Molecular structure of a novel heterocycle: 1,1,4,4,tetramethyl-1 H,4 H-thieno[3,4-c]thiophene

The X-ray crystal structure of the title compound, C₁₀H₁₄S₁, is reported. Crystals are monoclinic, space group P2₁/c with Z = 2 in a unit cell of dimensions a = 8.517(2), b = 6.109(1), c = 10.730(1) Å, and β = 107.01(2)°. The structure was solved by direct methods and refined by full-matrix least squares to R = 0.032 for 1059 diffractometer data. The bicyclic molecular framework contains eight π-electrons and is planar and rigid, all relevant interatomic distances corresponding to either ideally single or ideally double bonds. The first UV absorption observed at 3.61 eV, and tentatively described as due to a π(b_g) → π*(a_u*) electron transition, is significantly higher than that found in a related aromatic tetraphenylthienothiophene system.