Investigation of the Energy Transfer Mechanism Between Semiconducting Polymer Dots and Organic Dyes

Semiconducting polymer nanoparticles (Pdots) are a promising fluorescent probe for a wide variety of bioanalytical applications, including as donors in energy transfer (ET)-based sensing and photodynamic therapy. Although numerous Pdot-ET systems have been developed, detailed characterization of the ET mechanisms in these systems has been comparatively limited. Here, we studied the mechanism of ET between Pdot donors based on poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) and a variety of cyanine and rhodamine dye acceptors using both steady-state and time-resolved spectroscopies. The dyes were either hydrophobic and nonspecifically associated with the Pdot core, or hydrophilic and specifically conjugated to the Pdot surface. Our data suggest that Forster resonance energy transfer (FRET) was the most probable and dominant mechanism of ET. There were no clear indications of photoinduced electron transfer (PET) and no need to distinguish Dexter ET from FRET, but there was an apparent decrease in the quantum yield of the acceptor dyes upon association with the Pdots. We also address how the physical characteristics of the Pdot system complicated and limited detailed photophysical study and models, and, in general, render simple FRET models both quantitatively and qualitatively inadequate. The results of our study contribute to a more complete understanding of the ET processes occurring in Pdot-acceptor systems, support the development of both new and improved applications based on Pdots and ET, and inform directions for further fundamental study.