SNAr as a facile method to prepare polystyrene-grafted conjugated copolymers with enhanced photoluminescence properties

The preparation of graft copolymers remains a challenge, especially for conjugated materials, due to the limited number of reactions available for backbone modification. Herein, we report a reliable method to conjugated graft copolymers (also known as rod-graft-coil copolymers) starting from different well studied polymers in a one-step post-polymerisation reaction. The starting polymers all contain a commonly used benzo[c][1,2,5]thiadiazole unit, which includes a fluorine atom as a functional handle for replacement via a nucleophilic aromatic substitution (SNAr) reaction. We functionalised the polymers in a post-polymerisation approach with secondary thiol-terminated polystyrene (PS), readily available from the RAFT polymerisation. Furthermore, we prepared stable, spherical, emissive nanoparticles from the resulting graft copolymers as shown by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The optical properties of the parent and the graft copolymers were studied in solution and solid state, as well as in nanoparticles (NPs). PLQY studies revealed, that the emission was enhanced upon grafting of PS in the NPs. This approach offers the preparation of graft copolymers in one additional step after polymerisation only, and moreover enhances the emissive properties of the resulting graft copolymers in the solid state which is promising in the field of biologically benign fluorescent nanoprobes.