Several new ruthenium(II) complexes containing 8-(dimethylphosphino)quinoline (Me
2Pqn) were synthesized, andtheir structures and electrochemical/spectroscopic properties have been investigated. In addition to the mono(Me
2Pqn) complex [Ru(bpy or phen)
2(Me
2Pqn)](PF
6)
2 (
1 or
1'; bpy = 2,2'-bipyridine; phen = 1,10-phenanthroline),the geometrical isomers
trans(P)- and
C1-[Ru(bpy)(Me
2Pqn)
2](PF
6)
2 (
tP-2 and
C1-2) and
mer- and
fac-[Ru(Me
2Pqn)
3](PF
6)
2 (
m-3 and
f-3) were also selectively synthesized and isolated. It was found that complexes
tP-2 and
m-3 were converted quantitatively to the corresponding
C1-2 and
f-3 isomers, respectively, by irradiationof light corresponding to the MLCT transition energy. The strong
trans influence of the Me
2P- donor group ofMe
2Pqn was confirmed by the X-ray structural analyses for
1,
tP-2,
m-3, and
f-3. Cyclic voltammetry of a seriesof complexes, [Ru(bpy)
3](PF
6)
2,
1,
C1-2, and
f-3, exhibited a reversible one-electron oxidation wave and two orthree one-electron reduction waves. The oxidation potentials of the complexes gave a large positive shift withincreasing number of coordinated Me
2Pqn molecules, indicating a larger
![](/images/gifchars/pi.gif)
-acceptability of the Me
2P- group comparedwith bpy or qn. Complex
f-3 in EtOH/MeOH (4:1) glass at 77 K exhibited an intense long-lived (
![](/images/gifchars/tau.gif)
= 920
![](/images/entities/mgr.gif)
s)emission arising from the quinoline-based
3(
![](/images/gifchars/pi.gif)
-
![](/images/gifchars/pi.gif)
*) excited state. In contrast, the mixed-ligand complexes
1,
1',and
C1-2 showed a characteristic dual emission, giving a double-exponential emission decay, and the dual emissionoriginates from both the bpy-based
3MLCT and the quinoline-based
3(
![](/images/gifchars/pi.gif)
-
![](/images/gifchars/pi.gif)
*) emitting states.