  Ring torsion effects on optical excitation properties in poly(para-phenylene)
(PPP) and polyaniline (PAN) are investigated by extending the Shimoi-Abe model
[Synth. Met. 78, 219 (1996)]. The model is solved by the intermediate exciton
formalism. Long-range excitons are characterized, and the long-range component
of the oscillator strengths is calculated. We find that ring torsions affect
the long-range excitons in PAN more easily than in PPP, due to the larger
torsion angle of PAN and the large number of bonds whose hopping integrals are
modulated by torsions. Next, ring torsional disorder effects simulated by the
Gaussian distribution function are analyzed. The long-range component of the
total oscillator strengths after sample average is nearly independent of the
disorder strength in the PPP case, while that of the PAN decreases easily as
the disorder becomes stronger.
