Structural study of helical polyfluorene under high quasihydrostatic pressure

Area of Science:

• Materials Science
• Polymer Chemistry
• Condensed Matter Physics

Background:

• Poly(9,9-bis(2-ethylhexyl)fluorene) (PF2/6) is a conjugated polymer with a helical backbone structure.
• Understanding how external stimuli affect polymer conformation is crucial for materials design.

Purpose of the Study:

• To investigate the effect of high quasihydrostatic pressure on the helical structure and unit cell of PF2/6 using X-ray diffraction (XRD).
• To correlate structural changes with pressure-induced modifications in the polymer's backbone conformation.

Main Methods:

• High-pressure X-ray diffraction (XRD) measurements were performed on PF2/6 using a diamond anvil cell up to 10 GPa.
• A theoretical model was developed to calculate X-ray reflection positions based on backbone torsion angles.
• Previously published high-pressure photoluminescence data were reanalyzed.

Main Results:

• XRD data revealed a decrease in the torsion angle between repeat units and partial backbone planarization of PF2/6 between 2 and 6 GPa.
• The hexagonal unit cell order was found to be impaired at pressures at or below 2 GPa, indicated by peak shifts and broadening.
• Reanalyzed photoluminescence data showed qualitative consistency with the XRD findings.

Conclusions:

• High quasihydrostatic pressure can effectively control the helical π-conjugated backbone structure of PF2/6 without chemical modification.
• This study highlights the utility of high-pressure X-ray scattering techniques for probing and controlling the structure of conjugated polymers.
• The findings pave the way for broader applications of high-pressure X-ray scattering in polymer research.