Regiospecifically alkylated oligothiophenes via structurally defined building blocks

We have developed a new synthetic protocol for the unsymmetrically alkylated and halogenated terthiophenes 5 and 10. To demonstrate their usefulness as building blocks for well-defined oligothiophenes, we synthesized a series of seven new sexi-, septi- and octithiophenes. Terthiophene 5 could be dimerized to the didecylsexithiophene In6 and terthiophene 10 to sexithiophene Out6, respectively, by the use of nickel catalysis. Together with the bis-stannylated thiophenes 11 and 12, the septithiophenes In7 and Out7 as well as the octithiophenes In8 and Out8 could be obtained via Stille coupling methodology. We could also obtain the unsymmetrical sexithiophene Unsym6 by selective heterocoupling between one equivalent of terthiophene 5 and 10 each. All new sexi-, septi- and octithiophenes show high photoluminescence in solution, but the quantum yield drops sharply in thin films of the materials.