Monday, June 23, 2008
Saturday, June 21, 2008
Synthesis and Properties of Novel Low-Band-Gap Thienopyrazine-Based Poly(heteroarylenevinylene)s
]pyrazine-based poly(heteroarylenevinylene)s (PHAVs) (P-1-P-6) by Horner polycondensation and cyano-PHAVs (P-7-P-9) by Knoevenagel polycondensation have been synthesized in quantitative yields. The copolymers are characterized by NMR, IR, UV, GPC, and elemental analysis. High molecular weight (
w up to 279 000 g/mol), thermostable, soluble, and film-forming materials were obtained. The absorption spectra of the polymers show two peaks located in the UV and visible region from ~384 to 650 nm and are promising for the application in polymer solar cells. The absorption and emission in solution and in solid state of the polymers revealed that the polymers generate a 
-stacked structure in the solid state, and the polymer molecules in the film were ordered. Thin films of the polymers P-1-P-9 exhibit an optical band gap of ~1.56-2.08 eV. Cyclic voltammograms display that the p-doping/dedoping and n-doping/dedoping processes of the polymers (P-1, P-2, P-3, P-5, and P-6) are reversible. The HOMO and LUMO levels of the polymers were determined from electrochemical measurements. From the absorption spectra of the polymers (P-1, P-2, and P-8) in chloroform/methanol mixtures, all the three polymers have revealed solvatochromic effects, which have been related to the formation of aggregates.
Macromolecules, 39 (23 ), 7844 -7853 , 2006
w up to 279 000 g/mol), thermostable, soluble, and film-forming materials were obtained. The absorption spectra of the polymers show two peaks located in the UV and visible region from ~384 to 650 nm and are promising for the application in polymer solar cells. The absorption and emission in solution and in solid state of the polymers revealed that the polymers generate a -stacked structure in the solid state, and the polymer molecules in the film were ordered. Thin films of the polymers P-1-P-9 exhibit an optical band gap of ~1.56-2.08 eV. Cyclic voltammograms display that the p-doping/dedoping and n-doping/dedoping processes of the polymers (P-1, P-2, P-3, P-5, and P-6) are reversible. The HOMO and LUMO levels of the polymers were determined from electrochemical measurements. From the absorption spectra of the polymers (P-1, P-2, and P-8) in chloroform/methanol mixtures, all the three polymers have revealed solvatochromic effects, which have been related to the formation of aggregates.
Star-Shaped Oligofluorenes End-Capped with Carboxylic Groups: Syntheses and Self-Assembly at the Liquid–Solid Interface
A series of star-shaped oligofluorenes end-capped with carboxylic acid groups were synthesized. Different numbers of carboxyl groups that can form hydrogen bonds, and long alkane chains that have stabilizing effects, were intentionally introduced. The resulting molecular architectures of the so-prepared star-shaped oligofluorenes at the liquid–solid interface were investigated by scanning tunneling microscopy. It is found that the number of hydrogen-bonding groups and the symmetry of the target molecules have crucial influences on the structures of the ordered assemblies.
Wednesday, June 18, 2008
Facile Horner-Emmons Synthesis of Defect-Free Poly(9,9-dialkylfluorenyl-2,7-vinylene)
This paper describes a simple new strategy for preparing poly(9,9-dialkylfluorenyl-2,7-vinylenes) (PFVs) having high molecular weights and no detectable saturated defects along the conjugated backbone. The new route utilizes a modified Horner-Emmons method by coupling suitably designed comonomers to form the targeted conjugated polymers. The newly prepared PFVs were directly compared to PFVs prepared via a previously established Gilch polymerization route. The structure and optical properties of all PFVs were characterized by gel permeation chromatography (GPC), NMR spectroscopy, UV-vis, fluorescence, and photoluminescence spectroscopy. The findings indicate that the modified Horner-Emmons route gave PFVs with lower molecular weights but substantially higher yields and fewer defects than those prepared by using the Gilch route.
Macromolecules, 39 (10 ), 3494 -3499 , 2006 .
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