Conjugated Polymer Nanoparticle‐Triplet Emitter Hybrids in Aqueous Dispersion: Fabrication and Fluorescence Quenching Behavior

Conjugated polymer nanoparticles based on poly[9,9‐bis(2‐ethylhexyl)fluorene] and poly[N‐(2,4,6‐trimethylphenyl)‐N,N‐diphenylamine)‐4,4′‐diyl] are fabricated using anionic surfactant sodium dodecylsulphate in water by miniemulsion technique. Average diameters of polyfluorene and polytriarylamine nanoparticles range from 70 to 100 and 100 to 140 nm, respectively. The surface of the nanoparticles is decorated with triplet emitting dye, tris(2,2′‐bipyridyl)ruthenium(II) chloride. Intriguing photophysics of aqueous dispersions of these hybrid nanoparticles is investigated. Nearly 50% quenching of fluorescence is observed in the case of dye‐coated polyfluorene nanoparticles; excitation energy transfer is found to be the dominant quenching mechanism. On the other hand, nearly complete quenching of emission is noticed in polytriarylamine nanoparticle‐dye hybrids. It is proposed that the excited state electron transfer from the electron‐rich polytriarylamine donor polymer to Ru complex leads to the complete quenching of emission of polytriarylamine nanoparticles. The current study offers promising avenues for developing aqueous solution processed‐electroluminescent devices involving a conjugated polymer nanoparticle host and Ru or Ir‐based triplet emitting dye as the guest.

     

Molecular-glue-triggered DNA assembly to form a robust and photoresponsive nano-network

A robust and photoresponsive DNA network has been designed and constructed from branched DNA and molecular glue. The molecular glue is photoswitchable and can specifically bind to G-G mismatched double-stranded DNA. The assembly process can be reversibly controlled by manipulating the wavelength of light. The approach is flexible, allowing tuning of the size, morphology as well as the cavity of the network by variation of the molar ratio and the isotropic/anisotropic character of the branched building blocks. The assembled architectures are versatile and heat tolerant. These properties should allow the use of the network in further applications.     

Single microdroplet/water extraction and in situ microanalysis by microcapillary injection and differential pulse voltammetry.

A redox species was extracted from water (50 x 10(-6) dm3) into a single micro-oil-droplet (30 x 10(-12) dm3) in contact with a microelectrode using microcapillary injection and manipulation techniques. Further, an in situ microanalysis of the solute in a single oil droplet was demonstrated by differential pulse voltammetry. The redox species of 10(-16) mol concentrated in the droplet could be quantitatively analyzed independently of the distribution coefficient of the solute between the oil and water phases. The potential of this technique was considered in terms of the preconcentration and separation as well as a microanalysis and an ultratrace analysis.     

Photoisomerizable bipyridine ligands and macroligands: absorption, photoisomerization properties and theoretical study.

Two 2,2'-bipyridines, substituted at the 4,4'-positions by p-dialkylaminophenylazostyryl moieties p-R2N-C6H4-N=N-C6H4-CH=CH-[6 a, R2N=nBu2N; 6 b, R2N=(nBu)(C4H8OTHP)N; 6 c, R2N=(nBu)(C4H8OH)N], were successfully synthesized by using Wadworth-Emmons reactions. The X-ray structure of 6 a has been determined. Esterification of 6 c with 2-bromoisobutyroylbromide afforded 6 d. This ligand was used as an initiator for the living radical polymerization of methylmethacrylate (MMA) and gave rise to macroligand 6 e. Thin films of good optical quality were obtained by the spin-coating technique. Photoisomerization experiments were carried out on 6 a in solution and on 6 e in both solution and film, and the kinetics of photochemical (E/Z) and thermal (Z/E) isomerization were investigated. They were found to show Z-E back isomerization typical of aminoazobenzene-type rather than of push-pull-type molecules. Density functional theoretical (TD-DFT) calculations were performed on model compound 6 a' (R2N=Me2N) to understand the structural and electronic transitions of the corresponding E-E, E-Z and Z-Z isomers. It was found that the E-E isomer is almost planar as observed experimentally by X-ray diffraction, whereas the Z-Z isomer, which is 35.4 kcal mol(-1) less stable than the E-E isomer, is nonplanar. The theoretical studies also reveal that several transitions of pi-pi*, n-pi* and charge-transfer (CT) types, are involved in the long-wavelength transition of 6 a (E-E). The same observations can be made for the (Z-Z) isomer, and the TD-DFT simulated spectrum fits quite nicely to the experimental, reproducing and explaining the apparition of a blue-shifted charge-transfer band at 390 nm.     

Reinforcing effect of bi- and tri-cyclopolyprenols on ‘primitive’ membranes made of polyprenyl phosphates

Cholesterol plays the role of membrane reinforcer in eukaryotes, whereas hopanoids play the same role in bacteria. Which components could have reinforced ‘primitive’ membranes? We describe here an efficient biomimetic synthesis of bi- and tri-cyclopolyprenols and demonstrate that these compounds reinforce the membranes of polyprenyl phosphate, which we speculated as ‘primitive’ membranes.     

Novel synthesis of brefeldin a an application of the oxidative fragmentation of γ-hydroxyalkyl stannanes

Synthesis of Brefeldin A seco acid (13) involving new oxidative fragmentation was reported.     

Synthesis of c27-substituted ecdysteroids,potential tools for biochemical studies

A sequence of selective protection procedures is described, facilitating the efficient cleavage of the ecdysteroid side-chain, which can then be reconstructed; in this way, C-27 ether-linked analogues of ecdysteroids have been synthesized, one of which displays highly significant biological activities.     

Dendritic effects on the ordered assembly and the interfacial one-electron oxidation of redox-active dendron-functionalized gold nanoparticles

A higher generation dendron with a long-alkyl chain thiol (DA2-SH) induced the formation of nanoparticles with a small core with quite a narrow size distribution (1.5 +/- 0.1 nm), the self-assembly of one-dimensional arrays of these gold nanoparticles (DA2-Au), and the stabilization for the formation of the radical cation of the phenothiazine of DA2-Au nanoparticles from the interfacial one-electron oxidation of the nanoparticles with NOBF4.