Synthesis and structure of alkyl-substituted fused thiophenes containing up to seven rings

We have established a series of synthetic methods to synthesize alkyl-substituted fused thiophenes with degrees of fusion from two to seven rings. These fused thiophene ring compounds have very good solubility in common organic solvents, making possible the solution processing of these compounds for electronic applications. The UV absorption of these fused thiophenes is blue-shifted when compared with their hydrocarbon counterparts. The larger band gaps result in much better stability. Single-crystal X-ray results for 3,6-didecanyldithieno2,3-d:2',3'-d']thieno3,2-b:4,5-b']dithiophene (FT5) and 3,7-didecanylthieno3,2-b]thieno2',3':4,5]thieno2,3-d]thiophene (FT4) demonstrate that both compounds form pi-stacking structures instead of a herringbone-type of packing motif. This more favorable pi-stacked structure may lead to better material electronic properties such as mobility in devices fabricated with these compounds.