Preparation and Luminescence Properties of Polymers Containing Dialkoxyacenes

Derivatives of 2,3-(1,4-dialkoxyaceno)norbornadiene 1 -4 underwent ring-opening metathesis polymerization (ROMP) reactions with a ruthenium carbene complex Cl2 (PCy3)2Ru=CHPh to afford the corresponding polymers P1-P4 with narrow polydispersity. These materials exhibited luminescence both in solution and as films, whereas P3 and P4 were used successfully for the fabrication of light emitting diodes (LED). The device ITO/P4/Ca/Al, made of a spin-coated layer of P3 or P4, displayed white light that can be turned on at 7 V with a maximum intensity of 427 cd/m2 at 15 V. The white electroluminescence is composed of a blue emission band from the aromatic chromophore and a red component derived from solid aggregates. The performance of devices can be improved by insertion of an additional electron-transporting layer, i.e., 1,3,5-tris(2ʹ-(1ʹ-phenyl-1ʹ-H-benzimidazole)benzene (TPBI). The device ITO/P4/TPBI/Mg:Ag displayed blue light with a turn-on voltage of 5 V and maximal intensity of 930 cd/m2 at 15 V. The change of chromaticity can be ascribed to a shift of charge recombination sites in the bulk of P4 film. The phenomenon was verified by adjusting the thickness of TPBI layer, whereas a continuous variation in color was observed upon changing bias.