Spectroscopic Analysis of a Biomimetic Model of Tyr<sub>Z</sub> Function
in PSII
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Abstract
Using
natural photosynthesis as a model, bio-inspired constructs
for fuel generation from sunlight are being developed. Here we report
the synthesis and time-resolved spectroscopic analysis of a molecular
triad in which a porphyrin electron donor is covalently linked to
both a cyanoporphyrin electron acceptor and a benzimidazole–phenol
model for the Tyr<sub>Z</sub>-D<sub>1</sub>His190 pair of PSII. A
dual-laser setup enabled us to record the ultrafast kinetics and long-living
species in a single experiment. From this data, the photophysical
relaxation pathways were elucidated for the triad and reference compounds.
For the triad, quenching of the cyanoporphyrin singlet excited state
lifetime was interpreted as photoinduced electron transfer from the
porphyrin to the excited cyanoporphyrin. In contrast to a previous
study of a related molecule, we were unable to observe subsequent
formation of a long-lived charge separated state involving the benzimidazole–phenol
moiety. The lack of detection of a long-lived charge separated state
is attributed to a change in energetic landscape for charge separation/recombination
due to small differences in structure and solvation of the new triad