NOVEL RED LIGHT-EMITTING POLYMERS BASED ON 2,7-CARBAZOLE AND THIOPHENE DERIVATIVES

A series of conjugated copolymers derived from 9-ethylhexyl-2,7-carbazole (Cz) and 4,7-di(4-hexylthien-2-yl)-2,1,3-benzothiadiazole (DHTBT) was synthesized by Suzuki polycondensation. The photo- and electro-luminescentproperties of these polymers were investigated. Efficient energy transfer from the Cz segment to the DHTBT unit occurseven if the DHTBT content as low as 1 mol%. PL emission was red-shifted significantly from 645 nm to 700 nm with theincrease in DHTBT content by 1-50 mol%. PL efficiencies decreased with the increase in DHTBT content in the polymersfrom 55% for PCzDHTBT1 gradually down to 7% for PCzDHTBT50. EL emission of these polymers red-shifted from640 nm to 690 nm when the DHTBT content increased from 1 mol% to 50 mol%. The highest external quantum efficiencywas 1.67% for PCzDHTBT25 with the maximum luminescence of 870 cd/m,'2 in the device configuration of ITO/PEDOT:PSS/polymer/PFN/Ba/Al. The enhancement of device performances could be due to the improved electron injection byinserting the amino-containing polyfluorene (PFN) layer. These polymers are promising candidates as a red emitter in thefull-color polymer light emitting diodes (PLEDs).