Restraining the aggregation of poly(9,9-dihexylfluorene) by crosslinked poly(methyl methacrylate) networks

A crosslinked network was used to restrain undesired interchain aggregation of fluorescent polymers in this study. Primarily, solutions of poly(9,9-dihexylfluorene) (PF) in toluene and in curable liquid monomer mixtures of methyl methacrylate (MMA) and ditrimethylolproane tetracrylate (DTTPT) were compared to study the effect of concentration on absorption and emission behaviors. Results from ultraviolet-visible absorption, photoluminescence (PL) emission, and PL excitation reveal that the degree of aggregation depended strongly on the concentration and was correlated to the size of the polymer coil as determined from fight scattering. Solutions of known PF content in MMA/ DTTPT were then photoirradiated to yield PF/crosslinked poly,(methyl methacrylate) (X-PMMA) composite films. Comparison among the pure PF, PF/MMA/DTTPT mother liquid, and PF/X-PMMA solid composites were then conducted to evaluate the effect of crosslinking on the degree of aggregation. With small amounts of imbedded PF (0.0015 wt %), the PF/X-PMMA composite had a PL quantum yield (0.70) higher than the pure PF (0.65) itself. Most notably, the PF/X-PMMA composites after annealing at 120 and 200 degrees C for 5 h still retained a reasonable emission efficiency (with related PL quantum yields of 0.61 and 0.43), in contrast to the large PL quantum yield reductions to 0.32 and 0.19 for the annealed PFs after the same treatment. Suggestively, interchain aggregation during a high-temperature annealing process can be largely inhibited by the surrounding crosslinked network matrix. (c) 2007 Wiley Periodicals, Inc.