Synthesis of dithieno[2,3-b:3′,2′-d]thiophenes - Building blocks for cross-conjugated β-oligothiophenes

Syntheses of annelated and functionalized β-trithiophenes (dithieno[2,3-3′,2′-i/]thiophenes), building blocks for the helically annelated, cross-conjugated β-oligothiophenes, are reported. UV-vis spectra reveal that the effect of octyl substituents on the onset of electronic absorption in annelated β-trithiophenes is negligible compared to the effect of helical distortion in the higher β-oligothiophenes.