We report the preparation of nanoscaled PS/PMMA core-shell spheres with highly fluorescent CdS/ZnS coated CdSe quantum dots (QDs) integrated in the core. Core-shell spheres of different diameters have been self-assembled to colloidal photonic crystals (PCs) with photonic stop bands located in the visible range of the electromagnetic spectrum. For the synthesis of the core, a modified miniemulsion polymerization has been used; the shell was prepared by a newly developed core-shell polymerization. The CdSe QDs embedded in the core were coated with the higher band gap semiconductor materials CdS and ZnS in a successive ion layer adsorption reaction (SILAR) keeping up the light-emitting properties of the QDs during the integration process. A modifying influence of the photonic band structure of the PC on the photoluminescence (PL) of the embedded QDs was observed by angular-dependent fluorescence measurements. The controlled combination of electronic confinement, originating from the QDs, and photon confinement, due to the periodic dielectric structure of the colloidal crystal, as it has been realized in this work presents a huge platform for the design and construction of novel optoelectronic devices based on PCs.
We report a bottom-up synthesis of a photochemically and thermally active azobenzene-based polyelectrolyte multilayer (PEM) planar defect embedded in a colloidal photonic crystal (CPC). Both photoisomerization and thermal cycling lead to a precise tuning of an intragap transmitting state induced by the PEM structural defect.
the second harmonic (527 nm) of a Nd:YLF laser operating at 100 MHz. The dye laser contained a single plate birefringent filter tuned to produce laser oscillation at 610 nm and a pulse width of approximately 1 ps full width at half maximum (FWHM). The dye laser was cavity-dumped at 1 MHz, and then frequency doubled using a potassium dihydrogen phosphate nonlinear crystal. Sample fluorescence was spectrally filtered with a monochromator (bandpass ∼ 10 nm) and detected with a cooled microchannel plate (PMT, Hamamatsu R2809U-11). Fluorescence transients were measured at the magic angle, 54.7° [24]. Temporal response function of the system was measured to a FWHM of ca. 50 ps.Construction of QD-Protein Conjugate Model: A model for the three-dimensional conformation of Cy3-maleimide was constructed using Chem-3D Ultra 8.0 (CambridgeSoft, Cambridge, MA). Using energy minimization MM2, low-energy conformers were located using the MM2 molecular dynamics module within Chem-3D Ultra. Conformer energies ranged from 17.9 to 23.0 kcal mol -1 . A low-energy conformer was selected, which had the maleimide oriented such that it could interact with a cysteine side chain on the protein to form a covalent bond. The Cy3-maleimide model was merged with the X-ray crystal structure of MBP using MidasPlus [16,25]. The preferred orientation of QD-surface-located MBP was previously investigated [16]. An optimal configuration of the QD-MBP-His assembly is assumed in the present analysis. Fitting of the open and closed forms of MBP was performed within MidasPlus by aligning six a carbons of residues in one of the two MBP lobes in the structure. Distance between the Cy3 fluorophore and the QD center was 73.7 Å corresponding to the previously ascertained value [16]. Photonic crystals (PCs) are characterized by a spatially periodic dielectric constant modulation, and can suppress, slow, or guide the flow of electromagnetic radiation in certain lattice directions when the periodicity is comparable to the radiation wavelength. [1,2] These attributes have made them promising candidates for a variety of optoelectronic devices COMMUNICATIONS
The Arrhenius parameters of the propagation rate coefficient, k p, are determined via the IUPAC recommended pulsed laser polymerization–size exclusion chromatography (PLP-SEC) method for two linear alkyl acrylates (stearyl and behenyl acrylate), four branched alkyl acrylates (isononyl (INA-A), tridecyl (TDN-A and TDA-A), and henicosyl acrylate (C21A)), and two branched alkyl methacrylates (tridecyl methacrylates (TDN-MA and TDA-MA)) in bulk. Furthermore, the above stated acrylates and heptadecyl acrylate (C17A) were studied in 1 M solution in butyl acetate (BuAc). On the basis of such a wide data basis in combination with the already literature known data of relatives of the herein investigated monomers, we are able to identify and extend global trends and family type behavior for the propagation rate coefficients of a wide array of alkyl (meth)acrylates. In order to ensure a valid SEC evaluation, the polymer specific Mark–Houwnik–Kuhn–Sakurada (MHKS) parameters are determined for each of the polymers, via multidetector SEC analysis (multi angle laser light scattering (MALLS) in combination with differential viscosimetry (Visco) and refractive index (RI)) of narrowly distributed polymer samples obtained via fraction with a preparative SEC column. By employing further physicochemical polymer specific data (e.g., glass transition temperatures (T g)), we provide a hypothesis for the reported trends and family type behaviors: (i) the steady increase of k p with increasing ester side chain length for linear alkyl (meth)acrylates may be explained by a decreasing concentration of the polar ester moieties, resulting in a decreasing stabilization of the attacking radical in the transition state of the propagation reaction, and (ii) the family type behavior of the branched alkyl methacrylates can be understood by considering steric and entropic influences. For the branched alkyl acrylates, no clear trend is detectable, and a family type behavior is clearly not observed in contrast to the corresponding methacrylates.
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