Raman Spectra of Poly(p-phenylenevinylene)s with Fluorinated Vinylene Units: Evidence of Inter-ring Distortion

The Raman spectrum of poly{2-methoxy-5-[(2-ethylhexyl)oxy]- 1,4-phenylenedifluorovinylene} (MEH-PPDFV) is reported and compared with that of a well-known non-fluorinated reference polymer, namely poly{2-methoxy-5-[(2-ethylhexyl)oxy]-1,4-phenylenevinylene} (MEH-PPV). The Raman spectra of both polymers are assigned on the basis of density functional theory calculations of the corresponding oligomers. The main differences between vinylene fluorinated and non-fluorinated structures deal with the intensity, frequency shift and broadening of CC vinylene stretching. Additional differences concern the relative intensities of CC phenylene and vinylene stretching as well as the deformation modes in the range 1250-1350 cm1. It is shown that these effects are due to the larger distortion from planarity of the fluorinated polymer, compared with the nonfluorinated counterpart, induced by repulsive interactions between the fluorine atoms on the vinylene units and the oxygen atoms of the alkoxy groups on the aromatic rings.