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. (C) 2003 Elsevier Science Ltd. All rights reserved.