Synthesis and characterization of novel soluble alternating copoly(phenylene vinylene) derivative for light-emitting electrochemical cell

A novel alternating copolymer, poly([2,5-di(2-(2-ethoxy ethoxy)ethoxy)-1,4-phenylene vinylene]-alt1,4-[phenylene vinylene)], has been synthesized through the Wittig condensation as electroluminescent material. In this copolymer, one component is phenylene vinylene with flexible oligo(ethylene oxide) side chain that facilitates ion transportation and phase miscibility between nonpolar and polar part of composite luminescent layer, and another is a rigid phenylene vinylene moiety to improve luminescent quantum efficiency and tune color. The copolymer shows good solubility and thermal stability for device fabrication compared to poly(phpeylene vinylene)(PPV). The band gap value of copolymer is between those of corresponding homopolymers, which indicates that alternating copolymerization is a suitable way to obtain luminescent polymer with desired band gap. The maximum wavelength of photoluminescence of copolymer is 539 nm (yellowish-green). The HOMO and LUMO energy levels obtained by cyclic voltammetry measurement indicate that the electron injection ability of copolymer has been greatly improved compared with that of the PPV. A more balanced carrier injection and higher quantum efficiency are proved by electroluminescent properties of corresponding light-emitting devices. The turn-on voltage of LEC device (ITO/copolymer + PEO + Li-CIO4/Al) is found to be 2.3 V, with current comparative to LED (ITO/ copolymer /Al) at 9.5 V. (C) 2003 Wiley Periodicals, Inc.