Laser Control of Dissipative Two-Exciton Dynamics in Molecular Aggregates

TL;DR

This paper demonstrates how ultrafast shaped laser pulses can control two-exciton dynamics in molecular aggregates, potentially suppressing decay channels and enhancing high excitation densities using a theoretical approach.

Contribution

It introduces a method to manipulate two-exciton states in molecular aggregates via pulse optimization within a dissipative Frenkel exciton model.

Findings

Ultrafast shaped laser pulses can influence two-exciton dynamics.

Decay of two-exciton populations can be transiently suppressed.

Dissipative hierarchy equations effectively model exciton-vibrational interactions.

Abstract

There are two types of two-photon transitions in molecular aggregates, that is, non-local excitations of two monomers and local double excitations to some higher excited intra-monomer electronic state. As a consequence of the inter-monomer Coulomb interaction these different excitation states are coupled to each other. Higher excited intra-monomer states are rather short-lived due to efficient internal conversion of electronic into vibrational energy. Combining both processes leads to the annihilation of an electronic excitation state, which is a major loss channel for establishing high excitation densities in molecular aggregates. Applying theoretical pulse optimization techniques to a Frenkel exciton model it is shown that the dynamics of two-exciton states in linear aggregates (dimer to tetramer) can be influenced by ultrafast shaped laser pulses. In particular, it is studied to what extent the decay of the two-exciton population by inter-band transitions can be transiently suppressed. Intra-band dynamics is described by a dissipative hierarchy equation approach, which takes into account strong exciton-vibrational coupling in the non-Markovian regime.