Morphology and optical properties of poly(9,9' dioctyfluorene) films

This thesis concerns a study of the optical properties of the polymer poly(9,9'dioctylfluorene) (PFO). Polyfluorene polymers represent the current state-of-the-art materials for use in optoelectronic devices. Recently there has been a growing interest in investigating how changes in polymer morphology affect their optical properties and in turn how such information can be used to optimise device performance. The first part of this thesis deals with the characterization of PFO films prepared in four morphological phases, namely: as spin coated glass (SC PFO), nematic quenched glass (NQ PFO), crystalline (X PFO) and PFO having an extended chain conformation (beta-phase PFO). Infrared (FT-IR) and Raman spectroscopy have been used in order to correlate the polymer chain conformations in the four phases with the results reported from optical measurements. In order to do this, it has been necessary to analyse and assign the origin of the vibrational modes detected. This has been achieved via comparison with molecules chemically similar to PFO. Theoretical modelling has been used to confirm our assignment. The changes detected in the Raman and Infrared spectra indicate that the polymer chains adopt a longer conjugation length in the X and beta-phase films. It appears that the side chains in the X PFO and beta-phase conformation have a lower concentration of defects (alternation of gauche and trans conformation) than is observed in the SC film. Low temperature Raman and photoluminescence (PL) measurements are used to identify the vibrational modes that are more strongly coupled with the S sub 0 sub - >S sub 1 electronic transition. The second part of this thesis leads with the study of the influence of temperature on the exciton migration process in the SC and beta-phase films. At low temperature the migration process is slower and it is detectable via picosecond time resolved luminescence measurements. I have investigated the effect of temperature on the absorption, P