Controlling the Morphology of Conjugated Polyfluorene through Physical Stretching and Solvent Variation

In this paper, the intentional control of morphology and photophysical properties of a conjugated polydiarylfluorene, PODPF, in thin films is achieved through various systematic approaches including physical stretching when hosted in a highly elastic polymer, poly(vinyl butyral) (PVB) at various weight-to-weight ratios, and by varying the solvent. Microspectroscopic techniques were employed to monitor the resulting variations. Significant differences in the excitation and emission spectra are observed as functions of the concentration of PODPF mixed in the PVB film. This indicates the formation of different types of aggregates in these films through the coupling between dipoles with different relative orientations. Fluorescence anisotropy images show dramatic differences as a function of the extent of physical stretching of the film and as a function of PODPF concentration. Shifts in the emission spectra of the films as a function of the concentration in films cast from different solvents illustrate that the morphology of the films is highly dependent on the properties of the solvent from which the film is cast. The results highlight effective approaches for influencing the morphology and properties of conjugated polymers in thin films, with particular emphasis on the crucial role of solvent selection. Theoretical modeling is also employed to provide insight into the underlying principles governing these observed phenomena.