Novel Poly(p-phenylenevinylene)s Derivatives with CF3-Phenyl Substituent for Light-Emitting Diodes

Abstract

New PPV derivatives which contain electron-withdrawing trifluoromethyl (CF 3 ) group, poly[2-(2-ethylhexyl-oxy)-5-(4-trifluoro methylphenyl)-1,4-phenylenevinylene] (EHCF 3 P-PPV), and poly[2-(2-ethylhexyloxy)-5-(3,5-bis(trifluoromethyl)-phenyl)-l,4-phenylenevinylene] (EHBCF 3 P-PPV), have been synthesized by GILCH polymerization. As the result of the introduction of the electron-withdrawing CF 3 group to the phenyl substituent, the LUMO and HOMO energy levels of EHCF 3 P-PPV (2.8, 5.1 eV) and EHBCF 3 P-PPV (3.0, 5.3 eV) were lower than those of known poly[2-(2-ethylhexyloxy)-5-phenyl-1,4-phenylenevinylene] (EHP-PPV) (2.6, 4.9 eV). These polymers have been used as the electroluminescent (EL) layers in double layer light-emitting diodes (LEDs) (ITO/PEDOT/polymer/Al). EHCF 3 P-PPV, and EHBCF 3 P-PPV show maximum photoluminescence (PL) peaks at λ m a x = 550, 539 nm, and maximum EL peak at λ m a x = 545, 540 nm, respectively. The current-voltage-luminance (I-V-L) characteristics of the polymers show that turn-on voltages of EHCF 3 P-PPV and EHBCF 3 P-PPV are around 4.0 and 3.5 V, respectively.