Vibronic origin of long-lived coherence in an artificial molecular light harvester

TL;DR

This paper investigates the origin of long-lived coherence in an artificial molecular light harvester, demonstrating that vibronic coupling between excitons and vibrations sustains coherence, supported by experimental and theoretical analysis.

Contribution

It provides the first combined experimental and theoretical verification that vibronic coupling causes long-lasting coherence in an artificial light harvesting system.

Findings

Vibronic coupling sustains long-lived coherence.

Polarization-controlled 2D spectroscopy reveals specific optical responses.

Analytical expressions identify conditions for prolonged coherence.

Abstract

Natural and artificial light harvesting processes have recently gained new interest. Signatures of long lasting coherence in spectroscopic signals of biological systems have been repeatedly observed, albeit their origin is a matter of ongoing debate, as it is unclear how the loss of coherence due to interaction with the noisy environments in such systems is averted. Here we report experimental and theoretical verification of coherent exciton-vibrational (vibronic) coupling as the origin of long-lasting coherence in an artificial light harvester, a molecular J-aggregate. In this macroscopically aligned tubular system, polarization controlled 2D spectroscopy delivers an uncongested and specific optical response as an ideal foundation for an in-depth theoretical description. We derive analytical expressions that show under which general conditions vibronic coupling leads to prolonged excited-state coherence.