Ka. Opperman et al., INTRAMOLECULAR, PHOTOINDUCED ELECTRON-TRANSFER IN RUTHENIUM(II) BIPYRIDINE-QUINONE COMPLEXES, Inorganic chemistry, 33(23), 1994, pp. 5295-5301
Intramolecular electron transfer quenching following metal-to-ligand c
harge transfer (MLCT) excitation of complexes of Ru-II containing the
ligand yridyl)-4-methyl)-9,10-anthraquinone-2-carboxamide (bpy-AQ) hav
e been investigated by transient emission and absorption measurements.
For [Ru-II(bpy)(2)(bpy-AQ)](2+) (bpy is 2,2'-bipyridine) in acetonitr
ile at room temperature, partial quenching of the initial (Ru-II(bpy)(
2)) excited state occurs as evidenced by decreased emission quantum yi
elds (0.062 vs 0.011) and lifetimes (980 vs 158 ns) relative to [Ru-II
I(bpy(.-))(bpy)(dmb)](2+) (dmb is 4,4'-dimethyl-2,2'-bipyridine). In
[Ru-II(tmb)(2)(bpy-AQ)](2+)(tmb is 4,4',5,5'-tetramethyl-2,2'-bipyridi
ne), electron transfer quenching is nearly complete (Phi(cm) = 0.002,
tau = 6 ns). In neither case is there evidence for AQ(.-) (lambda(max)
= 590 nm) by transient absorption measurements, and it is concluded t
hat the expected redox-separated states, e.g., [Ru-III(bpy)(2)(bpy-AQ.
(-))](2+), undergo rapid back electron transfer to return to the groun
d states. MLCT excitation of the donor-chromophore-acceptor complex [R
u-II(bpy-AQ)(2)(bpy-PTZ)](2+) [bpy-PTZ is {10- [(4'-methyl-2,2'-bipyri
din-4-yl)methyl] phenothiazine}] leads to formation of the redox-separ
ated state [Ru-II(bpy-AQ)(bpy-AQ(.-))(bpy-PTZ(.+))](2+) (lambda(max)(-
PTZ(.+)) = 510 nm) in approximately 40% yield. It undergoes back-elect
ron-transfer to give the ground state with k (25 degrees C, CH3CN) = 6
.7 x 10(6) s(-1).