This work reports the properties of two types of thiophene-containing poly(arylene-ethynylene)-alt-poly(arylene-vinylene)s polymers, whose repeating units (-Ph-C equivalent to C-Th-CH=CH-Ph-CH=CH-)(n), 1, and (-Th-C equivalent to C-Ph-C equivalent to C-Th-CH=CH-Ph-CH=CH-)(n), 2, consist respectively of a 1: 2 and a 2:2 ratio of -C equivalent to C-/-CH=CH- moieties. Although similar electrochemical data (HOMO: -5.43 eV, LUMO: similar to - 3.15 eV, E-g(ec)=2.28 eV) as well as identical thin film absorption behaviour (lambda(a)=501 nm, E-g(opt)=2.10 eV) were obtained for both types of materials, significant differences in their thin film photoluminescence behaviour and photovoltaic properties were observed. While polymer I shows a fluorescence maximum at lambda(e)=568 nm (with a fluorescence quantum yield of Phi(f)=7%), a total fluorescence quenching was observed in 2. Solar cells (set up: ITO/PEDOT: PSS/active layer/LiF/Al; active layer consisting of I or 2 as donor and PCBM as acceptor in a 1: 3 ratio by weight) designed from 1 (best cell: V-OC = 900 mV, I-SC = 2.51 mA.cm(-2), FF=53.7%, eta(AM1.5)=1.21%) show far better photovoltaic performance than those from 2 (best cell: V-OC = 500 mV, I-SC = 1.44 mA.cm(-2), FF=37.1%, eta(AM1.5)=0.27%). (c) 2006 Elsevier B.V. All rights reserved.