title: Terthiophene
text: # Terthiophene
  
  Terthiophene is the organic compound with the formula $[C_4H_3S]_2C_4H_2S.$ It is an oligomer of the heterocycle thiophene, a shorter oligomer is dithienyl, and the parent polymer is polythiophene. In the most common isomer of terthiophene, two thienyl groups are connected via their 2 positions to a central thiophene, also at the carbon atoms flanking the sulfur.
  
  ## Preparation of terthiophene
  
  Terthiophene is prepared by the nickel- or palladium-catalysed coupling reaction of 2,5-dibromothiophene with the Grignard reagent derived from 2-bromothiophene.
  
  ## Properties and applications
  
  This isomer is a pigment in African marigolds (Tagetes spp.) and exhibits some biological activity because it sensitizes the formation of singlet oxygen. It is responsible for the insecticidal activity of Tagetes minuta.
  
  Together with derivatives of 2,2'-bithiophene, various substituted terthiophenes occur naturally. Examples include 5,5''-dichloro-α-terthiophene, 5-chloro-α-terthiophene, 5-acetyl α-terthiophene, and 5-carboxyl bithiophene.
  
  Terthiophene has been employed as building block for the organic semi-conductor polythiophene.
  
  