Closing the zipper: A method for the bottom-up organic synthesis of defect-free graphene nanoribbons in solution has been developed. Polyphenylene precursors with a unique kinked backbone enabled full cyclodehydrogenation in a single reaction step by an intramolecular Scholl reaction with FeCl
General polymerization procedure:
In a 35 ml microwave vial a mixture of the dihalogenated monomer (2.42 mmol) and the
diboronic ester (2.42 mmol), K2CO3 (2 M/H2O, 7.27 mL, 14.5 mmol) and Aliquat® 336 (3 drops) in 25 ml of toluene was degassed with an argon stream for 15 minutes. Finally 140.1 mg Pd(PPh3)4 (0.121 mmol) were added quickly and the reaction mixture was degassed again and sealed. The reaction mixture was heated to 100 °C in a microwave reactor with 300 W and a maximum pressure of 7 bars for 10 h. The polymers were endcapped with bromobenzene and phenylboronic acid pinacol ester by successively adding a degassed solution (0.5 ml 0.01 M/toluene) via a syringe and 20 minutes of reaction time at 100 °C. Then the organic phase was poured into a mixture of methanol (150 ml) and conc. HCl (20 ml) and stirred overnight. The precipitate was separated in a centrifuge and repetitively precipitated from tetrahydrofuran (5 ml) into methanol (100 ml). Finally the polymer was filtered off, dried in S4 vacuum and subjected to sequential Soxhlet extraction with acetone for 2 days to remove low molecular weight species.