Synthesis of dithieno[2,3-b:3',2'-d]thiophenes-building blocks for cross-conjugated beta-oligothiophenes

Syntheses of annelated and functionalized beta-trithiophenes (dithieno2,3-b:3',2'-d]thiophenes), building blocks for the helically annelated, cross-conjugated beta-oligothiophenes, are reported. UV-vis spectra reveal that the effect of octyl substituents on the onset of electronic absorption in annelated beta-trithiophenes is negligible compared to the effect of helical distortion in the higher beta-oligothiophenes.