New electroluminescent carbazole-containing conjugated polymer: Synthesis, photophysics, and electroluminescence

Abstract

A new electroluminescent polymer, poly{9-(2-ethylhexyl)carbazole-2,7-diethynylene-alt-tris[2,5-bis(2-ethylhexyloxy)-1,4-phenylenevinylene]} (PCzE-PPV), is synthesized, and its photophysical and electrochemical properties and electroluminescence (EL) are studied. In solution, an intense photoluminescence (PL) emission with a maximum at about 520 nm is observed. PL decay dynamics in solution are best described by a monoexponential function with a lifetime of 0.76 ns. Thin films exhibit an intense PL emission with a slightly red-shifted maximum at 532 nm compared to that in the solution spectra. The polymer oxidizes and reduces quasi-reversibly. The ionization potential (HOMO level) of 5.3 eV and the electron affinity (LUMO level) of 2.80 eV are evaluated from cyclovoltammetric measurements. The electrochemical bandgap value (2.45 eV) is in good agreement with the optical bandgap value. Using new polymer, light-emitting devices (LEDs) with a luminance higher than 3000 cd m−2 and low onset voltages at about 3 V are fabricated. The shape of EL spectra of the LEDs is similar to that of PL spectra of the thin films.