Synthesis and Electro-Optical Properties of Carbazole Containing Copolymers with Different Conjugated Structures for Polymer Light-Emitting Devices

Abstract

New copolymers such as Poly(9-(4-(2-ethyl-hexyloxy)-3,5-dimethylphenyl)carbazole-alt-aminonaphtalene) [P1] and Poly(4-(bis-methylbiphenyl-alt-9H-carbazol-9-yl)benzenamine) [P2] with chromophores separated by non-conjugated methylene spacers, and Poly(4-(dioctylfluorene-alt-9H-carbazole-9yl)benzenamine) [P3] based on alternating fluorene and amine units in the polymer backbone were synthesized by palladium catalyzed polycondensation reaction. Optical properties of these polymers were characterized in terms of UV/visible absorption and photoluminescence (PL) emission in solution and film state. Maximum PL emission (max,PL) of synthesized copolymers were observed in the blue region of 426nm-460nm in solution state, but the three polymers all showed large red shift in film state with the green emission. The electro-optical properties of these polymers in polymer light-emitting diode (PLED) devices were investigated from the viewpoint of utilizing the new polymers as emitting layer and hole injection/transport layer. The polymer P3 was found to function both as hole injection and hole transport layer with performance better than that of well known PEDOT:PSS hole injection layer material