Novel red-emitting fluorene-based copolymers

A series of novel soluble conjugated copolymers derived from 9,9-dioctylfluorene (DOF) and 4,7-di-2-thienyl-2,1,3-benzothiadiazole (DBT) were synthesized by a palladium-catalyzed Suzuki coupling reaction with different feed ratios of DOF to DBT. Owing to exciton confinement on the DBT site, exciton emission is centred on the DBT chromophore and gives rise to saturated red emission. Polyfluorene fluorescence is quenched completely at DBT concentrations as low as 1% in the solid film. Devices based on these copolymers emit a saturated red light. Chromaticity coordinates are around x = 0.70, y = 0.30 for the copolymers. The emission peaks are shifted from 628 nm to 674 nm when DBT content increases from 1 to 35%. The highest quantum efficiency achieved with device configuration of ITO/PEDT/PFO-DBT/Ba/Al was 1.4% for the copolymer with 15% DBT content.