Transient absorption decay rate constants (k(obs)) for reactions of electronically excited zinc tetraphenylporphyrin ((ZnTPP)-Zn-3*) with triruthenium oxocentered acetate-bridged clusters [Ru-3(mu(3)-O)(mu-CH3CO2)(6)(CO)(L)](2)(mu-pz), where pz = pyrazine and L = 4-cyanopyridine (cpy) (1), pyridine (py) (2), or 4-dimethylaminopyridine (dmap) (3), were obtained from nanosecond flash-quench spectroscopic data (quenching constants, k(q), for (ZnTPP)-Zn-3*/1-3 are 3.0 x 10(9), 1.5 x 10(9), and 1.1 x 10(9) M-1 respectively). Values of k(q) for reactions of (ZnTPP)-Zn-3* with 1-3 and Ru-3(mu(3)-O)(mu-CH3CO2)(6)(CO)(L)(2) [L = cpy (4), py (5), dmap (6)] monomeric analogues suggest that photoinduced electron transfer is the main pathway of excited-state decay; this mechanistic proposal is consistent with results from a photolysis control experiment, where growth of characteristic near-IR absorption bands attributable to reduced (mixed-valence) Ru3O-cluster products were observed.