Synthesis and Color Tuning of Poly(p-phenylenevinylene) Containing Terphenyl Units for Light Emitting Diodes

摘要

New PPV based conjugated polymers,containing terphenyl units,were prepared as the electroluminescent (EL) layer in light-emitting diodes (LEDs).The prepared polymers,poly[2,5-bis(4-(2-etylhexyloxy)phenyl)-1,4-phenylenevinylene] (BEHP-PPV),poly[2-(2-ethylhexyloxy)-5-(4-(4-(2-etylhexyloxy)phenyl)phenyl)-1,4-phenylenevinylene] (EEPP-PPV) and poly[2-(2-ethylhexyloxy)-5-(9,9-bis(2-etylhexyl)fluorenyl)-l,4-phenylenevinylene] (EHF-PPV),were soluble in common organic solvents and used as the EL layer in double layer light-emitting diodes (LEDs) (ITO/PEDOT/polymer/Al).The polymers were prepared by the Gilch reaction.The number-average molecular weight (M_n),weight-average molecular weight (M_w),and the polydispersities (PDI) of these polymers were in the range of 9000-58000,27000-231000,2.9-3.9,respectively.These polymers have quite good thermal stability with decomposition starting above 320-350.The polymers show photoluminescence (PL) with maximum peaks at around 526-562 nm (exciting wavelength,410 nm) and blue EL with maximum peaks at around lambda_(max) = 526-552 nm.The current-voltage-luminance (I-V-L) characteristics of polymers show turn-on voltages of 5 V.Even though both of EEPP-PPV and BEHP-PPV have the same terphenyl group in the repeating unit,EEPP-PPV with directly substituted alkoxy group in the back bone has longer effective conjugation length than BEHP-PPV,and exhibits red shift in the PL spectra.Both of EEPP-PPV and EHF-PPV have ter-phenyl units and directly substituted alkoxy group in back bone.EHF-PPV with fluorenyl unit attached to the PPV backbone has shorter effective conjugation length than EEPP-PPV with biphenyl unit,and exhibits blue shift in the PL spectra.