Planar 2,2′-bithiophenes with 3,3′- and 3,3′,4,4′-substituents. A computational study

Ab initio calculations have shown that when carbonyl groups are incorporated into the 3- and 3′-positions of bithiophenes, as part of five-membered rings, the bithiophene system is planar. This is due to electrostatic attraction between the carbonyl oxygen and the sulfur atom in the adjacent ring. In the analogous systems containing a CH2 group in place of the carbonyl, or containing six-membered rather than five-membered rings, the bithiophenes are twisted. This has implications for preparing planar polythiophenes.