Modern Polymer Spect..

30 20 10 0
ENERGY / lo3 cm-l
Figure 4-6. Absorption spectra
of !a) undoped and (b) electrochemically
Bu4N +(n-type)-
doped poly~,y-phenylene) films.
Arrows indicate the positions of
excitation wavelengths (488.0.
514.5, 632.8, 720. and 1064 nm)
used for Ranian measurements
[66J.
40
.
0
30
>
u
(r
w
z
;
0
20
u
0
10
2 3 4 5
NUMBER OF RINGS
Figure 4-7. Observed electronic transition energies
of p-oligophenyls. (a) Neutral species: (b) band I of
the radical anions; (c) band 11 of the radical anions;
(d) band I' of the dianions. The data of neutral
p-oligophenyls are taken from 1671. The data of the
radical anions and dianions are taken from [69, 701.
sition energy of poly(p-phenylene), 27400 cn-', is lower than that of PP6, 31 500
cni-' , indicating that the conjugation length of poly( p-phenylene) is much longer
than 6. Upon Bu4N+ doping) two broad absorptions appear at about 5600 cm-'
(1 800 nm) and 19 400 cm-' (5 15 nm). The assignments of these bands will be discussed
in the next section on the basis of the spectra of the radical anions (PPn-)