The photo-and-thiol-driven trans insertion of phenylacetylene into H-Pt bonds of Pt(X)(H)(PPh3)2 (X = SAr, Cl, Br, and I) took place to afford Pt[(Z)-C(H)=CH(Ph)](X)(PPh3)2 in good yields. 相似文献
Nitroxide‐mediated polymerizations of styrene in microemulsion have been carried out at 125 °C using the cationic surfactant tetradecyltrimethylammonium bromide and the nitroxides 2,2,6,6‐tetramethylpiperidinyl‐1‐oxy (TEMPO) and N‐tert‐butyl‐N‐[1‐diethylphosphono‐(2,2‐dimethylpropyl)] nitroxide (SG1). TEMPO‐mediated polymerizations were extremely slow, with large particles (dn = 39–129 nm) and broad molecular weight distributions (MWDs). The origin of the broad MWDs was likely significant alkoxyamine decomposition and differing diffusion rates of monomer and low MW alkoxyamines (and nitroxide) between monomer‐swollen micelles and polymer particles. SG1‐mediated polymerizations proceeded at higher rates, resulting in nanoparticles (dn = 21–37 nm) and lower than for TEMPO.
Circularly polarized luminescence (CPL) was observed in pyrene zipper arrays helically arranged on an RNA duplex. Hybridization of complementary RNA strands having multiple (two to five) 2′‐O‐pyrenylmethyl modified nucleosides affords an RNA duplex with normal thermal stability. The pyrene fluorophores are assembled like a zipper in a well‐defined helical manner along the axis of RNA duplex, which, upon 350 nm UV illumination, resulted in CPL emission with pyrene excimer formation. CPL (glum) levels observed for the pyrene arrays in dilute aqueous solution were +2×10?2–+3.5×10?2, which are comparable with |glum| for chiral organic molecules and related systems. The positive CPL signals are consistent with a right‐handed helical structure. Temperature dependence on CPL emission indicates that the stable rigid RNA structure is responsible for the strong CPL signals. The single pyrene‐modified RNA duplex did not show any CPL signal. 相似文献
A novel yellow fluorescent diisocyanate 3,6-di(hexamethylene urethano)spiro[xanthene-9,3′-phthalide] diisocyanate (DIX) was synthesized by the reaction of fluorescein with hexamethylene diisocyanate first. Using DIX to substitute partially isophorone diisocyanate (IPDI), a kind of yellow fluorescent waterborne polyurethane DIX-WPU was prepared by blocking the fluorophore of DIX into the polyurethane chain using IPDI, polytetramethylene ether glycol and 2,2-dimethylol propionic acid. The molecular structure of DIX and DIX-WPU was confirmed by means of Fourier transform infrared spectroscopy. The fluorophore is fixed permanently in the polyurethane chain and is difficult to migrate due to the covalent bonding with other component during the synthesis. The fluorescence intensity of DIX-WPU fluorescent dispersion was enhanced greatly comparing with that of fluorescein in a wide range of fluorophore content between 1 × 10–7 and 1 × 10–3 mol/L. The fluorescence of DIX-WPU dispersion is very stable not only for the long term storage but also for the fluorescence quencher. It was found that the fluorescence intensity of DIX-WPU increased with the increase of temperature. 相似文献
This work demonstrates a selection criteria that determines whether molecular assembly occurs through a one‐step or stepwise manner in ligand‐bridged dinuclear zinc(II) (Zn2+) complex formation, which is associated with the π stacking of building blocks. The building blocks of carbazole ligands ( L1 and L4 ) that contain two imidazole moieties at the 3,6‐positions form 4:2 complexes (i.e., [ L ]4?(Zn2+)2) at a molar ratio of 0.50 ([Zn2+]/[ L ]0=0.50), thereby providing π stacking between the carbazole ligands. At the molar ratio of 0.67 ([Zn2+]/[ L ]0=0.67), the 4:2 complexes change to 3:2 complexes (i.e., [ L ]3?(Zn2+)2) with no π‐stacked carbazole unit. In contrast, when the imidazole groups in L1 are replaced with benzoimidazole groups ( L3 ), L3 also yields the 4:2 complex [( L3 )4?(Zn2+)2] at a molar ratio of 0.50. However, there is no structural transition from ( L3 )4?(Zn2+)2 to other complex species above a molar ratio of 0.50. Similarly, when two imidazole groups are introduced into the carbazole ring at 2,7‐positions ( L5 ), L5 also gives the 4:2 complex [( L5 )4?(Zn2+)2] that shows no structural transition to other complex species at a higher molar ratio. 相似文献
Directing the supramolecular polymerization towards a preferred type of organization is extremely important in the design of functional soft materials. Proposed herein is a simple methodology to tune the length and optical chirality of supramolecular polymers formed from a chiral bichromophoric binaphthalene by the control of enantiomeric excess (ee). The enantiopure compound gave thin fibers longer than a few microns, while the racemic mixture favored the formation of nanoparticles. The thermodynamic study unveils that the heterochiral assembly gets preference over the homochiral assembly. The stronger heterochiral binding over homochiral one terminated the elongation of fibrous assembly, thus leading to a control over the length of fibers in the nonracemic mixtures. The supramolecular polymerization driven by π–π interactions highlights the effect of the geometry of a twisted π‐core on this self‐sorting assembly. 相似文献