Synthesis and Characterization of Low Content of Structural Defects of Aryl-Substituted Electroluminescent Poly( p -phen
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Synthesis and Characterization of Low Content of Structural Defects of Aryl-Substituted Electroluminescent Poly(p-phenylenevinylene)s Zhi-Kuan Chen, Nancy Hoi Sim Lee, and Wei Huang Institute of Materials Research and Engineering (IMRE), Singapore 117602 ABSTRACT We report the synthesis and characterization of a novel series of aryl-substituted PPVs, which have shown excellent processability, good thermal stability, high photoluminescence quantum efficiency and low content of structural defects. The substituents of the polymers were designed with different degree of hindrance effect on the main chain. 1H NMR measurement indicates that the defect structure in the polymer main chain can be effectively depressed by introducing bulk and hindrance substituents. INTRODUCTION Electroluminescent conjugated polymers based on poly(p-phenylene vinylene) (PPV) have been a subject of interest due to their potential applications in polymer light-emitting devices (PLEDs) [1,2]. Among others, soluble phenyl-substituted PPVs (Ph-PPVs) have shown the most promising features, such as high luminance efficiencies and power efficiencies, and relatively low driving voltages for PLED applications [3-5]. However, Ph-PPVs, prepared through the Gilch route, have demonstrated large amount of structural defects in the polymer main chains, which was believed to be one of the key factors limiting the device lifetime [6]. Herein, we report the synthesis and characterization of a series of dialkoxy phenyl-substituted PPV derivatives. The polymers possess dialkoxy long chains and phenyl ring in the side chain in order to render improved solubility in common organic solvents, as well as to minimize interchain interactions and thus achieve high photoluminescence quantum efficiencies. In addition, introduction of such bulk substituents into the polymer is aiming at depression of the structural defects in the polymer backbone, which was formed during the polymerization process by the Gilch method. The chemical structures of the polymers are shown in Figure 1.
OEH
OEH OEH
EHO
EHO
n
n O-PPV
OEH
M-PPV
Figure 1. The chemical structures of the polymers
C8.29.1
n P-PPV
EXPERIMENTAL DETAILS Nuclear magnetic resonance (NMR) spectra were collected on a Bruker ACF 300 spectrometer using chloroform-d as a solvent and tetramethylsilane (TMS) as an internal standard. Electron impact mass spectra were obtained from a Micromass VG7035F mass spectrometer using an ion current of 70 eV. Fourier transform infrared (FT-IR) spectra were recorded on a Bio-Rad FTS 165 spectrometer by dispersing samples in KBr discs. Ultravioletvisible (UV-vis) and fluorescence spectra were obtained using a Shimadzu UV 3101PC UV-visNIR spectrophotometer and a Perkin Elmer LS 50B luminescence spectrometer with a xenon lamp as light source respectively. Elemental analyses were performed on a Perkin Elmer 2400 elemental analyzer for C, H and Br determination. Thermogravimetric analyses (TGA) were conducted on a Du Pont Thermal Analyst 2100 system with a TGA 2950 thermogravimetric ana
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