Aggregation-Induced Förster Resonance Energy Transfer in Polybenzofulvene/Dye Nanoparticles

Polymeric nanoparticles are versatile scaffolds to develop smart multichromophoric systems whose collective optical properties can be tuned in view of a specific application. Addition of water (nonsolvent) to diluted THF solutions of a blue emitting π-stacked polymer and a yellow emitting dye induces nanoparticle polymer/dye coaggregation. At 70% water content, concomitantly to nanoparticle shrinking, the emission efficiency increases and the color switches from blue to yellow. Time-resolved fluorescence analysis demonstrates that the switch in the nanoparticle emission is governed by an aggregation-induced Förster resonance energy transfer (FRET) process from the polymer to the molecularly embedded dye activated at a local concentration of about 10^-2 M within the nanoparticles.