posted on 2021-02-19, 01:13authored byYusuke Yoneda, S. Jimena Mora, James Shee, Brian L. Wadsworth, Eric A. Arsenault, Diptarka Hait, Gerdenis Kodis, Devens Gust, Gary F. Moore, Ana L. Moore, Martin Head-Gordon, Thomas A. Moore, Graham R. Fleming
Although photoinduced
proton-coupled electron transfer (PCET) plays
an essential role in photosynthesis, a full understanding of the mechanism
is still lacking due to the complex nonequilibrium dynamics arising
from the strongly coupled electronic and nuclear degrees of freedom.
Here we report the photoinduced PCET dynamics of a biomimetic model
system investigated by means of transient IR and two-dimensional electronic–vibrational
(2DEV) spectroscopies, IR spectroelectrochemistry (IRSEC), and calculations
utilizing long-range-corrected hybrid density functionals. This collective
experimental and theoretical effort provides a nuanced picture of
the complicated dynamics and synergistic motions involved in photoinduced
PCET. In particular, the evolution of the 2DEV line shape, which is
highly sensitive to the mixing of vibronic states, is interpreted
by accurate computational modeling of the charge separated state and
is shown to represent a gradual change in electron density distribution
associated with a dihedral twist that occurs on a 120 fs time scale.