Localized exciton states in pi-conjugated polymers with finite torsion

TL;DR

This paper studies how finite torsion in pi-conjugated polymers causes localized exciton states, analyzing their energies and optical properties, and relating findings to recent experimental optical studies.

Contribution

It introduces a theoretical model linking torsion-induced transfer integral perturbations to localized exciton states and their optical characteristics in conjugated polymers.

Findings

Localized states occur when cosine of torsion angle exceeds unperturbed value

Energy of localized states depends on ratio of perturbed to unperturbed transfer integrals

Optically active states' oscillator strength varies with energy

Abstract

We investigate localized exciton states in pi-conjugated polymers with finite torsion. The localized states are associated with a perturbed transfer integral for which the magnitude of cosine of the torsion angle exceeds the magnitude of the corresponding cosine of the unperturbed system. The localized state energy is calculated as a function of the ratio of the perturbed to unperturbed transfer integrals. Particular attention is paid to the optically active symmetric localized states, and the effective oscillator strength, or square of the absolute magnitude of the transition dipole moment, is calculated as a function of the energy. The relation of the theory to recent optical studies of poly(di-noctylfluorene)(PF8) is discussed.