Composite and Blends of PFD and MEH-PPV Conjugated Polymer Nanoparticles: Combined Optical Properties and Quantum Yield Increase by FRET.

Conjugated Polymer Nanoparticles (CPNs) exhibit photophysical properties that depend strongly on morphology, chain conformations, solvent conditions, synthesis processes, the polymer chain's length and distribution, and interchain/intrachain interactions. The production of CPNs using combinations of two different conjugated polymers can be used to create nanocomposites, by mixing previously formed CPNs from distinct polymers, and to create blend CPNs, by mixing distinct polymers prior to the formation of the CPNs. These two methods can produce diverse nanoparticle solutions with distinct properties due to the interaction between the chosen conjugated polymers. In this work, we fabricated water-dispersible luminescent CPNs from the combination of two distinct conjugated polymers: Poly-[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene], MEH-PPV, and poly-(9,9-di-n-dodecylfluorene-2,7-diyl), PFD. The CPNs prepared separately and subsequently mixed exhibit the combined optical properties of the individual CPNs. More importantly, our results show that in CPNs fabricated with both polymers mixed prior to the formation, PFD can transfer energy by Förster resonance energy transfer (FRET) to MEH-PPV. The FRET efficiency is highly dependent on the concentration and ratio of the polymers, reaching values of efficiency above 90% for distances of the order of 4 nm. This energy transfer in blend nanoparticle samples (CPN/PFD:MEH-PPV) resulted in an overall enhancement of the photoluminescence quantum yield of the hybrid nanoparticles, reaching values up to two times higher than those measured for pure CPN/MEH-PPV nanoparticles. These findings show that the donor-acceptor ratio controls energy-transfer efficiency by regulating the fraction of interacting donor-acceptor pairs in hybrid conjugated polymer nanoparticles, enabling applications in luminescent nanostructures, sensing, and photonic devices.