An amphiphilic multiblock copolymer comprising nearly monodisperse poly(ethylene oxide) segments (M-w/M-n = 1.03) and polydisperse poly(methylphenylsilane) (PMPS) segments (M-w/M-n = 2.0) forms a variety of well-defined morphologies such as vesicles, micellar rods, and helices upon aggregation in water-based solvent systems, despite this polydisperse character. Since polysilanes show sigma -conjugation in the main chain, the optical and electronic properties of the described block copolymer depend on its confomational behavior. It is demonstrated by microscopic and spectroscopic techniques that the conformations of the PMPS backbone can be controlled through manipulation of the aggregation behavior, i.e., by the choice of the solvent composition.