Two novel alternating pi-conjugated copolymers, poly[2,8-(6,6',12,12'-tetraocty1-6,12-dihydroindeno41,2bffluorene-ait-5(1-(2,6-diisopropylphenyl)-2,5-di(2-thienyl)pyrrole) (P1) and poly[2,8-(6,6',12,12'-tetraocty1-6,12-dihydroindeno-[1,2blfluorene-a/t-5(1-(p-octylphenyI)-2,5-di(2-thienyl)pyrrole) (P2), were synthesized via the Suzuki coupling method and their optoelectronic properties were investigated. The resulting polymers P1 and P2 were completely soluble in various common organic solvents and their weight-average molecular weights (M,) were 5.66 x 10(4) (polydispersity: 1.97) and 2.13x 10(4) (polydispersity: 1.54), respectively. Bulk heterojunction (BHJ) solar cells were fabricated in ITO/PEDOT:PSS/polymer:PC70BM(1:5)/TiOx/A1 configurations. The BHJ solar cell with P1:PC70BM (1:51 has a power conversion efficiency (PCE) of 1.12% (Jsc= 3.39 mA/cm2, t/o -= 0.67 V-oc = 49.31%), measured using AM 1.5 G solar sim- ulator at 100 mW/cm(2) light illumination. We fabricated polymer light-emitting diodes (PLEDs) in ITO/PEDOT:PSS/emitting polymer:polyethylene glycol (PEG)/Ba/A1 configurations. The electroluminescence (EL) maxima of the fabricated PLEDs varied from 526 nm to 556 nm depending on the ratio of the polymer to PEG. The turn-on voltages of the PLEDs were in the range of 3-8 V depending on the ratio of the polymer to PEG, and the maximum brightness and luminance efficiency were 2103 cd/m2 and 0.37 cd/A at 12 V, respectively. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3169-3177, 2010