Dialkyl-Substituted Thieno[3,2-b]thiophene-Based Polymers Containing 2,2‘-Bithiophene, Thieno[3,2-b]thiophene, and Ethynylene Spacers

A series of 3,6-dinonylthieno[3,2- b ]thiophene-based polymers containing either 2,2‘-bithiophene, thieno[3,2- b ]thiophene, or ethynylene spacer units were synthesized by Stille and oxidative coupling reactions. Their electronic properties were studied by UV−vis absorption and fluorescence spectroscopies in solution and in the solid state and compared to poly(3,6-dinonylthieno[3,2- b ]thiophene). The introduction of these spacers led to a substantial red shift in the longest wavelength of absorption, indicating that these modifications restore, to a significant extent, the planarity of the system resulting in increased conjugation. Model compounds representing the basic structural unit of each polymer were synthesized, and computations were performed to understand the role of the spacer in dictating the conformation of the polymer backbone.