Synthesis, characterisation and application in electronic devices of low band gap materials based on thiophene derivatives

Recent years have seen the increased use of organic materials for electronic applications as photovoltaic cells and field-effect transistors (FETs). Such applications require the use of conjugated polymers with a sufficiently high quality, purity and molecular weight (M_w > 30 000). This dissertation deals with the search for possible synthetic routes leading to low band gap (LBG) materials, conjugated polymers with a small energy gap between the valence and conduction band. Those materials show interesting properties which make them extremely attractive for applications in plastic electronics. The processability of these materials here is very important. This can be obtained either by introducing long chains or by the use of a precursor route. In this dissertation especially the latter is dealt with. Here first a soluble precursor polymer is synthesised which, after thermal treatment, gives rise to the conjugated polymer.; In the synthesis of soluble low band gap materials by introducing long tails on the monomer unit, especially the synthesis and characterisation of soluble poly(isothianaphthene) (PITN) derivatives, obtained via the thermal and non-oxidative polymerisation of 5,6-disubstituted dithiophthalides, is discussed. 3,4-Dihalo substituted poly(thienylene vinylene) (PTV) derivatives were synthesised via the sulphinyl and xanthate precursor route. Whereas the use of the sulphinyl precursor route was limited to electron poor derivatives, the xanthate route could be used in the synthesis of both electron poor and electron rich derivatives. Previous research indicated that the use of the sulphinyl precursor route was problematic for the synthesis of PTV. For this reason, the use of the xanthate route was valorised. We did not only highlight the synthesis and characterisation of precursors with the commonly used O-ethyl xanthate group, also new xanthate monomers were synthesised and polymerised. In the end also a total new precursor route, the dithiocarbamate route, is presented. Trials to polymerise the monomers to obtain precursors of poly(p-phenylene vinylene) (PPV) and PTV were successful. Not only the yields were good but the obtained polymer also had improved properties compaired to the same polymers obtained via the xanthate precursor route. This indicates that this new precursor route is an improved version of the xanthate route and therefore it is interesting to look more into detail in the scope and limitations of this route.; In general, we aimed at efficient synthetical pathways in order to obtain well defined polymer materials. In cooperation with other research groups, different materials were characterised en tested with an eye to further applications in transistors and solar cells.