Raman spectroscopy of fluorene oligomers in the α-, β- and γ-phases

We present Raman spectroscopy measurements on a series of fluorene oligomers, and compare them with those of the polymer poly(9,9-dioctylfluorene) PF8. We show that such measurements can be used as evidence for the formation of the so-called β-phase in an oligofluorene, and confirm the picture in which the β-phase is stabilized by the adoption of an anti-gauche–gauche side chain conformation. We also demonstrate that Raman spectroscopy can be used to identify the formation of the so-called γ-phase (crystalline phase) in oligofluorene thin films. Our measurements suggest that the rich phase morphology observed in PF8 can often be replicated in thin films of its model oligomers.