Conjugated Ladder-Type Heteroacenes Bearing Pyrrole and Thiophene Ring Units: Facile Synthesis and Characterization

Ladder-type heteroacenes containing pyrrole and thiophene rings, dibenzo[b,b′]thieno[2,3-f:5,4-f′]-carbazoles (DBTCZ, 1), and diindolo[3,2-b:2′,3′-h]benzo[1,2-b:4,5-b′]bis[1]benzothiophene (DIBBBT, 2), were facilely synthesized through proper precursors (7, 11, and 18) respectively. The key step is a triflic acid induced intramolecular electrophilic coupling reaction of corresponding aromatic methyl sulfoxides with activated aromatic building blocks, which enables regioselective ring closure. Both precursors (7 and 11) toward DBTCZ gave the symmetrical product but with solubilizing alkyl chains in two different fashions. DIBBBT was also synthesized as the extended ladder-type heteroacene with defined structure. These obtained heteroacenes are fully characterized (mass spectrometry, NMR, elemental analysis), and their X-ray analysis and optical and electrochemical properties are reported.