Structural evolution processes of solution-cast and melt-quenched poly(9,9-di-n-hexyl- 2,7-fluorene) (PFH) were quantitatively examined using small/wide-angle X-ray scattering (SA)(S/WAXS) and differential scanning calorimetry. SAXS/WAXS profiles of solution-cast PFH indicated presence of nanograins (radius of gyration R-g approximate to 5 nm) of 2D-ordered beta phase. Upon heating above T-g, perfected packing order and growth of beta nanograins up to R-g approximate to 10 nm result in suppressed formation of alpha crystallites up to 190 degrees C, beyond which extensive melting accompanied by significant (albeit partial) transformation of beta nanograins into alpha nanocrystals of R-g approximate to 13 nm can be observed in a narrow temperature range of 190 -200 degrees C. Thus transformed alpha crystallites remained stable in size before melting above 235 degrees C. The nanograin structures observed are correlated to phase-dependent optical absorption and photoexcited emission. Results suggest sensitive influences of the size/spatial distribution of beta nanograins (particularly in the layering direction of the 2D-ordered chain packing) on photoexcited emission of the polyfluorene film. (C) 2012 Elsevier Ltd. All rights reserved.