Inelastic X-Ray Scattering Study of Exciton Properties in an Organic Molecular crystal

TL;DR

This study uses inelastic x-ray scattering to investigate exciton properties in an organic molecular crystal, revealing exciton dispersion and confirming the localization of the Frenkel exciton within the molecule, demonstrating IXS as a powerful investigative tool.

Contribution

First application of IXS to study excitons in a complex organic molecular crystal, providing detailed dispersion data and validating quantum chemical calculations.

Findings

Exciton dispersion of 130 meV observed.

Quantum calculations match the measured dielectric response.

Frenkel exciton confined within a fraction of the molecule.

Abstract

Excitons in a complex organic molecular crystal were studied by inelastic x-ray scattering (IXS) for the first time. The dynamic dielectric response function is measured over a large momentum transfer region, from which an exciton dispersion of 130 meV is observed. Semiempirical quantum chemical calculations reproduce well the momentum dependence of the measured dynamic dielectric responses, and thus unambiguously indicate that the lowest Frenkel exciton is confined within a fraction of the complex molecule. Our results demonstrate that IXS is a powerful tool for studying excitons in complex organic molecular systems. Besides the energy position, the IXS spectra provide a stringent test on the validity of the theoretically calculated exciton wave functions.