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

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.