Decoherence of Excitons in Multichromophore Systems: Thermal Line Broadening and Destruction of Superradiant Emission

TL;DR

This paper investigates how temperature affects exciton coherence and line broadening in multichromophore systems, revealing a power-law dependence and linking it to coherence length and fluorescence lifetime changes.

Contribution

It provides a quantitative model connecting exciton dephasing, static disorder, and phonon interactions, explaining experimental observations in dye aggregates.

Findings

Absorption line width follows a power-law temperature dependence.

Line width relates to exciton coherence length constrained by phonons.

Fluorescence lifetime increase above 40 K is due to coherence length dropping below localization length.

Abstract

We study the temperature-dependent dephasing rate of excitons in chains of chromophores, accounting for scattering on static disorder as well as acoustic phonons in the host matrix. From this we find a powerlaw temperature dependence of the absorption line width, in excellent quantitative agreement with experiments on dye aggregates. We also propose a relation between the line width and the exciton coherence length imposed by the phonons. The results indicate that the much debated steep rise of the fluorescence lifetime of pseudo-isocyanine aggregates above 40 K results from the fact that this coherence length drops below the localization length imposed by static disorder.