Organic tunable electroluminescent diodes from polyfluorene derivatives

We report on the electroluminescent properties of recently synthesized fluo rine-based pi -conjugated polymers. The spectral emission varies from blue to yellow depending on the composition of the alternated copolymers contain ing thiophene or phenylene moieties. The luminance of the devices can be en hanced by adequate balancing of the hole and electron injection/transport. Incorporation of a hole transporting molecule in the polymer and insertion of an insulating buffer layer in the device resulted in enhancement of the luminous efficiency. A 30-fold enhancement of the luminance was obtained by inserting an electron transporting layer. The highest luminance reached wa s 1640 cd/m(2) at 17 V and was obtained with a green emitter, poly(2,2 '-(5 ,5 ' -bithienylene)-2,7-(9,9-dioctylfluorene)) (PBTF). (C) 2001 Elsevier Sc ience B,V, All rights reserved.