A series of random low band-gap conjugated copolymers (PFO-DDTQ) derived from 9,9-dioctylfluorene (DOF) and 6,7-dimethyl-4,9-di(4-hexylthien-2-yl)[1,2,5]thiadiazolo[3,4-g]quinoxali nes (DDTQ) are prepared by the palladium-catalyzed Suzuki coupling reaction. The obtained polymers are readily soluble in common organic solvents. The thin solid films of the polymers absorb light from 300 to 840 nm with two absorbance peaks at around 380 and 710 nm. Electroluminescent peaks are between 0.8 and 0.9 um based on the polymers. The maximal external quantum efficiency reaches 0.30% with the emission peak at 824 nm from PFO-DDTQ1 based devices. (C) 2008 Wiley Periodicals, Inc.