Effect of conjugation length on photophysical properties of a conjugated–non-conjugated multiblock copolymer

The synthesis, structural characterization and photophysical properties of copolymers built by conjugated PPV type units of variable length and an aliphatic spacer are described. The aliphatic spacer provided good film forming capability and solubility. The effective conjugation extension was determined and its influence on the bandgap was evaluated, complementing theoretical and experimental data, since the PV units were oligomeric in size but with the mobility of longer chains. Aggregation phenomena were investigated; ground state dimers or higher associated forms were detected. The electrical and photovoltaic properties were studied in devices built with the neat polymers or containing a heterojunction with fullerene (C60), the photovoltaic responses were in agreement with the photoluminescence results. The most efficient photovoltaic device was based on the polymer containing the longest conjugated block, which also the most luminescent material.