Structure optimizations of the thiophene carbon-sulfur H 2 (C 2 S) n C 2 H 2 (n = 1-20) were carried out using density functional theory calculations at the B3LYP/ 6-31G(d) level. The B3LYP/6-31G(d) geometrical data for heptamer H 2 (C 2 S) 7 C 2 H 2 and undecamer H 2 (C 2 S) 11 C 2 H 2 are in good agreement with the X-ray crystallographic data for the helical (C 2 S) n b-heptathiophene and b-undecathiophene, respectively. Structural and electronic properties of helical oligothiophenes obtained at the B3LYP/6-311??G(d,p)//B3LYP/6-31G(d) level are reported. The strain energy formula of n oligothiophenes as a linear function of their molecular length was obtained.