Examples of the Direct Arylation Polycondensation

The first example of synthesis of poly(3-alkylthiophene)s by direct arylation was reported in 1999. Recently, the syntheses of high molecular weight poly(fluorene-aZt-tetrafluorobenzene), poly(fluorene-aZt-dithiophene), and poly(thienopyrroledione-aZZ-dithiophene) by direct arylation were published. Here, we provide a few examples to show the use of direct arylation to synthesize low bandgap conjugated polymers that are promising donor materials for PSCs. 

2 -bithiophene-based monomer has more than one type of reactive C-H bond, although reactions typically occur in the 5- and 5 -positions first. Attempts to copolymerize 2,2-bithiophene with dibromo compound rendered materials with low solubility due to cross-linking in the 3,3 - and 4,4 -positions of the bithiophene monomer. To evade these side reactions, the other reactive C-H bonds on the thiophene monomers were blocked with methyl groups. P37 and P38 were synthesized by direct heteroarylation polymerization. However, the film absorption onsets were hypsochromically shifted compared to the unprotected bithiophene analogs. The methyl groups indeed cause twisting in the polymer backbone and disrupt conjugation. 

A D-A conjugated polymer, P39, with a of 41 kDa was synthesized by Heeger et al. using a direct heteroarylation procedure. A relatively high PCE of over 6% was obtained from BHJ solar cells based on a photoactive film 

Cheng and S. A. Chen, Fullerene Derivative-Doped Zinc Oxide Nanofilm as the Cathode of Inverted Polymer Solar Cells with Low-Bandgap Polymer (PTB7-Th) for High Performance, Adv. Mater., 2013, 25(34), 4766-4771. 

Mercier and M. Leclerc, Direct (Hetero)Arylation A New Tool for Polymer Chemists, Acc. Chem. Res., 2013, 46(7), 1597-1605. 

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