Full Length ArticleMolecular relaxation temperature of poly (9.9-dioctylfluorenyl-2.7-diyl) using the Franck-Condon emission analysis

•PL spectrum analysis of polyfluorene thin film considering two emitting species.•Evaluation of electron-vibrational coupling modes by Franck-Condon scope.•Acquisition of β-relaxation and its activation energy by Franck-Condon analysis.

We report on the Franck-Condon analysis of temperature dependence emission spectra (140- 340 K) of spin-casted poly(9.9-dioctylfluorenyl-2.7-diyl)(PF8) thin films. The photoluminescence spectra were analyzed considering the contribution of two species: isolates and aggregates. Results obtained from photoluminescence excitation and confocal spectroscopy measurements corroborate the hypothesis of two emitting species. FT-IR and Raman spectroscopy were used to obtain the effective electron-vibrational modes for the isolate (700 cm−1) and aggregate (1250 cm−1 and 1400 cm−1) species, providing values to be used in the Franck-Condon analysis. From the half maximum Gaussian bandwidth (Δε), we calculated an activation energy of approximately 250 meV for the inter-chain interaction (aggregates species), which were associated with the onset of movement on the polymer׳s side chain (β-relaxation).