Correction to “Torsional Dynamics and Intramolecular Charge Transfer in the S₂ (1¹B_u⁺) Excited State of Peridinin: A Mechanism for Enhanced Mid-Visible Light Harvesting”

Quantum Coherent Excitation Energy Transfer by Carotenoids in Photosynthetic Light Harvesting

“…Considerable attention has focused on the electronic effects of the carbonyl substitution of the conjugated polyene backbone 14 (Figure 1c) and of the strained conformations assumed in the PCP structure, 15 both of which are thought to enhance peridinin's function as an energy donor by enhancing its excited-state intramolecular chargetransfer (ICT) character. 16,17 We report here results from broad-band two-dimensional electronic spectroscopy (2DES) 20 that show directly that extraordinarily fast excitation energy transfer processes in PCP are initially mediated by quantum coherent mechanisms and mixed peridinin−Chl exciton states at room temperature. 2DES provides a crucial tool for studies of excitation energy transfer processes in light-harvesting proteins and chromophore aggregates because it identifies the pathways of energy transfer between donor and acceptor states.…”

“…Simultaneously, the system−bath reorganization energy, λ, increases owing to the enhanced ICT character that peridinin develops as it twists and bends. 16,27 The transition from the quantum coherent to the localized regime occurs when J ≤ λ. 33 As discussed previously, 17 this condition accompanies formation of an intermediate state of peridinin, S x , 29,34 which we assign to distorted S 2 structures relaxing with respect to out-of-plane coordinates down the steep potential energy gradient toward a conical intersection (or seam) with the S 1 state, where nonradiative decay occurs.…”

“…33 As discussed previously, 17 this condition accompanies formation of an intermediate state of peridinin, S x , 29,34 which we assign to distorted S 2 structures relaxing with respect to out-of-plane coordinates down the steep potential energy gradient toward a conical intersection (or seam) with the S 1 state, where nonradiative decay occurs. 16,27,35 At waiting times T > 50 fs, after the decay of the ESA signal arising from transitions to doubly excited exciton states, the 2DES spectrum from PCP (Figure 5) exhibits a distinct, more slowly decaying ESA signal as an off-diagonal cross peak spanning the 560−640 nm region of the detection axis. This spectrum is comparable to that observed in 2DES spectra from β-carotene 36 or peridinin in solution.…”

Structural Tuning of Quantum Decoherence and Coherent Energy Transfer in Photosynthetic Light Harvesting

“…Incoherent energy transfer from localized peridinins to the Chl a or Chl b acceptors follows the decay of quantum coherence in PCP. A distinct band of ESA, assigned to transitions of the localized S x state to a higher singlet state S n , 29,30 is observed just above the diagonal of the 2DES spectrum at waiting times T > 50 fs. A corresponding feature is observed in the 2DES spectra from the wtPCP−Chl a complex.…”

“…20,24,27,28 The results also indicated, however, that the short-lived S 2 state serves as the donor state for a much faster energy transfer process, possibly involving a quantum coherent mechanism. 20−25 Recent investigations in this laboratory using heterodyne transient grating spectroscopy with 40 fs pulses 16,29,30 focused on determining the nature of this faster process and on characterizing the nonradiative decay processes in peridinin that accompany it. At least 2/3 of the energy transfer yield in PCP was estimated to originate from the S 2 state of peridinin with a 30 fs time constant.…”