Paper of the week: Direct heteroarylation of β-protected dithienosilole and dithienogermole monomers

Conjugated polymers have been used extensively in organic electronic devices such as bulk heterojunction solar cells (BHJ-SCs), light emitting diodes (LEDs), field effect transistors (FETs), etc. Typical synthetic protocols involve conventional aryl carbon–carbon bond forming reactions, including Stille, Suzuki, Negishi, etc., where a (hetero)aryl halide is coupled with a (hetero)aryl organometallic reagent. Although widely utilized, these commonly utilized reactions are hampered by stoichiometric amounts of organometallic waste as well as unstable monomers. A greener alternative is direct (hetero)arylation, which has been used extensively in the preparation of small molecules, and involves the coupling of an aryl halide directly with another arene through activation of a C–H bond. However, this reaction is not selective and more than one type of C–H bond may react, which, during polymerization reactions, can lead to cross-linked materials.

Graphical abstract: Direct heteroarylation of β-protected dithienosilole and dithienogermole monomers with thieno[3,4-c]pyrrole-4,6-dione and furo[3,4-c]pyrrole-4,6-dione

In their paper, Leclerc and co-workers reported the preparation of N-octylthieno[3,4-c]pyrrole-4,6-dione with 4,4-bis(2-ethylhexyl)-dithieno[3,2-b:2′,3′-d]silole (PDTSiTPD) and 4,4-bis(2-ethylhexyl)-dithieno[3,2-b:2′,3′-d]germole (PDTGeTPD), which have exhibited high efficiencies in organic solar cells, using direct (hetero)arylation polymerization methodologies. In order to circumvent side reactions leading to cross-linked polymers, a number of new dithieno[3,2-b:2′,3′-d]silole (DTSi) monomers were prepared where the β-positions were blocked with alkyl chains and the alkyl groups on the heteroatom were modified. Co-polymers were synthesized with N-alkylthieno[3,4-c]pyrrole-4,6-dione (TPD) and the oxygen congener, N-alkylfuro[3,4-c]pyrrole-4,6-dione (FPD).

Direct heteroarylation of β-protected dithienosilole and dithienogermole monomers with thieno[3,4-c]pyrrole-4,6-dione and furo[3,4-c]pyrrole-4,6-dione by Lauren G. Mercier, Badrou Réda Aïch, Ahmed Najari, Serge Beaupré, Philippe Berrouard, Agnieszka Pron, Amélie Robitaille, Ye Tao and Mario Leclerc Polym. Chem. 2013, 4, 5252-5260.

This article is part of the Polymer Chemistry themed collection on Conjugated polymers.

Julien Nicolas is a guest web-writer and advisory board member for Polymer Chemistry. He currently works at Univ. Paris-Sud (FR) as a CNRS researcher.

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