The emission color of polyfluorenes can be turned over entire visible region by incorporating comonomer into polyfluorene backbone．In this paper

we demonstrate color tuning in polyfluorene derivatives by incorporating thiophene into the polyfluorene main chain．High molecular weight (Mn=6000～53000)

readily soluable copolymers of different compositions were prepared from 2

7-dibromo-9

9-dioctylfluorene (DOF)

2

7-bis(4

4

5

5-tetramethyl-l

3

2-dioxaborolan-2-yl)-9

9-dioctylfluorene and a narrow band gap comonomer 2

5-dibromothiophene using palladium catalyzed Suzuki coupling methods．The comonomer feed ratios of DOF to thiophene were 95:5

90:10

85:15

70:30 and 50:50 respectively．Theresulting copolymers are soluble in common organic solvents

such as THF and CHCl3．The actual molar ratios of DOF to thiophene in the copolymers were estimated by means of elemental analysis．The results indicate that the actual ratio of DOF to thiophene in the copolymer is very close to the feed ratio．The electrochemical

optical

photoluminescent (PL) and electroluminescent (EL) properties of the copolymers were studied．Cyclic voltammogram (CV) indicates that the LUMO level of the copolymers is close to that of the PF homopolymer

and it keeps almost constant for copolymers with different thiophene content．The HOMO level slightly decreases with increasing the thiophene content in the copolymer．PL and EL peaks ale red-shifting with increasing the thiophene content．The maximal EL emission wavelength of the copolymers is red-shifted from 490 nm to 541 nm

when the thiophene content increases from 5％ to 50％．Both PL and EL efficiencies decrease with increasing the thiophene content．The highest external EL quantum efficiency 0.45％ was obtained from the device at the thiophene ratio of 5％ and 10％

respectively．The results indicate that the use of conjugated polyfluorene as wide band-gap segment with a small amount (1％～5％) of narrow band-gap dopant in the molecular level could provide a new way to combine high quantum efficiency along with color turning ability．