Chain morphologies in semicrystalline polyfluorene: evidence from Raman scattering

Area of Science:

• Polymer Science
• Materials Science
• Spectroscopy

Background:

• Polyfluorenes (PFs) are conjugated polymers with tunable optoelectronic properties.
• The conformational order of PFs significantly impacts their solid-state morphology and performance.
• Di-octyl substituted polyfluorene (PF8) is a model system for studying structure-property relationships.

Purpose of the Study:

• To investigate the conformational order of the beta phase in PF8.
• To correlate conformational isomers with side and main chain morphology.
• To determine the compatibility of the beta phase with the alpha crystalline phase.

Main Methods:

• Raman scattering spectroscopy was employed to study PF8 under thermal cycling.
• Density-functional theory (DFT) calculations were performed on single-chain oligomers.
• Vibrational spectra from DFT were compared with experimental Raman data.

Main Results:

• The beta phase of PF8 exhibits significant conformational order at the nanoscale.
• Thermal cycling reveals a direct link between conformational isomers and chain morphology.
• DFT calculations confirm the incompatibility of the beta phase with the alpha crystalline phase.

Conclusions:

• The beta phase represents a distinct, ordered conformational state in PF8.
• The coexistence of alpha and beta phases is unlikely due to structural incompatibility.
• Understanding these phases is crucial for controlling PF8 morphology and applications.