Blue light emitting cationic polyfluorene polymer(PF)/montmorillonite (MMT) nanocomposites were prepared by solution intercalation and exfoliation method to evaluate the effect of MMT on the nanocomposite structures, properties and morphologies. The properties of PF-MMT composites, containing 1-50 mass% MMT, were characterized unambiguously with the help of multiple analytical techniques, with focus on the keto defect and photostability of PF in the nanocomposites. XRD and HRTEM studies reveal both exfoliation of MMT galleries at lower content of MMT in composites and intercalation of PF chains into the MMT galleries at higher MMT content. The nanocomposites show higher thermal stability than pristine PF as anchorage of nanoclay in PF matrix occur through the electrostatic interaction between nanoclay and polymer. The decrease in Si-O-Si stretching frequency during exfoliation is much higher than in intercalation, as Si-O-Si experience lesser hindrance to vibrate in exfoliated MMT galleries. The gradual redshift of pi-pi* transition peak of PF with increasing MMT content in composites confirms the uncoiling of PF in clay galleries. The photoluminescence characteristics reveal interruption of interchain interaction in this intercalated and exfoliated organic/inorganic hybrid system, which reduces the low-energy emission that results from keto defect. Due to very high aspect ratio of MMT, it can act as an efficient exciton blocking layer and a barrier to oxygen diffusion, which may lead to a device with high color purity and enhanced photostability. Again current-voltage characteristics of nanocomposite films confirm the retention of LED properties after nanocomposite formation. (C) 2011 Elsevier Inc. All rights reserved.