  Experimental/theoretical evidence for sustained vibration-assisted electronic
(vibronic) coherence in the Photosystem II Reaction Center (PSII RC) indicates
that photosynthetic solar-energy conversion might be optimized through the
interplay of electronic and vibrational quantum dynamics. This evidence has
been obtained by investigating the primary charge separation process in the
PSII RC by two-dimensional electronic spectroscopy (2DES) and Redfield modeling
of the experimental data. However, while conventional Fourier transform
analysis of the 2DES data allows oscillatory signatures of vibronic coherence
to be identified in the frequency domain in the form of static 2D frequency
maps, the real-time evolution of the coherences is lost. Here we apply for the
first time wavelet analysis to the PSII RC 2DES data to obtain time-resolved 2D
frequency maps. These maps allow us to demonstrate that i) coherence between
the excitons initiating the two different charge separation pathways is active
for more than 500 fs, and ii) coherence between exciton and charge-transfer
states, the reactant and product of the charge separation reaction,
respectively, is active for at least 1 ps. These findings imply that the PSII
RC employs coherence i) to sample competing electron transfer pathways, and ii)
to perform directed, ultrafast and efficient electron transfer.
