The
[Ru(II) (phen)<sub>2</sub>(pPDIp)]<sup>2+</sup> complex, where
pPDIp is the symmetric bridging ligand phenanthroline–perylene–phenanthroline,
shows strong electronic absorption bands attributed to the pPDIp and
{Ru(phen)<sub>2</sub>}<sup>2+</sup> moieties in acetonitrile. The
charge-separated intermediate {Ru(III) (phen)<sub>2</sub>(pPDIp<sup>–•</sup>)} was detected by transient absorption spectroscopy
upon electronic excitation in either the pPDIp or the complex moieties.
The charge-separated intermediate species decays to generate the triplet
state <sup>3</sup>*pPDIp-Ru(II) (τ<sub>P</sub> = 1.8 μs)
that sensitizes the formation of singlet molecular oxygen with quantum
yield ϕ<sub>Δ</sub> = 0.57. The dyad in deaerated acetonitrile
solutions is reduced by triethylamine (NEt<sub>3</sub>) to the [Ru(II)
(phen)<sub>2</sub>(pPDIp<sup>•–</sup>)] radical anion
in the dark. The electron-transfer reaction is accelerated by light
absorption. By photolysis of the radical anion, a second electron
transfer reaction occurs to generate the [Ru(II) (phen)<sub>2</sub>(pPDIp<sup>2–</sup>)] dianion. The changes of the color of
solution indicate the redox states of complexes and offer a sensitive
reporter of each stage of redox reaction from start to finish. The
reduced complexes can be converted to the initial complex, using methyl
viologen or molecular oxygen as an electron acceptor. The accumulation
of electrons in two well-separated steps opens promising opportunities
such as in catalysis
