Functional 4 H-Dithieno[3,2- b:2′,3′- d]pyrrole Derivatives in Base-Dopable Conjugated Polymers and Oligomers

A novel derivative of dithieno[3,2-b:2′,3′-d]pyrrole containing solubilizing side chains in the β-positions is reported and incorporated into a conjugated oligomer by a Pd-catalyzed direct arylation reaction. Following deprotection, a soluble conjugated oligomer was formed, in which the pyrrolic nitrogen was unsubstituted. Deprotonation upon exposure to tetrabutylammonium fluoride or hydroxide resulted in a large shift of the main absorption peak of 0.53 eV, from 425 to 520 nm, as a result of the delocalization of the resulting anion. Such changes were easily observable by the naked eye, and the pKa value of the pyrrolic group was calculated to be ∼15.9. The dithieno[3,2-b:2′,3′-d]pyrrole unit was also incorporated into an analogous polymeric system, which was partly deprotected under the same conditions as that of the conjugated oligomer. The resulting polymer was readily deprotonated in solution, resulting in a shift of the main absorption peak by 0.55 eV.