Novel Poly(p-phenylenevinylene)s Derivatives with CF_3-Phenyl Substituent for Light-Emitting Diodes

摘要

New PPV derivatives which contain electron-withdrawing trifluoromethyl (CF_3) group,poly[2-(2-ethylhexyl-oxy)-5-(4-trifluoro methylphenyl)-l,4-phenylenevinylene] (EHCF3P-PPV),and poly[2-(2-ethylhexyloxy)-5-(3,5-bis(trifluoromethyl)-phenyl)-l,4-phenylenevinylene] (EHBCF_3P-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_3P-PPV (2.8,5.1 eV) and EHBCF_3P-PPV (3.0,5.3 eV) were lower than those of known poly[2-(2-ethylhexyloxy)-5-phenyl-l,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_3P-PPV,and EHBCF_3P-PPV show maximum photoluminescence (PL) peaks at gamma_(max) = 550,539 nm,and maximum EL peak at gamma_(max) = 545,540 nm,respectively.The current-voltage-luminance (I-V-L) characteristics of the polymers show that turn-on voltages of EHCF_3P-PPV and EHBCF_3P-PPV are around 4.0 and 3.5 V,respectively.