Synthesis and Properties of Random Carbazole/1,3,4-Oxadiazole/Aniline Copolymers for Organic Light-Emitting Devices

Random copolymers, poly[(M1-M2)-ran-(M1-M3)], have been synthesized by N-(3,6-dibromo)carbazole (M1), aniline (M2) and 2-p-methylphenyl-5-(4-aminophenyl)-1,3,4-oxadiazole (M3). The random copolymers were obtained with high solubility and good film forming properties. Optical properties of these copolymers were investigated. As increasing the content of M3, the maximum absorption peaks (max,UV) of copolymers at 360nm increased gradually, which was the typical max,UV of poly(M1-alt-M3). Compared with maximum photoluminescence emission peak (max,PL) at 452nm of poly(M1-alt-M2), all the random copolymers displayed max,PL at about 519nm, similar with that of poly(M1-alt-M3). It was notable that max,PL of the random copolymers shifted to that of poly(M1-alt-M3) with the addition of M3 in the copolymers, and then remained almost unchanged irrespective of further increasing the content of M3, implying the emission from the lower band gap segment of poly(M1-alt-M3). The band gap energy of the copolymers was measured in the range of 2.822.91eV, and HOMO energy in the range of-4.95-5.11eV. Hole transporting properties of the synthesized copolymers in OLEDs were measured with the configuration of ITO/copolymer/Alq3/LiF/Al, where Alq3 was used as an emitting layer. It appeared that the random copolymers (P4P5) with the compositions of M1:M2:M3 (10:4:610:6:4 mole ratio) showed better hole-transporting property.