Mixed-Ligand Approach to Palladium-Catalyzed Direct Arylation Polymerization: Synthesis of Donor–Acceptor Polymers Containing Unsubstituted Bithiophene Units

• Published in: Macromolecules 2020-01, Vol.53 (1), p.158-164
• Main Authors: Wakioka, Masayuki, Morita, Hazuki, Ichihara, Nobuko, Saito, Masahiko, Osaka, Itaru, Ozawa, Fumiyuki
• Format: Article
• Language: English
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/acs.macromol.9b02298

The combined use of P­(2-MeOC6H4)3 (L1) and TMEDA as ligands effectively prevents defect formation in palladium-catalyzed direct arylation polymerization (DArP) to give donor–acceptor type alternating copolymers (DA polymers) with unsubstituted 2,2′-bithiophene units. When only L1 is used as a ligand, the reaction of 5,6-difluoro-4,7-bis­[5-bromo-4-(2-octyl­dodecyl)­thiophene-2-yl]­benzo­[c]­[1,2,5]­thiadiazole (1a-Br) with 2,2′-bithiophene (2-H) in toluene at 100 °C forms a notable amount of insoluble materials via branching and cross-linking. In contrast, in the presence of L1 and TMEDA, the formation of insoluble materials is completely suppressed, and PffBT4T [poly­(1a-alt-2)] with a well-controlled structure and high molecular weight is obtained (M n = 88100). Similarly, the reaction of 5,10-bis­[5-bromo-4-(2-decyltetra­decyl)­thiophene-2-yl]­naphtho­[1,2-c:5,6-c′]­bis­[1,2,5]­thiadiazole (1b-Br) with 2-H in toluene at 110 °C forms PNTz4T[poly­(1b-alt-2)] with M n = 43800. The resulting polymers function as good components of bulk-heterojunction type organic solar cells (OSCs) using PC71BM. In particular, PNTz4T performs the best of all the DArP polymers reported so far (PCE = 9.0(1)%).