Synthesis, optical properties, and spectral stability of chiral dendronized binaphthyl-containing polyfluorene derivatives

A new kind of chiral dendronized binaphthyl-containing random polyfluorene derivatives bearing different contents (3.2-14.9 mol %) of Frechet's polyether dendritic wedges have been designed and synthesized through a versatile Pd-catalyzed Suzuki polycondensation. Their properties have been investigated by NMR, TGA, DSC, CD, UV-vis, and photoluminescence and compared to those of poly(9,9-dihexylfluorene) (PF). It was found that attachment of Frechet's dendritic wedges into the main chain enhanced the emission efficiency and thermal stability of the copolymers. Furthermore, different from PF, good to excellent spectral stabilities in the solid state were proven for all the dendronized chiral copolymers after a thermal annealing under air at 200 degrees C. The second-generation dendronized polymer P3 bearing about 15 mol % of dendritic pendants exhibited high quantum yields in both solutions and films, and excellent thermal oxidative stability. These results demonstrated that the combination of the twisted nonplanar binaphthyl and the sterically demanding dendron could efficiently suppress the intermolecular packing and aggregation at much lower dendron contents compared to other reported dendronized polyfluorenes. Additionally, the investigation of circular dichroism spectra of these chiral dendronized polymers showed a strong Cotton effect at long wavelength (378-384 nm), indicating that the chirality of binaphthyl unit was transferred to the whole polyfluorene backbone. (C) 2007 Wiley Periodicals, Inc.