Long-range excitons in conjugated polymers with ring torsions: poly(para-phenylene) and polyaniline

TL;DR

This study investigates how ring torsions influence optical excitations in poly(para-phenylene) and polyaniline, revealing that torsions significantly affect long-range excitons and oscillator strengths, especially in PAN, with disorder effects varying between the two polymers.

Contribution

The paper extends the Shimoi-Abe model to analyze ring torsion effects on long-range excitons in PPP and PAN, highlighting differences in disorder sensitivity.

Findings

Ring torsions impact long-range excitons more in PAN than in PPP.

Disorder reduces oscillator strength in PAN but not significantly in PPP.

Long-range exciton characteristics are modulated by torsion angles and disorder.

Abstract

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.