The effects of photochemical oxidation and chain conformation on green emission of poly(9,9-dioctylfluorene)

Abstract

The effects of chain conformation on the photo-oxidation and green emission of poly(9,9-dioctylfluorenyl-2,7-diyl) (PFO) has been investigated at both single-molecule and ensemble levels. Single-molecule studies reveal the conformation of PFO chains to be more globular when cast from THF than from toluene solutions. Intensity transients of the single molecules show that the elongated molecules cast from toluene have more fluctuations due to limited energy transfer along the polymer chains. The more globular chains show monotonic decays with isotropic polarization. Emission spectra of the single molecules show that photochemical oxidation leads to a reduction in the emission of the molecule with no change in the emission spectra. No green emission is ever detected for single molecules, indicating that formation of emissive ketone defects is a rare event. Ensemble studies of chains show that molecules cast from THF develop some green emission upon photodegradation, while those cast from toluene do not. The increase in green emission in the globular molecules suggests that interchain contacts improve energy transfer for emissive ketone defects in the PFO cast from THF.