Prominent Signatures of Energy Transfer in Action-Detected Spectra of a Cyanobacterial Photosynthetic Protein

TL;DR

This study demonstrates that action-detected 2DES can effectively reveal energy transfer dynamics in cyanobacterial proteins, challenging previous assumptions about its limitations in large aggregates.

Contribution

It shows that the 1/N sensitivity limit does not apply to cyanobacterial proteins due to slow annihilation, enhancing the applicability of action detection techniques.

Findings

F-2DES reveals prominent energy transfer signals in cyanobacterial proteins.

The 1/N limit is modified by slow annihilation, contrary to previous assumptions.

Action detection is suitable for probing exciton diffusion in weakly coupled systems.

Abstract

Action-detected two-dimensional electronic spectroscopy (A-2DES) could potentially be a versatile chemical tool with applicability across a range of photophysical observables such as photocurrent, photoionization, or fluorescence. However, a prominent absence of excited state energy/charge transfer dynamics signals in archetypal photosynthetic proteins has suggested severe limitations of A-2DES in probing large aggregates where sensitivity to excited state dynamics is proposed to go down as 1/N, where N is the aggregate size. We report measurements of energy transfer dynamics in a cyanobacterial protein through both conventional and fluorescence 2DES (F-2DES), where the dynamics reported by F-2DES is quite prominent and comparable to that measured by conventional 2DES. Analysis of our experiments combined with coarse-grained simulations of the spectra suggest that the 1/N limit argument, which assumes infinitely fast intra-exciton manifold equilibration, is modified in case of cyanobacterial proteins because of slow annihilation. Our results suggest that action detection may in fact be well-suited to probe exciton diffusion across weakly coupled systems.