† Department of Chemistry, Clemson University, Clemson, South Carolina 29634, United States
‡ Department of Chemistry, Emory University, Atlanta, Georgia 30322, United States
§ Department of Molecular and Cellular Medicine, Texas A&M University, College Station, Texas 77845, United States
摘要：Many key processes in conjugated polymers are strongly influenced by multiple energy transfer (i.e., exciton diffusion). We investigated the effect of solvent-induced swelling on the kinetics of multiple energy transfer in nanoparticles of the conjugated polymers PFBT and MEH-PPV. Multiple energy transfer between equivalent chromophores results in an increased rate of quenching by defects due to a cascading or funneling effect. The effects of swelling on energy transfer between polymer chromophores and the resulting exciton dynamics were modeled using a random walk on a lattice of chromophores. The simulation results show good agreement with experimental fluorescence quantum yield, and decay kinetics results at low to moderate THF concentrations. We found that the time scale for energy transfer between chromophores (∼5 ps for MEH-PPV nanoparticles and ∼100 ps for PFBT nanoparticles) is highly sensitive to swelling, slowing by an order of magnitude or more for swelled particles. The results support quenching by defects or polarons, amplified by multiple energy transfer or a cascade effect, as a likely explanation for the typically low fluorescence quantum yield of conjugated polymer particles as compared to the free polymer in solution as well as similar effects observed in thin films.