Qg. Mulazzani et al., QUENCHING OF THE EXCITED-STATES OF RUTHENIUM(II)-DIIMINE COMPLEXES BYOXYGEN, Journal of physical chemistry, 98(4), 1994, pp. 1145-1150
The quenching by O-2 of the MLCT excited states of 10 Ru(II)-diimine c
omplexes (RuL(2+)) of the form Ru(bpy)(3-m-z)(bpm)(m)(bpz)(z)(2+) (bpy
= 2,2'-bipyridine, bpm = 2,2'-bipyrimidine, bpz = 2,2'-bipyrazine, m
and z = 0, 1, 2, 3 and m + z less than or equal to 3) in aqueous solut
ion has been investigated using the techniques of laser flash photolys
is and time-resolved and steady-state near-infrared emission spectroph
otometry. Values of k(q), have been determined in H2O and D2O and rang
e between 5.1 x 10(8) and 3.4 X 10(9) M(-1) s(-1). The quantum yields
(Phi(Delta)) of singlet molecular oxygen, O-2((1) Delta(g)), originati
ng from the energy-transfer quenching of RuL(2+) by O-2 and determine
d in D2O by comparison with Phi(Delta) from the excited state of tetra
kis(4-sulfonatophenyl)porphine (TPPS4-), are 0.5 for Ru(bpy)(3)(2+) an
d similar to 1 for all the other complexes. It has been established th
at for Ru(bpy)(3)(2+) and, presumably, all the other complexes the yie
ld of electron-transfer products, RuL(3+) and O-2(.-), in bulk solutio
n, is negligibly small. The lower value of Phi(Delta) for Ru(bpy)(3)(2
+) is attributed to competitive charge-transfer quenching, followed by
efficient back electron transfer within the solvent cage. The values
of the rate constants of energy transfer for the six complexes that co
ntain at least one bpz ligand decrease with increasing driving force.