Polyfluorene-block-poly(phenyl isocyanide) Copolymers: One-Pot Synthesis, Helical Assembly, and Circularly Polarized Luminescence

Abstract

Optically active π-conjugated block copolymers are of considerable significance and interest, but their controlled synthesis and helical self-assembly remain challenging. In this study, π-conjugated block copolymers consisting of polyfluorene (PF) and poly(phenyl isocyanide) (PPI) segments were facilely prepared in one pot through two sequential polymerizations. First, a Pd(II)-terminated PF precursor was synthesized via the Suzuki cross-coupling polymerization of 7-bromo-9,9-dihexylfluorene-2-boronic acid pinacol ester, which was catalyzed using a Pd(0)/t-Bu3P system. Then, PF-b-PPI copolymers with controlled molar mass and narrow dispersities were fabricated via controlled polymerization of phenyl isocyanide monomers utilizing Pd(II)-terminated PF as the catalyst. Benefiting from the π-conjugated structure of the PF block and the helicity of the PPI block, the resulting PF-b-PPI copolymers could self-assemble into single-handed helical nanofibers. In the self-assembly process, chirality was transferred from the helical PPI block to the self-assembled helical nanofibers, thereby endowing them with optical activity and excellent circularly polarized luminescence properties.