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Journal of Polymer Science Part B: Polymer Physics, 2006
Angewandte Chemie International Edition in English, 1988
The nonaromatic primary product 2 is apparently so unstable that it spontaneously rearranges to g... more The nonaromatic primary product 2 is apparently so unstable that it spontaneously rearranges to give the thermodynamically favored alkylpolyphosphanes. No evidence for dimers of 2 was found. L Lip5 + LiC Me + FeCI2-2 THF Licl P I[~5-P51Fel~5-C5Megll 5 5
Journal of the American Chemical Society, 2004
Dimensionality is known to play a key role in the solution behavior of nano-and mesoparticles. In... more Dimensionality is known to play a key role in the solution behavior of nano-and mesoparticles. In particular, the shape and the range of the attractive van der Waals interparticle potential are determined by the number of microscopic versus mesoscopic dimensions. For single-walled nanotubes (SWNTs), where two of the dimensions are nanoscopic and one is mesoscopic, the intertube attraction is relatively short ranged, albeit very steep. The very large attraction (compared to the thermal energy, KbT) among long SWNTs leads to aggregation at different levels and constitutes a major barrier for manipulation and utilization of SWNTs. This study demonstrates that it is possible to shape the intertube potential by decorating SWNTs with end-tethered polymers. In good solvent conditions for the polymers, entropic repulsion among the tethered chains generates a free energy barrier that prevents SWNTs from approaching the attractive part of the intertube potential. Consequentially, stable dispersions of individual, well separated SWNTs can be prepared. Investigation of different chain lengths and tethering densities of the polymers as well as the interparticle potentials for nanometric versus mesoscopic particles suggests that polymer-induced steric stabilization provides a generic method for separation of SWNTs from mixtures of colloidal species, as demonstrated experimentally.
![Research paper thumbnail of Poly[(2-alkoxy-5-methyl-1,3-phenylene vinylene)-alt-(phenylene vinylene)] derivatives with different contents ofcis- andtrans-olefins: The effect of the olefin bond geometry and conjugation length on luminescence](https://a.academia-assets.com/images/blank-paper.jpg)
](Journal of Polymer Science Part A: Polymer Chemistry, 2003
Poly[(2-alkyloxy-5-methyl-1,3-phenylenevinylene)-alt-(1,3-phenylenevinylene)]s (8) and poly[(2-al... more Poly[(2-alkyloxy-5-methyl-1,3-phenylenevinylene)-alt-(1,3-phenylenevinylene)]s (8) and poly[(2-alkyloxy-5-methyl-1,3-phenylenevinylene)-alt-(1,4-phenylenevinylene)]s (10) were synthesized by the Wittig reaction to provide materials containing 45–62% cis-vinylene bonds. The optical characteristics of 8 and 10 were compared with those of their respective isomers, 3 and 4, the cis-vinylene contents of which were significantly lower (9–16%). Although a greater fraction of cis-CHCH linkages caused the absorption maximum (λmax) of 8 and 10 to be slightly blueshifted (by ∼3–6 nm) from that of 3 and 4, the impact of the vinylene bond geometry appeared to be negligible on their fluorescence spectra. The fluorescence quantum efficiencies of 8 and 10 were estimated to be approximately 0.25 and 0.72, respectively. Both 8 (λmax ≈ 445 or 462 nm) and 10 (λmax ≈ 480 or 506 nm) were electroluminescent, showing effective color tuning by the controlled insertion of m-phenylene moieties. The external electroluminescence quantum efficiencies were determined to be 4.26 × 10−3% for 8 and 0.63% for 10. The cis/trans-vinylene bond ratio had a great impact on the electroluminescence device performance of 8 but a much smaller impact on the performance of 10. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 303–316, 2004
Journal of Polymer Science Part B: Polymer Physics, 2006
Angewandte Chemie International Edition in English, 1988
The nonaromatic primary product 2 is apparently so unstable that it spontaneously rearranges to g... more The nonaromatic primary product 2 is apparently so unstable that it spontaneously rearranges to give the thermodynamically favored alkylpolyphosphanes. No evidence for dimers of 2 was found. L Lip5 + LiC Me + FeCI2-2 THF Licl P I[~5-P51Fel~5-C5Megll 5 5
Journal of the American Chemical Society, 2004
Dimensionality is known to play a key role in the solution behavior of nano-and mesoparticles. In... more Dimensionality is known to play a key role in the solution behavior of nano-and mesoparticles. In particular, the shape and the range of the attractive van der Waals interparticle potential are determined by the number of microscopic versus mesoscopic dimensions. For single-walled nanotubes (SWNTs), where two of the dimensions are nanoscopic and one is mesoscopic, the intertube attraction is relatively short ranged, albeit very steep. The very large attraction (compared to the thermal energy, KbT) among long SWNTs leads to aggregation at different levels and constitutes a major barrier for manipulation and utilization of SWNTs. This study demonstrates that it is possible to shape the intertube potential by decorating SWNTs with end-tethered polymers. In good solvent conditions for the polymers, entropic repulsion among the tethered chains generates a free energy barrier that prevents SWNTs from approaching the attractive part of the intertube potential. Consequentially, stable dispersions of individual, well separated SWNTs can be prepared. Investigation of different chain lengths and tethering densities of the polymers as well as the interparticle potentials for nanometric versus mesoscopic particles suggests that polymer-induced steric stabilization provides a generic method for separation of SWNTs from mixtures of colloidal species, as demonstrated experimentally.
Journal of Polymer Science Part A: Polymer Chemistry, 2003
Poly[(2-alkyloxy-5-methyl-1,3-phenylenevinylene)-alt-(1,3-phenylenevinylene)]s (8) and poly[(2-al... more Poly[(2-alkyloxy-5-methyl-1,3-phenylenevinylene)-alt-(1,3-phenylenevinylene)]s (8) and poly[(2-alkyloxy-5-methyl-1,3-phenylenevinylene)-alt-(1,4-phenylenevinylene)]s (10) were synthesized by the Wittig reaction to provide materials containing 45–62% cis-vinylene bonds. The optical characteristics of 8 and 10 were compared with those of their respective isomers, 3 and 4, the cis-vinylene contents of which were significantly lower (9–16%). Although a greater fraction of cis-CHCH linkages caused the absorption maximum (λmax) of 8 and 10 to be slightly blueshifted (by ∼3–6 nm) from that of 3 and 4, the impact of the vinylene bond geometry appeared to be negligible on their fluorescence spectra. The fluorescence quantum efficiencies of 8 and 10 were estimated to be approximately 0.25 and 0.72, respectively. Both 8 (λmax ≈ 445 or 462 nm) and 10 (λmax ≈ 480 or 506 nm) were electroluminescent, showing effective color tuning by the controlled insertion of m-phenylene moieties. The external electroluminescence quantum efficiencies were determined to be 4.26 × 10−3% for 8 and 0.63% for 10. The cis/trans-vinylene bond ratio had a great impact on the electroluminescence device performance of 8 but a much smaller impact on the performance of 10. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 303–316, 2004