Dissertation

|3.1 Brominated Phenanthrolines - A Gate to new Bridging Ligands|
of concurring quenching processes (see figure 54 for an example).
5000
4000
Counts
3000
2000
1000
0
0 1 2 3 4 5
t / µs
Figure 54: Representative emission decays from the time correlated single photon counting
experiment (TCSPC). Depicted are the values for Ru(phenBr 2 ) 2 in dichloromethane (–), acetonitrile
(–) and inert acetonitrile (–) with 467 nm excitation. The decays are well fitted to a monoexponential
decay.
The emission decay behavior in aerated solvents of the complexes is slightly changed
by the increasing number of bromo substituents in the 5,6-positions. The complexes
[Ru(tbbpy) 2 (phenBr m )] 2+ (m = 1, 2) show about the same deactivation behavior with shorter
(m = 1, 2)
lifetimes in acetonitrile (τ
ACN
≈ 140 ns) and longer lifetimes in dichloromethane (τ
(m = 1, 2)
DCM
≈ 450 ns). These compounds have a 40 ns longer lifetime, when compared to the reference
compound Ru(phenBr 4 ) (τ
to Ru(phen) (τ
(m = 0)
ACN
(m = 4)
ACN
= 100 ns) and a by 50 ns shortened lifetime when compared
= 211 ns). From this result it was concluded that substitution of the
phenanthroline backbone with halogen substituents (-I/+M effect) has an effect on the excited
3
MLCT state lifetime of the resulting ruthenium complex. According to the emission data in
the series [Ru(tbbpy) 3-n (phenBr 2 ) n
] 2+ (n = 1, 2, 3), it can be figured that substitution of the 5,6-
positions has less influence on the excited state energy than substitution in the 3,8-position. The
ordering of the lifetimes within this series of ruthenium complexes is the same as the ordering of
the relative steady state emission intensities in dichloromethane (τ
(n = 3)
DCM
(n = 1)
= 353 ns < τ
DCM
= 438 ns
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