Oligothiophenes S,S-dioxides. Synthesis and electronic properties in relation to the parent oligothiophenes

Oligothiophene S,S-dioxides from dimers to pentamers were obtained in good yields by reaction of mono- and dibrominated thiophene S,S-dioxides with the appropriate thienyl stannanes in the presence of Pd(AsPh3)4 generated in situ. The reaction rate with brominated thiophene S,S-dioxides is greatly accelerated compared to that employing thienyl bromides to obtain the parent oligothiophenes. HF/6-31G*ab initio calculations on 2,2¢-bithiophene and the corresponding monoand bis-S,S-dioxides show that the functionalization of the thienyl sulfur to the S,S-dioxide does not affect the ð,ð* nature of the frontier orbitals, decreases the energy of the LUMO much more than that of the HOMO, increases the degree of planarity of the molecular skeleton, and leads to higher syn anti rotation barriers about the carbon-carbon bond.