Near-term aging and thermal behavior of polyfluorene in various aggregation states

Steady-stage photoluminescence and photoabsorption have been used to characterize the impact of aggregation in various poly(di-n-alkylfluorene) thin films. Highly aggregated films exhibit systematic changes in the photoluminescence while aging. These are indicative of a gradual increase in interchain interactions. Nonaggregated films do not exhibit this behavior. However the mesomorphic properties are altered and these films undergo irreversible changes on thermal cycling. All these properties appear to be correlated with changes in the local short-range molecular packing.