Tuning Energy Levels and Film Morphology in Benzodithiophene-Thienopyrrolodione Copolymers via Nitrogen Substitutions

We report the synthesis of the benzo[1,2-d:4,5-d]bisthiazole-thieno[3,4-c]pyrrole-4,6-dione copolymer pBBTzTPD, a nitrogen-substituted version of the highly efficient organic photovoltaic donor copolymer benzo[1,2-d:4,5-d']dithiophene-thieno[3,4-c]pyrrole-4,6-dione pBDTTPD. This polymer was achieved via a novel and facile synthesis of 2,6-diaminobenzo[1,2-d:4,5-d']bisthiazoledione (1) using inexpensive and commercially available bromanilic acid and thiourea precursors in a one-pot two-step reaction. 1 can be easily converted to 2,6-dibromo-4,8-di(2-ethylhexyloxy)benzo [1,2-d:4,5-d']bisthiazole 6, which can then be copolymerized with n-octylthieno[3,4-c]pyrrole-4,6-dione (TPD) using direct arylation polymerization. The pBBTzTPD copolymer was characterized and compared with pBDTTPD in terms of molecular and electronic structure.