Dissertation

|3.1 Brominated Phenanthrolines - A Gate to new Bridging Ligands|
E 1/2 (̂LL 3 ) ≈ -2.3 V which were assigned to the three ligand centered reductions.
A correlation of the ground state redox properties of a compound A and the emission properties
(one electron potential corresponding to the zero-zero excited state energy) allows a first
approximation of the redox potentials of excited state couples according to the following
equations: [130]
E(A + /A*) ≈ E(A + /A) – E 0-0
E(A*/A − ) ≈ E(A/A − ) + E 0-0
This correlation for the series of ruthenium complexes [Ru(tbbpy) 3-n (phenBr 2 ) n
] 2+ (n = 0, 1, 2, 3)
is depicted in figure 56.
E Red
(MLCT )
LL
-1.20
-1.10
0.70
0.80
tbbpy
* *
d(t ) 2g
E0-0
2.01 eV
(612 nm)
*
E (MLCT) = 0.16 eV
tbbpy
phenBr 2 phenBr2 phenBr 2
* *
E0-0
1.79 eV E0-0
(631 nm)
2.00 eV
(621 nm)
E0-0
2.06 eV
(600 nm)
Ru 3+ Ru 3+ Ru 3+ Ru 3+
0.90
E Ox (Ru 2+/3+ )
d(t )
2g
d(t 2g)
n = 0 n = 1 n = 2
d(t 2g)
n = 3
Figure 56: Combination of the redox potentials of the 3 MLCT excited states that can be tapped
via oxidative quenching mechanism (E(A + /A*)), the ground state redox potential for the oxidation
of the complexes (E(A + /A)) and the emission energies (E 0-0 ) of the series of ruthenium complexes
[Ru(tbbpy) 3-n (phenBr 2 ) n ] 2+ (n = 0, 1, 2, 3).
It can be seen that the excited state oxidation potential remains unchanged at a value of about
1.1 V in the case of n = 1, 2, 3 although the ground state ruthenium centered oxidation potential
is shifted toward higher potentials with increasing number of phenBr 2 -ligands. Furthermore, the
reduction potential of the excited state in the complex with n = 0 (phenBr 2 -free complex) is about
-0.16 V higher. This leads to the conclusion that the energy of the phenBr 2 -centered 3 MLCT-state
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