Tuning the emission and lighting the circularly polarized luminescence of polyfluorene by incorporating a non-emissive polycarbene

Abstract

Facile fabrication and control over the self-assembly of π-conjugated block copolymers are greatly desired in the field of organic semiconducting materials. In this work, polyfluorenes carrying a Ni(II)-terminal were first prepared via Ni(II)-catalyzed quasi-living Kumada catalyst-transfer polymerization, the chain of which is extended with chiral diazoacetates carrying an S- or R-methylbenzyl ester, giving poly(fluorene)-b-polycarbene copolymers in high yield with controlled molar mass and low dispersity. Although the monomers have different structures and polymerization mechanisms, the one-pot block copolymerization proceeded in a living manner. The diazoacetate chirality induced an asymmetric polymerization, rendering the polycarbene block to adopt a one-handed preferred helix. Interestingly, polyfluorene showed blue emission with circularly polarized luminescence (CPL) silent, whereas the resulting block copolymers showed cyan emission with clear CPL. Further studies revealed that the block copolymers self-assembled into one-handed helical nanofibers with defined handedness. Through asymmetric self-assembly, the chirality was transferred to the supramolecular assemblies, endowing the achiral polyfluorene with high optical activity and CPL.