Regiochemical Effects of Sulfur Oxidation on the Electronic and Solid-State Properties of Planarized Oligothiophenes Containing Thieno[3,2-<i>b</i>]thiophene Units

The effect of position and degree of sulfur oxidation on the fundamental properties of a series of planarized thieno[3,2-b]thiophene S,S-dioxides derivatives was studied. The optical data reveal a red shift in the longest wavelength of absorption relative to the nonoxidized analogues that is indicative of a reduced HOMO−LUMO gap. The position of oxidation rather than the extent of oxidation is the most critical factor in controlling electronic properties. Single-crystal analysis reveals that some of the oligothiophene S,S-dioxides studied present π−π interactions which are completely absent in the nonoxidized analogue.