The Preparation of 3,6-Bis(3-hexylthien-2-yl)-s-tetrazine and Its Conjugated Polymers

We demonstrated, for the first time, that 3,6-bis(3-hexylthien-2-yl)-s-tetrazine (TTz) with hexyl group at the 3-position of thiophene rings can be prepared using a modified sulfur-assisted Pinner synthesis. Although the hexyl group creates large steric hindrance to the tetrazine ring formation reaction, and the reaction under a traditional condition only produces trace amount of the target product, the yield of this reaction under a modified reaction condition using anhydrous hydrazine at 68 degrees C can reach 65%. Two new copolymers of the resulting TTz and hexyl-or 2-ethylhexyl-substituted cyclepenta-dithiophene have been prepared. The polymers show a broader light absorption in film than in solution attributing to the large distribution of effective conjugation length of polymer chain due to the existence of both cis- and trans-orientations of the 3-hexylthiophene units in the planar polymer chain in solid state. Although the polymers show a narrow band gap and a deep HOMO level, which are desirable for generating an efficient light absorption and a larger open circuit voltage (V-oc) of the resulting solar cell devices, the device performance is not as good as expected. It is attributed to the random distribution of the cis- and trans-conformations along the polymer chain. (C) 2011 Wiley Periodicals, Inc. (C) J Polym Sci Part A: Polym Chem 49: 3374-3386, 2011