An alternating copolymer consisting of light emitting and electron transporting units

Abstract

An alternating copolymer composed of fluorenedivinylene as the light emitting unit and pyridine as the electron transporting one was synthesized by employing the Wittig reaction. The copolymer which has conjugation throughout the molecular chain is soluble in both polar and nonpolar solvents. The copolymer has a band gap energy of 2.85 eV deduced from an ultraviolet-visible absorption spectrum, and ionization potential and electron affinity of -5.67 and -2.82 eV, respectively, deduced from a cyclic voltammogram. The photoluminescence (PL) emission maximum was observed at 440 or 540 nm depending on the solvent used in making the solution for spin-casting. The copolymer was also capable of transporting electrons and could be used as an electron transporting layer. A light emitting diode (LED) fabricated with a blend of polyvinylcarbazole (PVK) with a fluorene-based light emitting material, and this copolymer as an electron transporting layer, exhibited an electroluminescence (EL) emission maximum at 475 nm with a full width at the half maximum (FWHM) of 50 nm and a quantum efficiency of 0.1%, where indium tin oxide (ITO) and Al were used as the anode and cathode, respectively.