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The study investigates energy transfer dynamics in a cyanobacterial protein using both conventional and fluorescence 2D electronic spectroscopy (F-2DES). Contrary to expectations based on the 1/N scaling argument, F-2DES reveals prominent energy transfer dynamics comparable to conventional 2DES. The authors attribute this to slow annihilation within the protein, which modifies the 1/N limit, suggesting that action detection methods are suitable for probing exciton diffusion in weakly coupled systems.
Action-detected spectroscopy, previously thought limited in large photosynthetic proteins, can effectively probe exciton diffusion in weakly coupled systems due to slower annihilation rates than previously assumed.
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.
