Another broad
absorption peak is observed at 800 nm that is ascribed to an
exciton located in the quinoid ring.
This peak is evolved due
to the charge transfer from adjacent benzenoid rings with each
side contributing half electron on average (Yang et al., 2007).
The height of this absorption peak provides information of the
extent of doping level. The peak height is detected to increase
until D4, beyond that it is noticed to be same. That is why the
order of conductivity also remains unchanged beyond D4
(shown in Table 2). In other words, the dopant DBSA concentration
remains same although aniline concentration is
increased. Therefore, the dopant concentration in D4 is sufficient
for the available aniline. With increasing aniline concentration,
both the peaks are found to have shifted from a higher
wavelength to a lower wavelength. The increase in aniline
quantity may have increased the compact coil conformation
of the polymer leading to this blue shift.