Signatures of Exciton Delocalization and Exciton-Exciton Annihilation in Fluorescence-Detected Two-Dimensional Coherent Spectroscopy

TL;DR

This paper compares fluorescence-detected 2D spectroscopy with standard 2D spectroscopy in studying exciton delocalization and annihilation in molecular heterodimers, highlighting how fluorescence detection isolates specific excitonic processes.

Contribution

It introduces a theoretical framework for understanding differences between F-2DES and standard 2DES, and proposes using time-gated fluorescence to isolate exciton annihilation effects.

Findings

F-2DES and 2DES measure exciton delocalization differently.

Cross-peaks in spectra are influenced by exciton annihilation and relaxation.

Time-gated fluorescence can isolate annihilation contributions.

Abstract

We present calculations of the fluorescence-detected coherent two-dimensional (F-2DES) spectra of a molecular heterodimer. We compare how the F-2DES technique differs from the standard coherently detected two-dimensional (2DES) spectroscopy in measuring exciton delocalization. We analyze which processes contribute to cross-peaks in the zero-waiting-time spectra obtained by the two methods. Based strictly on time-dependent perturbation theory, we study how in both methods varying degree of cancellation between perturbative contributions gives rise to cross-peaks, and identify exciton annihilation and exciton relaxation contributions to the cross-peak in the zero-waiting-time F-2DES. We propose that time-gated fluorescence detection can be used to isolate the annihilation contribution to F-2DES both to retrieve information equivalent to 2DES spectroscopy and to study annihilation contribution itself.