Selenophene and fluorene based narrow band gap copolymers with Eg = 1.41 eV for near infrared polymer light emitting diodes

A series of random low band-gap conjugated copolymers (PFO-DDSTQ) derived from 9,9-dioctylfluorene (DOF) and 6,7-dimethyl-4,9-di(selenophen-2-yl)-[1,2,5]thiadiazolo[3,4-g]quinoxaline (DDSTQ) are prepared by the palladium-catalyzed Suzuki coupling reaction. The obtained polymers are readily soluble in common organic solvents. The polymers absorb light from 300 to 880 nm with two absorbance peaks at around 370 and 740 nm. The optical band gaps of the resulting polymers with 15 or 30% narrow band-gap units in the polymer backbone calculated from the absorption onset are around 1.41 eV. The electroluminescent properties of the polymers were investigated and it was found that with 5% DDSTQ copolymerized on the main chain, the resulting polymer PFO-DDSTQ5 exhibited an exclusively near-infrared emission at 860 nm.