Two novel series of soluble alternating conjugated copolymers comprising 10-alkylphenothiazine and bithiophene or 3-pentylthieno[3,2-b]thiophene moieties were synthesized using palladium-catalyzed Suzuki coupling reaction. The structures of the polymers and their thermal, photophysical, electrochemical, and photovoltaic properties were characterized and investigated. The polymers exhibited good thermal stability with decomposition temperature in the region of 342-390 degrees C and their glass transition temperatures (T,) ranging from 126 to 150 degrees C. All polymers demonstrate broad optical absorption in the region of 300-500 nm with efficient blue-green light emission. They showed ambipolar redox properties with low HOMO levels around -5.13 eV Polymer solar cells were fabricated using blends of the copolymers and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) in a 1:1 weight ratio. The maximum power conversion efficiency (eta = 0.24%) was measured for the poly[3,7- (10-hexylphenothiazine)-alt-bithiophenel as donor under simulated sun light (1000 W/m(2)). Open circuit voltages of up to 0.8 V have been obtained. (c) 2007 Wiley Periodicals, Inc.