Managing intramolecular energy transfer in well-defined polyfluorenes grafting one/two orange emissive groups on central or terminal fluorene unit

Three sets of polyfluorenes grafting one/two orange emissive groups on central or terminal fluorene unit have been synthesized successfully through the catalyst-transfer polymerization. The molecular weights linearly increase with increase in the feed ratios of [monomer]/[catalyst] in a certain molecular weight range. The initiators with bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) (IPr) as the ancillary ligand show better catalytic activity, leading to higher molecular weight of up to 126.3 kDa. All polymers in toluene have the similar absorption spectra to polyfluorene homopolymer, while the weak absorption bands of 420–500 nm are observed only in the polymers with low molecular weight. Photoluminescence spectra display a dominant blue emission from the polyfluorene backbone and a weak orange emission (508–661 nm) from the orange group. The clearly enhanced orange emission in the polymers with low molecular weight is mainly ascribed to the intramolecular Forster energy transfer from the polyfluorene segment to the orange group, which is further confirmed by the electroluminescent behavior of the polymers.