Communications ADVANCED MATERIALS[I21 As for (BET-TTF),X (X = SbF,, AsF,, PF,) salts [6] calculations where the outer five membered rings are replaced by two hydrogen atoms and all other geometrical details of the crystal structure are maintained show that most of the HOMO hand dispersion is associated with S,.. . Sj contacts. Consequently, even if it cannot be completely ruled out that the presence of small amounts of the Z isomer (see Scheme 1) can play some role in the observed structural disorder, the conductivity should not he noticeably affected by this fact.

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Previous calculations have suggested that the formation and the stability of charge transfer bonds in doped polyconjugated systems may be maximized by a favored topology of the dopant molecule. The preferred site of attack is found where the steric hindrance is minimized. Following these principles, regiospecific poly(3,3"-dihexyl-2,2':5',2"-terthiophene) was synthesized and doped with FeC13. The time and temperature dependence of the dedoping process has been studied by the analysis ofthe doping induced infrared spectrum.This material in the doped state shows an extremelygreat stability (in air, even at relatively high temperatures) never previously reported for any other doped system.