Radical cations of a soluble rigid tetrathienoacene are capable of forming stable π-dimer dications at ambient temperature when the short backbone becomes extended with conjugated thiophene-2-yl substituents in the α-positions. On the other hand, simple attachment of methyl groups on the α-carbon of the external thiophen-2-yl rings proved sufficient to inhibit the dimerization. Stable radical cations were also exclusively formed for tetrathienoacene derivatives end-capped with bulky TIPS and phenyl substituents.