Excited-state electron transfer in a chromophore-quencher complex. Spectroscopic identification of a redox-separated state

In the chromophore-quencher complex fac-[Re(Aqphen)(CO)(3)(py-PTZ)](+) (Aqp hen is 12,17-dihydronaphtho-[2,3-h]dipyrido[3,2-a:2',3'-c]-phenazine-12,17- dione; py-PTZ is 10-(4-picolyl)phenothiazine), Aqphen is a dppz derivative, containing a pendant quinone acceptor at the terminus of a rigid ligand fr amework. This introduces a third, law-lying, ligand-based pi* acceptor leve l localized largely on the quinone fragment. Laser flash excitation of fac- [Re(Asphen)(CO)(3)(py-PTZ)](+) (354.7 nm; in 1,2-dichloroethane) results in the appearance of a relatively long-lived transient that decays with tau(2 98K) = 300 ns (k = 3.3 x 10(6) s(-1)). Application of transient absorption, time-resolved resonance Raman, and time-resolved infrared spectroscopies p roves that this transient is the redox separated state fac-[Re-I(Aqphen(.-) )(CO)(3)(py-PTZ(.+))](+) in which the excited electron is localized largely on the quinone portion of the Aqphen ligand.