Organic semiconducting oligomers containing three to nine heterocyclic units and based on 1,4-dimethoxybenzene, thiophene and thiazole have been studied by DFT and TDDFT at the B3LYP/6-31G(d,p)  level.  The energy  of  each  molecule,  those  of  the frontier orbitals  HOMO and  LUMO,the width  of  the  band  gaps  and  the  optical  properties ...