Mapping the Fluorescence Decay Lifetime of a Conjugated Polymer in a Phase-Separated Blend Using a Scanning Near-Field Optical Microscope

摘要

We have studied a blend of the polymers poly(9,9-dioctylfluorene)(F8)dispersed in an inert matrix of polystyrene (PS) using time-resolved scanning near-field optical microscopy(SNOM).On spin-casting,phase separation occurs between the two polymers resulting in a thin film characterized by an F8-rich phase and a PS-rich phase.By spatially mapping the intensity of photoluminescence from the film,we find that there is a low concentration of F8 trapped within the PS-rich phase.We find that the fluorescence emission lifetime(measured at 440 nm)of F8 trapped within the PS-rich phase is significantly longer than that from the F8-rich phase(290 ps compared to 235 ps).Furthermore,spectral measurements indicate that the F8 emission from the PS-rich phase is characterized by a reduced fraction of emission from fluorenone defect states.Taken together,our measurements suggest that in the PS-rich phase interchain exciton diffusion between F8 molecules is suppressed significantly by the effect of dilution.