Reduced excimer formation in polyfluorenes by introducing coil-like poly[penta(ethylene glycol) methyl ether methacrylate] block segments

The formation of the aggregate and excimer in light-emitting polyfluorenes during annealing at high temperatures was reduced by adding coil-like block segments through atom transfer radical polymerization (ATRP), initialized by 2- bromoisobutyrate end-capped PF macroinitiator using CuBr/N,N,N',N',N''-pentamethyldiethylenetriamine (PMDETA) catalyst system. The rod-like macroinitiator was synthesized by the Yamamoto-type coupling using a Ni(COD)2 catalyst. The structure and physical properties were characterized by 1H NMR, thermal analysis, GPC, photoluminescence, small angle X-ray scattering and transmission electron microscopy. The addition of the coil-like block segments to the rod-like block segment resulted in the microphase separation between the component blocks which decreased the effective conjugation length of the conjugated moieties. The photoluminescence spectra measured from the thin films of the block copolymers revealed that the coil-like endblocks, attached to the conjugated block segments, suppressed the excimer formation of the PF molecules during annealing at high temperature.