Synthesis and characterization of a novel blue electroluminescent polymer constituted of alternating carbazole and aromatic oxadiazole units

Abstract

A novel copolymer poly[N-(2′-ethylhexyl)-carbazole-3,6-diyl-1″,3″,4″-oxadiazole-2″,5″-diyl-2‴,5‴-dioctyloxy-1‴,4‴-phenylene-1,3,4-oxadiazole-2,5-diyl] (PCOPO) containing an electron rich carbazole moiety and an electron deficient aromatic oxadiazole unit is synthesized by a polycondensation reaction. The structure of the polymer is confirmed by FT-IR, NMR, and elemental analysis. PCOPO can be partially dissolved in THF, CHCl3, xylene, and DMSO while it can be completely dissolved in chloroform with a small amount of trifluoroacetic acid (TFA). The optical and electronic properties of the polymer are investigated by UV-Vis absorption and photoluminescence spectroscopy as well as cyclic voltammetry. The results show that the polymer films emit greenish-blue light (475 nm). The bandgap energy of the polymer is estimated by the optical method (2.82 eV) and the electrochemical measurement (2.94 eV), respectively. Both p-doping and n-doping processes are observed in cyclic voltammetric investigation. The HOMO and LUMO energies of the polymer are estimated to be 5.60 and 2.66 eV, respectively. The photophysical and electronic properties as well as the preliminary electroluminescent device result of the polymer demonstrate that it may be a promising candidate material for the fabrication of an efficient polymer light-emitting device.