Browsing by Subject "Aqueous medium"

Now showing 1 - 2 of 2

Open Access
The effect of cucurbit[n]uril on the solubility, morphology, and the photophysical properties of nonionic conjugated polymers in an aqueous medium
(2010) Tuncel, D.; Artar, M.; Hanay, S. B.
The effects of cucurbit[n]uril on the dissolution and the photophysical properties of nonionic conjugated polymers in water are described. For this purpose, a fluorine-based polymer, namely, poly[9,9-bis{6(N,N-dimethylamino) hexyl}fluorene-co-2,5-thienylene (PFT) was synthesized and characterized by spectroscopic techniques including 1D and 2D NMR, UV-vis, fluorescent spectroscopy, and matrix-assisted laser desorption mass spectrometry (MALDI-MS). For the first time, it was demonstrated that a nonionic conjugated polymer can be made soluble in water through an inclusion complex formation with CB8. The structure of the complex was elucidated by NMR experiments including 1H and selective 1D-NOESY. This complex emits green and is highly fluorescent with fluorescent quantum yield of 35%. In contrast, CB6 or water-soluble CB7 although they are chemically identical to CB8 do not have any effect on the dissolution and photophysical properties of PFT. By preparing a protonated version of PFT, the optical properties of PFT in methanol, protonated PFT and PFT@CB8 in water have been studied and compared. It was also observed that the morphology of the polymer PFT was affected by the presence of CB8. Thus CB8-assisted self-assembly of polymer chains leads to vesicles formation; these structures were characterized by DLS, AFM, SEM, and TEM fluorescent optical microscopy.
Open Access
Optical response of Ag-Au bimetallic nanoparticles to electron storage in aqueous medium
(2008) Tunc, I.; Guvenc, H. O.; Sezen, H.; Süzer, Şefik; Correa-Duarte, M. A.; Liz-Marzán, L. M.
Composition and structure dependence of the shift in the position of the surface plasmon resonance band upon introduction of NaBH 4 to aqueous solutions of gold and silver nanoparticles are presented. Silver and gold nanoalloys in different compositions were prepared by co-reduction of the corresponding salt mixtures using sodium citrate as the reducing agent. After addition of NaBH 4 to the resultant nanoalloys, the maximum of their surface plasmon resonance band, ranging between that of pure silver (ca. 400 nm) and of pure gold (ca. 530 nm), is blue-shifted as a result of electron storage on the particles. The extent of this blue shift increases non-linearly with the mole fraction of silver in the nanoparticle, parallel to the trends reported previously for both the frequency and the extinction coefficient of the plasmon band shifts. Gold(core)@silver(shell) nanoparticles were prepared by sequential reduction of gold and silver, where addition of NaBH 4 results in relatively large spectral shift in the plasmon resonance band when compared with the nanoalloys having a similar overall composition. The origin of the large plasmon band shift in the core-shell is related with a higher silver surface concentration on these particles. Hence, the chemical nature of the nanoparticle emerges as the dominating factor contributing to the extent of the spectral shift as a result of electron storage in bimetallic systems. Copyright © 2008 American Scientific Publishers All rights reserved.