The Collaborative International Dictionary of English v.0.48:

Thiophthene \Thi*oph"thene\, n. [Abbreviated from
   thionaphthene.] (Chem.)
   A double thiophene nucleus, C6H4S2, analogous to
   thionaphthene, and the base of a large series of compounds.
   [Written also thiophtene.]
   [1913 Webster]