The problem of long wavelength emission from ketone defects in polyindenofluorenes can be overcome by the introduction of aryl substituents which are much less susceptible to oxidation. A new polyindenofluorene with octylphenyl side chains has been prepared via a terphenyl intermediate. Unlike alkyl-substituted polyindenofluorenes, this displays stable blue emission in the solid state. Blue-emitting LEDs have been fabricated whose emission is stable at voltages below 10 V, with brightnesses of up to 125 cd/m(2) and efficiencies of up to 0.11 cd/A. Furthermore, no emission from ketone defects was detected even in devices run at voltages above 20 V.