Synthesis of new alternating block copolymers with tailored π conjugated blocks and non conjugated aliphatic spacers The discovery of metal like conductivity in oxidized poly(acetylene) or shortly after in polyaromatic systems such as poly(pyrrole) poly(thiophene) or poly(aniline) in the late seventies and early eighties (1 6) has progressively generated a rich library of synthetic chemistry in the more general context of functional π conjugated systems. As for conductive polymers in general the synthetic chemistry of linearly π conjugated systems has developed considerably over the past twenty years and has greatly diversified in terms of objectives and methods. In 1990 the realization of the first electroluminescent devices in which a π conjugated polymer was used as a lumophore represents a turning point in the field of π conjugated systems (7 8). This discovery together with a parallel intensification of research on field effect transistors (9 10) photovoltaic cells based on π conjugated polymers and oligomers (11 13) nonlinear optical materials (14) plastic solar cells (15 19) and optically pumped lasers (20) contributed strongly to build up a different vision of linear π conjugated systems.