with Z?=?4 and Z′?=?2, and unit-cell parameters of a?=?8.9190 (3) Å, b?=?12.6888 (4) Å, c?=?14.7111 (5) Å, α?=?98.4855 (10)°, β?=?101.6379 (9)°, γ?=?95.4346 (10)° and V?=?1599.43 (9) ų. Its starting material, 4-fluoro-3-nitrobenzoic acid (1), is crystallized in the non-centrosymmetric monoclinic space group P2₁ and Z?=?4 with unit-cell parameters of a?=?3.7170 (4) Å, b?=?12.6475 (13) Å, c?=?15.5237 (15) Å, α?=?90°, β?=?91.9786 (16)°, γ?=?90° and V?=?729.35 (13) ų. It was noted that strong hydrogen bonds play important roles in the crystal packing of both compounds, especially in 5, in which the co-crystallized water molecules act as both strong hydrogen bond donor and strong hydrogen bond acceptor.

Graphical Abstract

Two molecule of compound 5 crystallized in a non symmetrical manner with four co-crystallized water molecules which play an important role in the crystal packing as strong hydrogen-bond donors.

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Synthesis and photovoltaic properties of novel C60 bisadducts based on benzo[2,1,3]-thiadiazole

A novel C₆₀ solar cell acceptor (BTOQC, benzo[2,1,3]-thiadiazole-o-quinodimethane-C₆₀ bisadducts) based on benzo[2,1,3]thiadiazole has been synthesized as model to study how the thiadiazole group will affect the device performance in bulk heterojunction organic photovoltaics (BHJ-OPV) with poly(3-hexylthiophene) (P3HT) as donor. The optoelectronic, electrochemistry, and photovoltaic properties of the novel bisadduct BTOQC have been fully investigated. The best device performance of this fullerene derivative in our research was obtained as 2.50% with a high V_oc of 0.74 V.     

A weak‐derivative form for linear hyperbolic systems

Difference schemes for linear hyperbolic systems are considered. As a main result, a weak derivative form (WDF) of the governing equations is derived, which is also valid near flow discontinuities. The occurrence of one‐sided derivatives in the WDF structure indicated how to difference near discontinuities. When first‐order differencing is applied to the WDF result, the (linearly identical) schemes by Godunov, Roe, and Steger‐Warming are reproduced. The extension to nonlinear systems is via a local linearization. Choosing Roe's averaging reduces the WDF algorithm to Roe's scheme, whereas other nonlinear WDF schemes are possible. The suitability of various kinds of averaging is numerically investigated. For weak shocks a surprising lack of sensitivity of the method to a particular averaging is exhibited. However, for strong shocks and where the ordinary arithmetic average is used, a slightly more pronounced difference in performance exists between Roe's scheme and WDF. © 2004 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2004     

En route to a carbohydrate-based vaccine against Burkholderia cepacia

We report a very high yielding first total synthesis of trisaccharide 5, alpha-D-Rhap-(1 --> 3)-alpha-D-Rhap-(1 --> 4)-alpha-D-Galp, corresponding to the repeating unit 1 of an O-polysaccharide present in the lipopolysaccharide of clinical isolate of Burkholderia cepacia. The approach included two successive glycosylations, based on D-rhamnosyl trichloroacetimidate donors 12 and 14. The oligosaccharide 5 has been further functionalized by photochemical coupling or cross-metathesis with non-natural amino acid derivatives. Trisaccharidylamino acids 16 and 17 are now available, with the aim of preparing a novel synthetic carbohydrate-based vaccine.     

Tailoring the charge carrier dynamics in ZnO nanowires: the role of surface hole/electron traps

Post-fabrication thermal-annealed ZnO nanowires (NWs) in an oxidizing (or a reducing) ambient were investigated using transient photoluminescence and X-ray photoelectron spectroscopy. Our findings reveal an ultrafast hole-transfer process to the surface adsorbed oxygen species (e.g., O(2)(-)) occurring within a few hundred picoseconds (ps) in the air-annealed samples; and an ultrafast electron-transfer process to charged oxygen vacancies (i.e., V(O)(2+)) occurring within tens of ps in the H(2)-annealed samples. Contrary to the common perception that the band edge emission (BE) dynamics are strongly influenced by the carrier trapping to the green emission related defect states (i.e., V(Zn)), these above processes compete effectively with the ZnO BE. Hole trapping by ionized V(Zn), which occurs in an ultrashort sub-ps-to-ps timescale (and hence limits its effective hole capture radius), however, has less influence on the BE dynamics. Importantly, our findings shed new light on the photoinduced charge transfer processes that underpins the novel properties of enhanced photocatalytic activity, photovoltaic performance, and photoconductivity response of ZnO NWs, thereby suggesting a strategy for tailoring the ultrafast carrier dynamics in ZnO NW-based devices.     

Time-resolved resonance Raman study of the triplet states of p-hydroxyacetophenone and the p-hydroxyphenacyl diethyl phosphate phototrigger compound

Pico- and nanosecond time-resolved resonance Raman (TR3) spectroscopy have been utilized to study the dynamics and structure of p-hydroxyacetophenone (HA) and the p-hydroxyphenacyl-caged phototrigger compound p-hydroxyphenacyl diethyl phosphate (HPDP) in acetonitrile solution. Transient intermediates were detected and attributed to the triplet states of HA and HPDP. Nanosecond-TR3 measurements were done for two isotopically substituted HA molecules to help better assign the triplet state carbonyl C=O stretching and the ring related vibrational modes. The dynamics of formation and the spectral characteristics for the triplet states were found to be similar for the HA and HPDP. The temporal evolution at very early picosecond time scale indicates there is rapid intersystem crossing (ISC) conversion and subsequent relaxation of the excess energy of the initially produced energetic triplet state. B3LYP/6-311G** density functional theory (DFT) calculations were done to determine the structures and vibrational frequencies for both the triplet and ground states of HA and HPDP. The calculated spectra reproduce the experimental spectra and the observed isotopic shifts reasonably well and were used to make tentative assignments to all the experimentally observed features. The triplet states were found to have extensive conjugated pipi* nature with a single-bond-like carbonyl CO bond. We briefly compare the triplet structure and formation dynamics of HA and HPDP as well as the conformational changes upon going from the ground state to the triplet state. We discuss our present results in relation to the initial pathway for the p-hydroxyphenacyl photodeprotection process. We also compare and discuss the properties of the HA pipi* triplet state relative to the published results of other aromatic carbonyl compounds.