The title compound, [Zn(C6H5S)(2)(C18H12N2)], was prepared as a model for future complexes that will be incorporated into light-harvesting arrays. The Zn-II atom lies on a twofold rotation axis and the ligands are arranged tetrahedrally around this atom. The benzenethiolate ligand and the biquinoline ligand are nearly perpendicular to one another, making a dihedral angle of 84.09 (5)degrees. The biquinoline ligand is nearly planar, with a maximum deviation of 0.055 (3) angstrom from the mean plane of the ring system. In the crystal, the molecules pack in a manner such that the biquinoline ligands are parallel to one another, with a pi-pi interaction [interplanar distance = 3.38 (1) angstrom] with the neighboring biquinoline ligand.

In the chromophore-quencher complex fac-[Re(Aqphen)(CO)(3)(py-PTZ)](+) (Aqphen 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 framework. This introduces a third, low-lying, ligand-based pi acceptor level localized largely on the quinone fragment. Laser flash excitation of fac-[Re(Aqphen)(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(298K) = 300 ns (k = 3.3 x 10(6) s(-)(1)). Application of transient absorption, time-resolved resonance Raman, and time-resolved infrared spectroscopies proves 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.

A synthetic procedure has been devised for the preparation of the reductive quencher ligand 4-methyl-4'-(N-methyl-p-tolylaminomethyl)-2,2'-bipyridine (dmb-tol), which contains toluidine covalently bound to 2,2'-bipyridine. When bound to Re(I) in [Re(I)(dmb-tol)(CO)(3)Cl], laser flash Re(I) --> dmb metal-to-ligand charge-transfer (MLCT) excitation at 355 nm in CH(3)CN at 298 +/- 2 K is followed by efficient, rapid (<5 ns) appearance of a transient with an absorption feature at 470 nm. The transient spectrum is consistent with formation of the redox-separated state, [Re(I)(dmb(-)-tol(+))(CO)(3)Cl], which returns to the ground state by back electron transfer with k(ET) = (1.05 +/- 0.01) x 10(7) s(-)(1) (tau = 95 +/- 1 ns) at 298 +/- 2 K. Rapid, efficient quenching is also observed in the Ru(II) complex [Ru(4,4'-(C(O)NEt(2))(2)bpy)(2)(dmb-tol)](2+). Based on transient absorption measurements, a rapid equilibrium appears to exist between the initial metal-to-ligand charge-transfer excited state and the redox-separated state, which lies at higher energy. Decay to the ground state is dominated by back electron transfer within the redox-separated state which occurs with k > 4 x 10(8) s(-)(1) at 298 +/- 2 K.