A series of low band-gap conjugated copolymers（PFO-DDQ） derived from 9

9-dioctylfluorene（DOF） and 2

3-dimethyl-5

8-dithien-2-yl-quinoxalines（DDQ） is prepared by the palladium-catalyzed Suzuki coupling reaction with the molar feed ratio of DDQ around 1%

5%

15%

30% and 50%.The obtained polymers are readily soluble in common organic solvents.The solutions and the thin solid films of the copolymers absorb light from 300～590 nm with two absorbance peaks at around 380 nm and 490 nm.The PL emission consists exclusively of DDQ unit emission at around 591～643 nm depending on the DDQ content in solid film.The EL emission peaks are red-shifted from 580 nm for PFO-DDQ1 to 635 nm for PFO-DDQ50.Efficient energy transfer due to exciton trapping on narrow-band-gap DDQ sites has been observed.The highest external quantum efficiency achieved with the device configuration ITO/PEDOT/PVK/PFO-DDQ15/Ba/Al is 1.33% with luminous efficiency 1.54 cd/A.Bulk heterojunction photovoltaic cells fabricated from composite films of PFO-DDQ30 copolymer and -phenyl C

6

1 butyric acid methyl ester（PCBM） as electron donor and electron acceptor

respectively in device configuration: ITO/PEDOT∶PSS/PFO-DDQ30∶PCBM/PFPNBr/Al shows power conversion efficiencies 1.18% with open-circuit voltage（V

o

c） of 0.90 V and short-circuit current density（J

s

c） of 2.66 mA/cm2 under AM 1.5 solar simulator（100 mW/cm2）.The photocurrent response wavelengths of the PVCs based on PFO-DDQ30/PCBM blends covers 300～700 nm.This indicates that these kinds of low band-gap polymers are promising candidate for polymeric solar cells and red light-emitting diodes.