Modern Polymer Spect..

4.7 Poly(y-phenylene) 225
Figure 4-13. Raman spectra of Na-doped poly( -
p-phenylene) taken with various wavelengths of excitation
lasers. (a) 488.0; (b) 514.5; (c) 632.8: (d) 720, (e)
1064 nm [70].
1500 1000
RAMAN SHIFT / Cm-'
Figure 4-14. Resonance Ranian spectra of the radical anions
of p-oligophenyls in THF solutions. (a) p-Terphenyl; (b)
p-quaterphenyl; (c) p-quinquephenyl; (d) p-sexiphenyl. Excitation
wavelengths are 458.0 and 514.5 nm for (a) and (b-d),
respectively. The bands of the solvent are subtracted [70].
t
t
(I)
2
W
b
z
2
<
2
4
LT
1500 1000
RAMAN SHlFT/cm-'
the chain length. The intensities of the bands observed in the 1032-991 and 780-
753 cm-' regions decrease as the chain length becomes longer, indicating that these
bands are associated with the terminal rings. The bands observed in the 780-753
cni-' region show an upshift in wavenumber, as the chain length becomes longer.
This result indicates that the wavenumbers of these bands can be used as a measure
of the localization length of polarons. The bands observed in the 1325-1305 c1n-l
region are assigned to the inter-ring CC stretch [70, 92, 981. The corresponding
bands in neutral PPIZ are observed in the range between 1278 and 1275 cm-'. About
40-cm-' upshifts are explained by the increased TC-bond orders of the inter-ring CC
bonds, i.e., shortening of the inter-ring CC bond lengths. In PP?, the calculated