Amino-containing saturated red light-emitting copolymers based on fluorene and carbazole units

Amino-containing copolymers were synthesized by Suzuki polycondensation based on 9,9-di(2-ethylhexy)fluorene, 9-dimethylaminopropyl carbazole and 4,7-di(4-hexyl-2-thienyl)-2,1,3-benzothiadiazole (≤15 mol%) units. The copolymers had high glass-transition temperature (Tgs: 86–145 °C), excellent thermal stability (Td (5% loss): 400 °C) and emitted red light at 658 nm. The peak was shifted from 614 to 658 nm when the 4,7-di(4-hexyl-2-thienyl)-2,1,3-benzothiadiazole content was increased from 0.1 to 15 mol%. The dimethylaminopropyl group in the side chain of the copolymer significantly lowered the barrier height of the interface between the metal cathode and the polymer. Thus, aluminium can be used as the cathode in polymer light-emitting devices and operated at a level of performance similar to that achieved with metal cathodes such as barium.