Effects of structural disorder on two-particle exciton–phonon excitations in organic materials

Abstract

In this paper we explore the effects of diagonal structural disorder on the optical absorption line shapes for two-particle exciton–vibron bound states and for exciton–vibron continua. ’’Local-type’’ two-particle bound states are drastically broadened by disorder scattering, while ’’band-type’’ two-particle continua are only slightly affected by disorder scattering. These results are utilized as a diagnostic tool to distinguish between local-type and band-type many-particle excitations, establishing that the two-particle singlet exciton–vibron excitation in crystalline and in amorphous films of tetracene and pentacene corresponds to a two-particle continuum.