Photoinduced Energy and Electron-Transfer Reactions by Polypyridine Ruthenium(II) Complexes Containing a Derivatized Perylene Diimide

The [Ru(II) (phen) 2 (pPDIp)] 2+ complex, where pPDIp is the symmetric bridging ligand phenanthroline–perylene–phenanthroline, shows strong electronic absorption bands attributed to the pPDIp and {Ru(phen) 2 } 2+ moieties in acetonitrile. The charge-separated intermediate {Ru(III) (phen) 2 (pPDIp –• )} 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 3 *pPDIp-Ru(II) (τ P = 1.8 μs) that sensitizes the formation of singlet molecular oxygen with quantum yield ϕ Δ = 0.57. The dyad in deaerated acetonitrile solutions is reduced by triethylamine (NEt 3 ) to the [Ru(II) (phen) 2 (pPDIp •– )] 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) 2 (pPDIp 2– )] 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.