Poly Degree Of Polymerization Of Phenylacetylene Derivatives And Luminescent Properties Of Relations

Poly(p-phenylenevinylene)(PPV) and its derivatives have been widely studied since the materials are discovered in 1990. Due to physical properties such as conductivity, photoluminescence and electroluminescence, PPV and its derivatives are extensively applied in organic light-emitting diodes. Because of insolubility of PPV, much previous research work has been done to improve the solubility by attaching side groups at the positions2, 5 of the phenylene rings such as alkyl, phenyl and alkoxy or change the solubility properties by modifying the main chains of PPV and its derivatives. A variety of substituents attached to the backbone of poly (p-phenylenevinylene) have presented different material physical properties. In theory, there exists the relationship between molecular weight and its fluorescence properties. Our research work would focus on the relationship between molecular weight and the fluorescence emission wavelength.The monomers are prepared by Williamson synthetic method and Blanc Chloromethylation Reaction, respectively. A few approaches have been reported to synthesize the soluble dialkoxy PPVs, however, the most generally used methods for synthesis of the PPVs are Gilch and Wessling routes. we will adopt the Gilch route in the paper.The chemical structures of monomers and polymers are characterized by FTIR and Nuclear magnetic resonance (NMR) spectra. Molecular weights of the polymers are measured in THF by gel permeation chromatography (GPC). Fluorescence emission spectra of the polymers are obtained by Molecular fluorospectrometry.Polymers with different molecular weight are obtained by extracting using the methanol and ether as the extraction solvents and the silica column chromatography method, respectively.The research on the relationship between molecular weight and the fluorescence emission wavelength shows that the emission wavelength shifts from 543 to 621 nm while increasing the molecular weight from 7765 to 38751. However,the fluorescence spectra present blue shift as the molecular weight increases to 354931. The emission spectra can be assumed to result from the intramolecular charge transfer when the interchain interactions can be neglected. The effective conjugation length will increase at low molecular weight while the molecular weight increases. However, the effective conjugation length will decrease at high molecular weight while the molecular weight increases. The effective conjugation length can be limited by a variety of factors such as chemical or structural defects. Although some modified synthesis processes are adopted, realistic PPVs can also contain different types of defects. Among these defects, tolane-bisbenzyl (TBB) is the most possible defect which shows that the triple and single bonds may replace the double bonds. From the Comparison of the 1H NMR spectra of polymers with different molecular weight , the contents of the single and triple bonds for the polymer with the molecular weight of 354931 are about 3% and 6%,while the amount of the single bonds for polymer with the molecular weight of 38751 can be estimated to be 2%.