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.

Terthiophene is prepared by the nickel- or palladium-catalysed coupling reaction of 2,5-dibromothiophene with the Grignard reagent derived from 2-bromothiophene.

[2] This isomer is a pigment in African marigolds (Tagetes spp.)

and exhibits some biological activity because it sensitizes the formation of singlet oxygen.

[5] Terthiophene has been employed as building block for the organic semi-conductor polythiophene.