Synthesis, Structures, and Properties of Disubstituted Heteroacenes on One Side Containing Both Pyrrole and Thiophene Rings

A new series of ladder-type heteroacenes containing both pyrrole and furan rings, 5,6-disubstituted diindolo[3,2-b:4,5-b′]thiophenes (DITs), were effectively synthesized from N-functionalized 3,3′-dibromo-2,2′-biindoles undergoing intramolecular cyclization with bis(phenylsulfonyl) sulfide and organolithium. Single-crystal X-ray results demonstrate that 5,6-dipropyldiindolo[3,2-b:4,5-b′]thiophene (4b) forms a herringbone-type of packing motif and 5,6-di(p-tolyl)diindolo[3,2-b:4,5-b′]thiophene (4d) forms a parallel packing motif. Both of them have S−S contacts, enhancing the electronic transport between molecules. Their photophysical properties suggest that the skeleton of diindolo[3,2-b:4,5-b′]thiophene is more favorable to aggregate in solid than that of indolo[3,2-b]carbazole. The large band gaps and low-lying HOMO energy levels could result in much better stability.