SYNTHESIS AND UV-VISIBLE PROPERTIES OF SOLUBLE REGIOREGULAR OLIGO(3-OCTYLTHIOPHENES), MONOMER TO HEXAMER

A series of head to tail alkyl-substituted oligothiophenes was synthes ized by a stepwise synthesis based on the repetitive use of the Suzuki coupling reaction between a stable thienyl boronic ester and the appr opriate chloride-protected precursors catalyzed by Pd[P(C6H5)(3)](4), under mild conditions. By this method, a very high level of regiospeci ficity was achieved, as shown in the synthesis of the dimer 3,4'-dioct yl-5'-chloro-2,2'-bithiophene, where no regioisomers could be detected . From the thus obtained chlorinated oligomers, free-ends oligo(3-octy lthiophenes) were synthesized by reductive dehalogenation. UV-visible properties were investigated in solution, and the absorption energy wa s found to depend linearly on the reciprocal of the number of thiophen e units. A comparison with the properties of analogous regioregular po ly(3-octylthiophenes) gave information on the structure of such polyme rs in solution.