The interchain origin of the green emission band in oxidised poly(9, 9-dioctylfluorene) (PFO)

摘要

We report systematic measurements of the evolution of the emission characteristics of PFO whilst undergoing photo-oxidation. Pure PFO and highly diluted PFO/polystyrene blended films were prepared for the studies by spin-coating. Each film was oxidised by exposure to the 351 nm line of a cw Ar~+ laser. Both the kinetics of the various spectral components and the photoluminescence intensity for each film was monitored as a function of oxidation time and their respective behaviours were compared. Our results demonstrate that there is a strong tendency for singlet intrachain excitons initially created on pristine PFO segments to migrate to the fluorenone moieties produced by photo-oxidation. However, we conclusively show that emission from states localised at these defect sites cannot account for the appearance of the broad green emission band (g-band) that is well-known to occur in degraded polyfiuorenes. Instead, it is shown that the g-band must emanate from interchain states that are formed after energy has been transferred to the fluorenone moieties (either via energy transfer from non-defective PFO segments or by direct excitation).