Photochemistry and Photophysics of Coordination Compounds

Photochemistry and Photophysics of Coordination Compounds: Rhodium 237
tween the three metal centers have been produced as well [111]. The ideal aim
of the molecular design was to achieve complete photoinduced charge separation,
with the positive hole on the iron donor and the electron on monoquat
acceptor. Apparently, however, the redox properties of the molecular components
were not quite ideal. Thus, the Ru(II)-based MLCT excited state is
efficiently quenched. In the transient product obtained, however, the oxidized
site is indeed the iron center but the reduced site seems to be a polypyridine
ligand (in 23, either the bridging dipyridylpyrazine or the terpyridine ligand).
In 23, this charge transfer state reverts to the ground state in 37 ns [111].
The simple chromophore-quencher system 24 also contains a quaternarized
electron acceptor attached to a Rh(III) polypyridine unit. This dyad
was designed [112] to study intramolecular charge shift processes, using
a photochemical inter/intramolecular reaction scheme of the type shown in
Eqs. 15–19.
The dyad, schematized as Rh(III)-DQ, undergoes Rh(III)-localized photoexcitation
(Eq. 15). The excited state is then involved in reductive quenching
(Eq. 16) by a suitable electron donor, 1,3,5-trimethoxybenzene, indicated
as TMB. The reduced dyad originates from the quenching process with the extra
electron on the metal complex moiety, i.e., on the thermodynamically less