This thesis describes work towards a range of novel nitrogen containing polyaromatic heterocycles for use as organic semiconductors. A route to benzo[b]carbazole end-capped oligothiophenes has been developed; relying on two key steps; namely a connective-Pummerer cyclisation and a SmI2-mediated cleavage–cyclisation cascade. A route to extended dibenzoindolo[3,2-b]carbazole-based aza-heptacenes has also been developed, by employing the same key steps in a two-directional manner. The physical and electronic properties of the resulting materials has been assessed, and the utility of the materials in OFET devices has been demonstrated.