A series of polythiophenes doped with dithieno[3,2-b:2',3'-d]phosphole units at varying levels (0-17%) were synthesized and characterized. Polymer work up provided two series of polymers from chloroform (C) and hexanes (H) for each doping level, respectively. Systematic structure property studies revealed that the C-series polymers generally had higher molecular weights than the H-series, but also slightly higher relative dithienophosphole concentrations, both having a significant impact on the photophysical and electrochemical properties of the polymers. Furthermore, the presence of the dithienophosphole units also stabilizes the LUMO levels, whereas the HOMO levels remain dominated by the thiophene units, resulting in desirable electronics for an interaction with acceptor materials, such as 1-(3-methoxycarbonyl)propyl-1-phenyl[6,6]C-61. Importantly, increasing amount of dithienophosphole doping results in increased conductivities for the polymers in their oxidized state, while concurrently significantly stabilizing the neutral polythiophenes toward oxidation under environmental conditions. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 1201-1209, 2011