Excitons and nonlinear optical spectra in conjugated polymers

Abstract

Excitons in conjugated polymers are studied theoretically in the Su-Schrieffer-Heeger model supplemented by long-range Coulomb interactions. The relationship between exciton energies and basic interaction parameters is clarified. Linear and third-order nonlinear optical susceptibilities (two-photon absorption, electroabsorption, and third-harmonic generation) have been calculated, elucidating the significance of singlet and triplet excitons and unbound electron-hole pairs. Using only moderate interaction strength, various experiments in polydiacetylene can be interpreted in a consistent way.