jp7b02812_si_001.pdf (1.1 MB)
Photochemistry and Electron Transfer Kinetics in a Photocatalyst Model Assessed by Marcus Theory and Quantum Dynamics
journal contribution
posted on 2017-07-07, 00:00 authored by Alexander Koch, Daniel Kinzel, Fabian Dröge, Stefanie Gräfe, Stephan KupferThe
present computational study aims at unraveling the competitive
photoinduced electron transfer (ET) kinetics in a supramolecular photocatalyst
model. Detailed understanding of the fundamental processes is essential
for the design of novel photocatalysts in the scope of solar energy
conversion that allows unidirectional ET from a light-harvesting photosensitizer
to the catalytically active site. Thus, the photophysics and the photochemistry
of the bimetallic complex RuCo, [(bpy)2RuII(tpphz)CoIII(bpy)2]5+, where
excitation of the ruthenium(II) moiety leads to an ET to the cobalt(III),
were investigated by quantum chemical and quantum dynamical methods.
Time-dependent density functional theory (TDDFT) allowed us to determine
the bright singlet excitations as well as to identify the triplet
states involved in the photoexcited relaxation cascades associated
with charge-separation (CS) and charge-recombination (CR) processes.
Diabatic potential energy surfaces were constructed for selected pairs
of donor–acceptor states leading to CS and CR along linear
interpolated Cartesian coordinates to study the intramolecular ET
via Marcus theory, a semiempirical expression neglecting an explicit
description of the potential couplings and quantum dynamics (QD).
Both Marcus theory and QD predict very similar rate constants of 1.55
× 1012 – 2.24 × 1013 s–1 and 1.21 × 1013–7.59 ×
1013 s–1 for CS processes, respectively.
ET rates obtained by the semiempirical expression are underestimated
by several orders of magnitude; thus, an explicit consideration of
electronic coupling is essential to describe intramolecular ET processes
in RuCo.